Institut für Meteorologie und Klimatologie

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ATTENTION:
This page is no longer maintained and will be removed until December, 31st, 2010.

Our new documentation can be found under  palm.muk.uni-hannover.de

PALM group (Head: Siegfried Raasch)

 

Our main research tool is the parallelized Large-Eddy Simulation (LES) Model PALM, the original version of which was developed from 1997-1999 at our institute. This model is optimized for use on massively parallel computers, and it is therefore very well suited for simulations with an extremely large number of grid points. The current supercomputer of the North German Supercomputing Center "Norddeutscher Verbund für Hoch- und Höchstleistungsrechnen" (HLRN), an SGI-ICE machine with 12000 cores, allows calculations with up to 40963 grid points. Further information on PALM is available using the PALM quick links below. Our research focusses on the analysis of micro- and mesoscale turbulent boundary layers. Other key parts of our work include numerical improvements of PALM, in particular parallelized numerical schemes, and the development of software systems that are able to effectively visualize the extremely large data amount that is typical of parallelized models.   The photo shows our research group (as of August 2009) in front of some of the nodes of the new HLRN-II SGI Altix computer. From left to right: Naoki Ikegaya, Gahyun Goh, Carolin Weinreis, Jungwha Lee, Jens Kampmeyer, Theres Franke (Front)  Siegfried Raasch (Head), Rieke Heinze, Björn Witha, Björn Maronga, Marcus Letzel, Micha Gryschka, Yvonne Breitenbach (Back) (Photo: G. Gaus)

 

Contents of this page: Contact details  (address, members) Current research projects  (short description) Future research topics  (short description) Previous research projects  (short summary) Links  (conferences, co-operations) Publications (under participation) of the PALM group: Reviewed publications since 1997 Recent work submitted for publication Selected conference abstracts

PALM quick links: General introduction User manual Technical/numerical documentation  (some parts only in German) Further technical documentation  (internal only) HLRN (hice/lcsgih and bice/lcsgib) linux cluster (lcmuk) DKRZ Presentations from the Zingst seminars: 2004 2005 2007 2008 2009 Presentations from the RIAM seminar 2009 Presentations from the UIB/NORCOWE seminar 2010 Animations

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Contact details

Address

Leibniz University of Hannover
Institute of Meteorology and Climatology
PALM group
Herrenhäuser Str. 2
30419 Hannover
Germany

Members

 

Name	e-mail	Ext.*	Room
Franke, Theres		2680	F221
Fricke, Jens		2396	F210
Gryschka, Micha		3254	F236
Heinze, Rieke		4413	F225
Kampmeyer, Jens		3232	F233
Kanani, Farah		3232	F233
Knigge, Christoph		2680	F221
Maronga, Björn		2680	F221
Raasch, Siegfried (Head)		3253	F231
Sühring, Matthias		4413	F225
Voß, Linda		3232	F233
Weinreis, Carolin		4413	F225
Witha, Björn		3232	F233
Fax		4418

*Phone number +49 511 762-Ext.
 

Former members and visitors (function)

 

Breitenbach, Yvonne (Diploma student)
Hamann, Ulrich (Diploma student)
Harbusch, Guido (Diploma student)
Herold, Marcus (Diploma student)
Ikegaya, Naoki (visiting student)
Inagaki, Dr. Atsushi (visiting student)
Jang, Mi-jin (visiting student)
Jansen, Dr. Heiko (researcher)
Kang, In-Soo (visiting student)
Krane, Martina (Diploma student)
Letzel, Dr. Marcus (researcher)
Lin Cai Feng, Sarah (visiting student)
Lotz, Johannes (visiting student)
Noh, Prof. Dr. Yign (visiting researcher)
Rautenhaus, Marc (student)
Rottmann, Tobias (student)
Schröter, Dr. Michael (researcher)
Steinfeld, Dr. Gerald (researcher)
Uhlenbrock, Dr. Jörg (researcher)
Weinbrecht, Dr. Sonja (researcher)
Zhang, Jin (visiting student)

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Current research projects
short description, in chronological order sorted by starting date:

• Coriolis instability in coupled atmosphere-ocean LES
  Responsible: cand.met. Jens Fricke
  Project type: Diploma Thesis (In Cooperation with Igor Esau at Nansen Environmental and Remote Sensing Center, affiliated with the University of Bergen, Norway)
  Duration: 01/04/2010-31/03/2011
  
  The Coriolis force does not change the total energy of a flow. However it does affect its hydrodynamic stability with respect to small perturbation and therefore modifies the energy budget indirectly by transferring energy between the three velocity components. In the past, these instability mechanisms (e.g. inflection point instability) have been studied theoretically and numerically, both, in the atmospheric boundary layer (driven by a body pressure force), and the ocean mixed layer (driven by the surface stress). The studies identified very large effects of the Coriolis force on the flow structure.
  
  In this thesis, the effect of the Coriolis force will be studied for the first time for the coupled atmosphere-ocean boundary layer under neutral / freshwater conditions, using coupled PALM simulations for atmosphere and ocean.

• LES of atmospheric boundary layer turbulence - Contributions to the improvement of turbulence parameterisation schemes by means of systematic studies of higher order statistical moments and their budgets
  Responsible: Dipl.-Met. Rieke Heinze
  Project type: Research project funded by the German Weather Service (DWD-Extramurale Forschung)
  Duration: 1/11/2009-31/10/2012
  
  Even in high resolution weather and climate models the turbulence of the atmospheric boundary layer can not be resolved because the underlying processes are on scales much smaller than the grid resolution used in these models. Accordingly, the whole turbulence spectrum has to be parameterised. A lot of these parameterisations are based on the budgets of the second order statistical moments. The budgets are required for example for the estimation of the relative importance of the respective budget terms as well as for the general applicability of the used parameterisation schemes.
  
  In this project all the budgets of the second order moments shall be determined with aid of LES. The focus is on the study of convective boundary layers with clouds to examine the influence of various cloud regimes on the budgets. Therefore, it is planned to simulate a boundary layer with trade-wind cumulus as well as with stratocumulus and under a situation of a cold air outbreak. Further, the influence of inhomogeneities on the various budget equations will be studied.

• Footprint modelling via LES for the LITFASS-2003 measuring campaign
  Responsible: cand.met. Farah Kanani
  Project type: Diploma Thesis
  Duration: 19/10/2009-18/10/2010
  
  In heterogeneous terrain, the measurement of turbulent fluxes involves several difficulties. The flux that is measured at a certain sensor point is not produced directly beneath the sensor, but is rather produced in areas upwind of the sensor. Therefor, the areas of influence on a flux measurement have to be determined to diagnose the representativeness of a measurement. The area of influence is called “footprint” of a measurement.
  
  In this diploma thesis footprints shall be determined for the measuring sites of the LITFASS-2003 measuring campaign using the parallelized LES-model PALM. These footprint results, computed by a numerical footprint model, shall then further be used to validate the results of an analytical footprint model which was used prior to LITFASS-2003 to estimate which measuring site is most representative for the respective vegetation in the vicinity of the sensor.
  
  

• Development of a higher order advection scheme and its implementation in PALM
  Responsible: cand.met. Matthias Sühring
  Project type: Diploma Thesis
  Duration: 19/10/2009-18/10/2010
  
  The numerical solution of the advection equation holds qualitatively strong dependencies on the wavenumber. Even scales in the range of the grid length show large errors in amplitude and phase speed. Furthermore, lower order discretization of the advection term implicates non-physical oscillations at strong gradients. So Stevens at al. (1999) assume that the resolved entrainment flux at the top of the boundary layer depend on the quality of the advection scheme. The 5th order finite difference scheme of Wicker and Skamarock (2002) possesses a well trade-off between numerical properties and computational costs.
  
  This thesis deals with the development of a higher order finite difference scheme based on the scheme of Wicker and Skamarock (2002) and its implementation in PALM. Also an optimization for large numbers of processors shall be accompanied. Furthermore, simulations of the convective boundary layer are planned to show the enhanced numerical properties of this higher order advection scheme.
  
  

• Influence of small scale heterogeneities on the near surface turbulence structure
  Responsible: cand.met. Linda Voß
  Project type: Diploma Thesis
  Duration: 22/09/2009-21/09/2010
  
  Inhomogeneities due to differences in the surface structure may trigger secondary circulations in the convective boundary layer. Turbulence measurements with the eddy-covariance method are not able to detect these fluxes. Heterogeneities with diameters of a few hundred meters are therefore suspected to be partly responsible for the non-closure of the energy balance in a height of 2 m (height of energy balance stations).
  
  Within this thesis high resolution LES simulations for such small scale heterogeneities shall be performed and analyzed with respect to possible stationary near surface circulations.
  
  

• LES study on the effect of secondary circulations on the boundary layer turbulence during LITFASS-2003
  Responsible: cand.met. Björn Maronga
  Project type: Diploma Thesis
  Duration: 18/06/2009-17/06/2010
  
  Former large-eddy simulation (LES) studies of UHLENBROCK (2006) investigated the turbulent structure of the atmospheric boundary layer over heterogeneous land surfaces during the LITFASS-2003 measurement campaign. The results showed the development of thermal induced mesoscale circulations (such as roll convections) and its impact on fluxes of different scales in the
  boundary layer.
  
  Within the scope of this diploma thesis some of these simulations shall be repeated with technical improvements of the parallelized LES-model PALM. Furthermore, correlations between the structure of the secondary circulations and the land surface heteorogeneities shall be identified, especially in case of roll convections, to give better explanations about the structure of these circulations.
  
  In addition to this purpose, corresponding PALM simulations considering topography and possibly a vegetation model could be compared to the “flat” simulations.
  

• Investigations of self organized and forced roll convection during a cold air outbreak with LES
  Responsible: cand.met. Jens Kampmeyer
  Project type: Diploma Thesis
  Duration: 01/04/2009-30/03/2010
  
  This Thesis deals with two types of roll convection.
  At first, the laminar scenario conditions from Gryschka M. et.al (2005) are used to generate self organized roll convection via turbulent inflow according to Lund, T. et al. (1998).
  In the second part, results of Gryschka M. et.al 2008 are used for investigate the influence of ice inhomogeneities to so called forced rolls. Therefore the subjection of explicit ice gabs-variation to roll-reaching in flow direction will be studied.
  
  

• Numerical Simulation of the interaction between the atmosphere and the wing circulation
  Responsible: Dipl.-Met. Carolin Weinreis
  Project type: DFG research project
  Duration: 01/12/2008-30/11/2011
  
  This project generates realistic meteorological scenarios in an existing model for wing circulations in order to study the interaction between the turbulent atmosphere and the wing circulation.
  
  It is of huge relevance to examine the behavior of aircrafts at its known limits especially during approach and therefore to get the feasibility to expand these limits. Experiments are mostly afflicted with excessive risks and costs thus numerical simulations are the alternative and powerful method. The dynamic of the lower turbulent atmosphere needs to be included in these models for a detailed investigation.
  
  The meteorological scenarios are obtained by high-resolution large-eddy simulations. PALM is used to produce these scenarios with the necessary turbulent elements ranging from few meters up to the height of a convective boundary layer.

• Investigations on in-cloud turbulence effects on drop growth and precipitation formation
  Responsible: Dipl.-Met. Theres Franke
  Project type: DFG research project within the priority programme MetStröm
  Duration: 01/02/2008-31/01/2010
  
  The project addresses an intensively discussed problem of cloud microphysics, namely the effect of an in-cloud turbulent flow field on drop growth and precipitation formation. The questions to be answered are: Which influence has the local cloud turbulence on the collision efficiency of small cloud droplets and thus on the coagulation function where the latter is an important ingredient for numerical simulations of precipitation development? What is the impact of turbulence on cloud microphysics compared to the traditional approach disregarding this effect?
  
  Referring to the study PALM is used to perform high-resolution large-eddy simulations of three-dimensional convective clouds in which a large number of water droplets (Lagrangian droplets) is simulated explicitly. The focus is on the spatial and temporal evolution of the droplet spectrum, the spatial distribution of the droplet concentration and the water droplet tracks within turbulent clouds.

• Coupled Atmosphere-Ice-Ocean Turbulence Resolving Model
  Responsible: Dr. Igor Esau, PD Dr. Siegfried Raasch, Dr. Marcus Oliver Letzel
  Project type: Cooperation with Dr. Igor Esau at Nansen Environmental and Remote Sensing Center, affiliated with the University of Bergen, Norway
  Duration: 01/03/2007- (ongoing)
  
  The project objective is to develop a coupled lower atmosphere-ice-upper ocean turbulence resolving model able to simulate interactions between atmospheric and ocean turbulence in presence of sea ice freezing, melting and transporting mechanisms.

• The Physics of turbulence over Antarctic leads and polynyas and its parameterization: a joint study using observations, LES and a micro-/mesoscale model
  Responsible: Dipl.-Met. Björn Witha
  Project type: Joint project with the Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Dr. Christof Lüpkes (funded by DFG)
  Duration: 01/03/2007-31/12/2009
  
  Web page of the joint project: BOLE
  
  In regions with large sea ice concentrations there are always open water areas called leads or polynyas depending on their shape. The length of leads varies between a few kilometres and tens of kilometres and their width ranges from several meters to kilometres. The strong sensible and latent heat fluxes above such areas can trigger convection which significantly modifies the atmospheric boundary layer (ABL). For this reason leads are supposed to have a large influence on the energy exchange between the polar ocean and the atmosphere.
  
  The goals of this project are to get a better understanding of the still not well understood effects of leads and polynyas on the boundary layer turbulence and to clarify their importance for the energy budget and structure of the ABL.
  Results of the LES model PALM and new helicopter based observations of turbulence over leads will be used to (further) develop parameterizations of the lead effect which can be used in models with different grid sizes ranging from microscale non eddy resolving models to weather forecast and regional climate models. The parameterizations are tested in the nonhydrostatic model METRAS.
  

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Short description of future research topics:

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Previous research projects
short summary, in chronological order sorted by starting date

• Scalar transfer process of the urban canopy
  Responsible: Naoki Ikegaya, BSc
  Project type: Coursework for Master in "Architectural Engineering" at Kyushu University (research collaboration between Prof. Aya Hagishima at Kyushu University, Fukuoka, Japan; Urban and Architectural Environment Laboratory, Interdisciplinary Graduate School of Engineering Sciences (IGSES) and Dr. Marcus Oliver Letzel)
  Duration: 01/04/2009-30/09/2009
  

• LES of Kármán vortex streets in the atmospheric boundary layer
  Responsible: cand.met. Rieke Heinze
  Project type: Diploma Thesis
  Duration: 15/10/2008-14/10/2009
  
  Atmospheric vortex streets consist of mesoscale eddies with vertical axis in the wake of large islands. They resemble classical Kármán vortex streets which occur in laboratory experiments behind a cylinder. The islands after which vortex streets appear typically have diameters about 20km and mountain tops about 2-4km. Usually, vortex streets can be found in the stratocumulus capped mixed layer over the ocean when there is a strong elevated inversion well below the island top. Since then, the air is forced to go mainly around the mountain and the stratocumulus clouds act as tracer.
  
  The object of the project is the investigation of atmospheric vortex streets with aid of LES. The topography consists of a single idealized mountain. Characteristic parameters like shedding rate or propagation velocity shall be determined. At first, the dry version of PALM is used to generate Kármán like vortex streets. Then, it is planned to simulate a stratocumulus capped boundary layer with vortex street like cloud pattern.

• LES study on the applicability of the Taylor Hypothesis in the urban boundary layer
  Responsible: cand.met. Yvonne Breitenbach
  Project type: Diploma Thesis
  Duration: 31/03/2008-30/06/2009
  
  Tower measurements only give direct information on the vertical and temporal structure of the urban atmosphere; horizontal information may be deduced using Taylor’s Hypothesis of frozen turbulence (Taylor, 1938). In vegetation canopy flow, however, the local mean velocity is an insufficient estimator for the convection velocity, and near the canopy Taylor’s Hypothesis is not applicable (Shaw et al., 1995). The stiff urban canopy poses the same questions: is Taylor’s Hypothesis valid, and if so, which is the best estimator for the convection velocity in the urban roughness sublayer?
  
  To answer these questions, PALM directly evaluates and compares single-point and two-point statistics.

• Study of the turbulence intensity in a wind turbine wake with the aid of LES
  Responsible: Johannes Lotz
  Project type: Coursework for "Computational Engineering Science", RWTH Aachen University
  Duration: 01/02/2008-31/05/2008
  
  Turbulence may be very large in wind turbine wakes and especially if turbines are clustered in arrays significant interference effects take place. To avoid damage and bad efficiency it is advantageous to get to know the characteristics of this turbulence intensity. In this project the turbine is placed in an environment with turbulence properties similar to the ones of the atmosphere. The wind turbine is modelled by drag forces applied at the grid points corresponding to the projected disk area.

• LES of quarters in Hong Kong
  Responsible: cand.met. Carolin Weinreis
  Project type: Diploma Thesis (research collaboration between Prof. Edward Ng at The Chinese University of Hong Kong, Department of Architechture and Dr. Marcus Oliver Letzel)
  Duration: 01/11/2007-31/10/2008
  
  This project is a cooperation with the Chinese University of Hong Kong. The objective of this study is to investigate the ventilation on pedestrian level in two selected quarters of Hong Kong (Tsim Sha Tsui and Mong Kok in Kowloon).
  
  Hong Kong as one of the most densely built-up and populated cities in the world has a strong interest to improve their urban climate by increasing the natural wind flow within the city. Very tall buildings, certain architectural structures or street positions have the capability to enhance the wind velocity.
  
  PALM is used to simulate the wind flow and to explicitly resolve the turbulent structures around obstacles. For direct comparison simulations with different wind directions and topographies are generated.
  
  Our purpose of this study is to provide guidelines for urban designers. How can they plan future projects in Hong Kong to improve the ventilation?

• Turbulence structure in the urban roughness sublayer:
  LES reference studies and comparison with data from wind tunnel, scale model and field measurements
  Responsible: Dr. Marcus Oliver Letzel
  Project type: DFG research project within the priority programme MetStröm
  Duration: 15/07/2007-14/07/2009
  
  The multi-scale turbulence within and above urban areas poses an open question concerning generation and interaction of coherent structures that is essential for urban turbulence parameterizations in meteorological models: does it resemble vegetation canopy turbulence or surface layer turbulence or does it form an own turbulence type?
  
  This large-eddy simulation (LES) reference study investigates the turbulence structure of the urban roughness sublayer for different canonical cities with consideration of thermal effects. The reasons for the choice of LES for this study are: a) LES is the only numerical method to explicitly resolve the multi-scale turbulence within and above real-size obstacles without significant influence of parameterizations and b) LES offers more applications and is able to deliver more extensive data than the wind tunnel. The project aims at an unprecedented combination of domain size and resolution. Quality assurance includes comparison with data from wind tunnel, scale model and field measurements.

• Large eddy simulation of flow and pollutant dispersion in street canyons
  Responsible: cand.met. Martina Krane
  Project type: Diploma Thesis
  Duration: 11/12/2006 - 10/12/2007 
  
  The objective of the project is the examination of turbulent wind flow and pollutant dispersion in street canyons. A street canyon is a narrow street flanked by tall buildings. The street canyon domain is a region where large amounts of pollutants are released near the ground from motor vehicle exhausts and near the roof level from domestic (or industrial) chimneys. The analysis and forecasting of a single source contribution to the total pollution does require a fairly precise knowledge of the dispersion process inside the street canyon. The flow inside a street canyon is characterized by manifold recirculation regions overlapping with complex wake structures and the fluid motion governing the dispersion process is highly turbulent. To understand the flow and dispersion characteristics inside street canyons a lot of studies have already been made.
  An often used model to analyse flow and pollutant dispersion in street canyons is the k- ε model, which parametrizes the turbulence of the flow completely.
  Sini et al. (1996: Pollutant dispersion and thermal effects in urban street canyons; Atmos. Env. Vol. 30, No. 15, 2659-2677) have shown that for wind directions approximately perpendicular to the street canyon three different flow regimes depending on the value of the aspect ratio (street width/ canyon height) are formed, the isolated roughness flow, the wake interference flow and the skimming flow. The number and arrangement of the vortex inside the street canyon affect the vertical exchange and so the pollutant dispersion inside the street canyon significantly. Aim of this project is to use the LES-model PALM, which resolves the turbulence of the flow, to analyse if Sini et al. describe the vortex inside the street canyon correctly and if the turbulence parametrization in k- ε models can describe the turbulent exchange in street canyons quantitatively and qualitatively correct. Besides this the flow pattern and the pollutant dispersion inside street canyons shall be examined for three different aspect ratios.
  

• Large eddy simulation of the surface boundary layer for wind energy applications
  Supervisors: Dr. T. Neumann (DEWI GmbH) and PD Dr. Siegfried Raasch
  Responsible: Dipl.-Phy. Beatriz Cañadillas
  Project type: ModObs: “Atmospheric modelling for wind energy, climate and environment applications: exploring added value from new observation technique”. (Research Training Networks FP6 (MRTN-CT-2005-019369))
  Duration: 01/10/2006-30/09/2009 
  
  In wind energy, mean flow characteristics are the primary focus in many cases, although turbulence effects are important when considering turbine design specifications as well as turbine operation and maintenance costs. Understanding these effects and their origins are the aim of this project. 
  
  This project is divided into two parts:
  
  

• • • The first part will be to check whether the LES simulations verify fairly against observations, making use of off-shore wind data at FINO1 meteorological mast located in the North See.
      This comparison will help to understand better the observations within the PBL as well as to assess the applicability of LES in wind energy, in those cases where the standard measurements (cup anemometers) of the wind flow are not enough.
      
    • The second part will be to get a better understanding of the inflow wind variation over the turbine rotor.

   

• LES of Dust Devils
  Responsible: cand.met. Theres Franke
  Project type: Diploma Thesis
  Duration: 01/09/2006 - 31/08/2007 
  
  The objective of this project is to analyze dust devils in the atmospheric boundary layer using LES, particularly regarding to its thermodynamical structure, formation mechanism and dependency of dust devil characteristics on atmospheric conditions.
  Dust devils are particle loaded vertical convective vortices in the convective boundary layer. They are characterized by high rotating wind speeds, significant electrostatic fields, and by reduced pressure and enhanced temperature at their centers. Convective vortices can be found on Earth and Mars and are formed as a result of vertical instability in the atmosphere (e.g. due to ground heating by strong insolation), wherever a superadiabatic atmospheric lapse rate, a source of vorticity and a supply of sand, dust or debris are present.
  Although there has been more than one century of investigations about dust devils, the knowledge of dust devils is still limited. Former investigations were focused, beside the structure and characteristics of dust devils, at impacts on convection, arid zone erosion and sediment transport. Furthermore theoretical vortex models were developed and compared with observations and laboratory simulations of dust devils. Since a couple of years there also has been LES studies of dust devils. KANAK et al., 2005 likely produced the first LES of dust devil-scale vortices on Earth that had physical characteristics in reasonable agreement with observations. But they also located some limitations and open questions during their work. Within this project it is now tried to analyze and solve some of these and former questions. For those purposes we planned a simulation which resolves the relevant large-scale turbulent structures of the atmospheric boundary layer and the small-scale dust devil itself simultaneously for the first time.
  

• Urban dispersion modelling using parallel large eddy simulation
  Responsible: Jin Zhang, BEng
  Project type: international research student exchange (funded jointly by our group and by Prof. Manabu Kanda at the Department of International Development Engineering, Tokyo Institute of Technology, Japan)
  Duration: 12/04/2006 - 30/03/2007 
  
  This project is a cooperation with the Kanda Laboratory at the Department of International Development Engineering, Tokyo Institute of Technology, Japan, that focuses on the urban climate and enviroment.
  In an urban area, the flow, turbulence structure, and pollutant-transport characteristics are affected by the urban building geometry. To resolve urban climatic problems, it is important to investigate the mechanisms of their impacts. To conduct LES with urban geometry and climate conditions two key problems need to be resolved: Large calculation domain and building resolution. The urban version of PALM has both of these abilities.
  The objective of this LES study is to investigate the flow, turbulence structure, and pollutant transport in varities of urban geometry by employing PALM and the embeded Lagrangian Dispersion Model.
  The first step is to test the possibilty for using Lagrangian Models in PALM which requests a large amount of system resources as millions of particles are released during the simulations. Then some analyses are going to be conducted to investigate the differences between PALM and former LES street canyon studies which used different numerical methods. The second step is going to be analysis between different urban geometries. Several different urban geometries like square array, staggered array are going to be set in different thermal codintions. Finally these results are going to be compared with those from outdoor model experiments COSMO, which is being conducted by members of Kanda Laboratory in Tokyo.

• Footprint model development and validation for homogeneous and inhomogeneous terrain using high resolution large eddy simulation
  Responsible: Dipl.-Met. Gerald Steinfeld
  Project type: DFG research project
  Duration: 01/10/2005 - 30/09/2008 
  
  This project is a cooperation with the working group of Prof. Dr. Thomas Foken, Department of Micrometeorology, University of Bayreuth, Germany. It brings together expertise on measurements, footprint modelling and LES modelling in the near-surface atmospheric boundary-layer. The objective is to develop footprint algorithms that are applicable in horizontally heterogeneous atmospheric boundary-layer flows within a wide range of thermal stratifications.
  Footprint models determine the spatial context of a measurement by defining a transfer function between sources or sinks of the signal and the sensor position. The resulting source area is an important quality assessment tool, e.g. to assess the influence of disturbing terrain elements on the data. Although micrometeorological research focuses increasingly on complex terrain, footprint models developed to date are restricted to idealised cases of horizontally homogeneous flow conditions, and thus cannot consider the impact of inhomogeneity.
  The project focuses on the development and validation of methods to compute footprints above thermally and aerodynamically inhomogeneous surfaces. In a first step, high-resolution LES, allowing the explicit resolution of the turbulent transport processes, will be carried out by the project members of the PALM group. In a second step, the project members of our cooperation partner will modify both forward and backward Lagrangian stochastic (LS) algorithms to account for horizontally heterogeneous flow conditions. The LES datasets will be used both to derive the flow statistics required to run the LS models and to evaluate their produced source areas. The reliability of the footprint results of both LES model and LS algorithms will finally be validated with data from field experiments.
  
  

• Large eddy simulation of oceanic turbulence and its application to the parameterization of vertical mixing
  Responsible: In-Soo Kang, MSc
  Project type: Joint project with the "Department of Atmospheric Sciences", Yonsei University, Seoul, Prof. Yign Noh (jointly funded  by DFG and KOSEF)
  Duration: 01/05/2005 - 31/03/2007
  
  In this project, we will extend the PALM code to be able to simulate and reproduce the realistic turbulence structure of the ocean mixed layer (OML). Through PALM's results we can understand the processes of ocean mixed layer and ocean deep convection which plays an important role int the ocean circulation and  Carbon cycle process. It is used to verify and improve the parmeterization of the vertial mixing process of OGCM (Ocean Gerneral Circulation Model). This project results will contribute to the developement of the realistic OGCM that make better prediction of the ocean and climate.
  

• LES of a cumulus cloud with explicit Lagrangian droplets
  Responsible: In-Soo Kang, MSc
  Project type: PhD project at the "Department of Atmospheric Sciences", Yonsei University, Seoul, Prof. Yign Noh
  Duration: 01/03/2005 -2007
  
  An LES model of a cumulus cloud is developed in which the motion of a large number of water droplets is explicitly simulated. The model provides various important information of the cloud process such as entrainment and internal mixing, the distribution of droplets within a cloud, and the evolution of particle size spectrum. A substantial part of this Korean PhD project is carried out visiting the PALM group in Hannover.
  

• LES study of the spatial representativeness and imbalances of scalar fluxes determined by the temporal EC method
  Responsible: Dipl.-Met. Gerald Steinfeld
  Project type: Research project (funded by DAAD)
  Duration: 01/05/2004 - 30/09/2005
  
  Several of the former projects of the PALM group have dealt with the so-called energy imbalance problem so far. However, during the last years, several papers, dealing with the analysis of field experiments, have reported on the fact that not only an imbalance of energy fluxes could be observed, but that a similar rate of underestimation of carbon dioxide fluxes could also be stated. A detailed understanding of how mass is partitioned at the earth's surface is of particular importance for the derivation of appropriate parameterisation schemes in global climate models. Global climate models will even gain in importance in the context of the monitoring of the agreements on carbon dioxide emission, that are defined in the Kyoto protocol, as they offer the only possibility to get area-wide data on carbon-dioxide fluxes.
  
  In this study, which is a joint project together with Atsushi Inagaki (MSc) from the working group of Prof. Manabu Kanda, Department of International Development Engineering, Tokyo Institute of Technology, Japan, a systematic investigation of the question, whether the phenomenon of an underestimation of the true representative fluxes in connection with the application of the temporal EC method is restricted to temperature fluxes or whether it has also to be stated for fluxes of a passive scalar, such as carbon dioxide. The simulation of EC measurements of scalar fluxes will be carried out for homogeneously as well as heterogeneously heated/cooled boundary layers and under a variation of the magnitude and direction of the geostrophic wind, of the thermal stratification and of the parameters describing the near-surface heat flux inhomogeneity. Moreover, the impact of an inhomogeneous near-surface scalar flux on a potential underestimation of the representative flux will be examined in detail.
  
  
  

• Monte-Carlo-Simulation of Radiation Transfer Through an Inhomogeneous Cloud Layer
  Responsible: cand.met. Ulrich Hamann
  Project type: Diploma thesis, in co-operation with the radiation and remote sensing group
  Duration: 03/11/2003 - 02/11/2004

  A Monte Carlo simulation for radiation models the path of numerous photon packages through the atmosphere. This approach is necessary, if the atmosphere is not horizontally homogeneous, but contains variable formed clouds. The cloud fields used in this work are provided by the LES model of the PALM group. The simulation will include the transfer of wavelength in the infrared, the visible and the UV spectrum. The goal of the simulation are the heating rate at the surface derived from the irradiance as well as the heating inside the clouds. As this method demands a high computational effort, the program will be parallelized
  
  
  

• Investigation of Physical Mechanisms Leading to Cell Broadening and Organization of Convection in Cold Air Outbreaks utilizing High Resolution LES Model Simulations
  Responsible:  Dr. Heiko Jansen
  Project type: individual DFG research project
  Duration: 01/10/2003 - 31/01/2006

  This project is concerned with the organization of convection structures triggered by so called cold air outbreaks (COA), in which cold air from the continent or sea ice areas drifts above relatively warm water. The large gradient in temperature leads to convection, which at first manifests itself by the creation of horizontal rolls. With increasing distance from the coast, the structure at some point changes to hexagonal cells. The corresponding cloud clusters are readily visible in satellite pictures.

  Although research for some decades in this field, numerous open questions remain. For example, the aspect ratio of the cells, defined as the ratio of their diameter to their height, cannot be simulated in models as it is observed. In reality, this ratio attains values between 10 and 30, while in models or in laboratory experiments, values of 3-4 are seen. Furthermore, it is unclear, why sometimes open cells (with downwind areas in the inner part of the cell) and sometimes closed cells (upwinds in the inner part) are observed. The origin of the cloud streets close to the coast is not known, either.
  
  Such questions are addressed using the high resolution, massively parallel LES model PALM.
  
  

• Development of a Large-Eddy Simulation Model for the Ocean Mixed Layer and Its Application to the Process of Mass Transport in the Ocean
  Responsible: PD Dr. Siegfried Raasch
  Project type: Joint project with the "Department of Atmospheric Sciences", Yonsei University, Seoul, Prof. Yign Noh (jointly funded  by DFG and KOSEF)
  Duration: 01/07/2003 - 30/06/2005

In this project, we will extend the PALM code to be able to simulate and reproduce the realistic turbulence structure of the ocean mixed layer (OML). It will also be expanded to simulate the dispersion of concentration and the motion of suspended particles. The model will be applied to clarify the mass transport process in the OML, such as the transport of dissolved gases and the sedimentation of suspended particles with an aim to understand the biogeochemical processes of the ocean. It will also be used to evaluate and improveone-dimensional ocean mixed layer models, which will be applied to an ocean general circulation model.




• Further LES-Study on the Energy Imbalance Problem with Eddy Covariance Fluxes
  Responsible: Dipl.-Met. Gerald Steinfeld
  Project type: DAAD grant and Academic Frontiers Student Exchange Promotion Program In 2003-2004 (MEXT, Japan)
  Duration: 01/06/2003 - 31/05/2004

  This is a joint project together with Prof. Manabu Kanda at the "Department of International Development Engineering", Tokyo Institute of Technology, Japan. It includes a one-year research stay in Japan.

  This study is based on the former co-operation between Prof. Kanda and Dipl.-Met. Marcus Letzel - "LES Study of the Energy Imbalance Problem with Eddy Covariance Fluxes". In their study they carried out simulations of a convective boundary layer with the following prerequisites:
  - horizontal homogenous surface heat flux (or a mere 1D horizontal variation)
  - vanishing horizontal mean value of the vertical velocity.

  In the scope of this project it should be investigated what the effects are on the observed energy imbalance if at least one of these "ideal case" prerequisites does not apply. For example, the presence of inhomogenities is characteristic of the Earth´s surface.

  Therefore it is planned to carry out simulations with a prescribed one-dimensional sinusoidal surface heat flux (parameter studies with e.g. varying maximum amplitude and wavelength) in order to study the effects of the thermally induced meso-scale circulation on the observed energy imbalance characteristics. These studies imply a slightly different definition of energy imbalance compared with the former studies of Kanda et al.

  Furthermore the influence of a synoptic-scale downward movement - as it is observed in high pressure systems - on the energy imbalance should be investigated by a LES-study. The goal is to examine the results of some theoretical studies.

  Finally, some fundamental comparisons between the heat fluxes calculated by the temporal eddy covariance method and calculated the spatial eddy covariance method will be carried out.
   
   

• LES-Study on the Energy Imbalance Problem for Heterogeneous Surfaces
  Responsible: Atsushi Inagaki, MEng
  Project type: Academic Frontiers Student Exchange Promotion Program In 2003-2004 (MEXT, Japan)
  Duration: 01/05/2003 - 31/03/2004

  This is a joint project with PD Dr. Siegfried Raasch and Prof. Manabu Kanda at the "Department of International Development Engineering", Tokyo Institute of Technology, Japan. It includes an 11-month research stay in Germany.

  This study examines the energy imbalance problem using Large Eddy Simulation model. We represent typical a day-time convective boundary layer with no synoptic-scale vertical motion. By means of this, Kanda et al. (2002) have already revealed the basic characteristics of energy imbalance aroused by a horizontally homogeneous surface. Based on this result, this study investigates the case of heterogeneous surface condition. The heterogenity is given as 1-dimensional sinusoidal surface heating as in Letzel & Raasch (2002). In this study, the influence of the complexity or magnitude of heteroginity heating are important and we examine it in detail. (See also the study by Kanda & Letzel.)
  
  
  

• High Resolution LES of Turbulent Flow in the Vicinity of Buildings including Thermal Effects
  Responsible: Dipl.-Met. Marcus Oliver Letzel, MSc
  Project type: individual DFG research projects & PhD scholarship of the German National Academic Foundation (Studienstiftung des deutschen Volkes)
  Duration: 01/01/2003 - 31/12/2006

  The goal of this project is to look into the detailed structure of building-induced turbulence and how it is affected by thermal stratification.

  The parallel cluster architecture of the new Hochleistungsrechenzentrum Nord (HLRN) now principally allows to simultaneously run two coupled or nested model sets on different computer clusters ('grid computing'). This new feature will be applied to PALM within the scope of this project with the aim to extend the scale range of turbulent flow around buildings that is resolvable by LES models by at least an order of magnitude compared with usual models. This yields new prospects for model validation and the development and testing of turbulence parameterizations, especially under convective conditions (unstable thermal stratification).

  Physical analysis will commence with flow around a single cubic obstacle, followed by street canyon flow, for neutral and convective boundary layers. The results will be used to e.g.
  - validate PALM against laboratory (wind tunnel) experiments,
  - analyze differences between high resolution LES and former LES with lower resolution, and
  - evaluate turbulence parameterizations employed in lower resolution models.

  Modelling aspects of this project involve PALM code implementations such as turbulent inflow and noncyclic boundary conditions, horizontal grid stretching or grid nesting (cf. the Diploma projects of Gryschka and Steinfeld, respectively), a dynamic subgrid scale model, thermal building wall boundary conditions, and suitable visualization methods.
  
  

• Large-Eddy Simulations of Boundary Layer Flows (HOST programme)
  Responsible: PD Dr. Siegfried Raasch
  Project type: Student exchange programme funded by the DAAD within the programme "Hochschulpartnerschaften mit Ostasien" (HOST)
  Partners: Department of Atmospheric Sciences, Yonsei University, Seoul, Korea; Department of International Development Engineering, Tokyo Institute of Technology, Tokyo, Japan
  Duration: 01/01/2003 - 31/12/2005

  The principal aim of this project is to allow students just before or at graduate level (students writing their Diploma thesis, Master and PhD students) to acquire the theoretical and practical basics of the large-eddy simulation technique and to particiate in cutting-edge research with interesting and challenging LES applications. This principal aim implies the following individual aims:
  1.  Provide basic knowledge of theory and practice of LES by means of lectures and practical training.
  2.  Further qualification of Diploma and PhD students through practical LES applications within current research projects of the foreign partners.

Within this programme, three PALM seminars were held at Zingst, Germany from 8-14 July, 2003, from 5-11 July, 2004 and from 4-10 July, 2005.

• LES of Suspended Particle Dispersion in the Ocean Mixed Layer
  Responsible: Dipl.-Met. Marcus Herold
  Project type: Funded by the DAAD within the programme "Hochschulpartnerschaften mit Ostasien" (HOST) and by KOSEF
  Duration: 01/01/2003 - 31/12/2003

  This project examines the influence of particle inertia on mean concentration profiles and settling velocity in the ocean mixed layer (OML). Recently, PALM has been used to examine the effects of wave breaking and langmuir circlulation in the OML (Noh, Min & Raasch, 2003). In the present study, the code is extended to simulate particle motion in a Lagrangian framework. Particles are released close to the surface to investigate their three-dimensional motion and the effects of wave breaking and Langmuir circulation. Therefore, the simulation setup is the same as in Noh, Min & Raasch (2003). A one-way coupling of fluid and particles is implemented, assuming a sufficiantly low volume fraction and size of the particles. In this case, Stokes drag can be assumed and the particle acceleration is determined by the difference of fluid and particles and the particle time scale tau_p only. tau_p and the terminal particle settling velocity w_s are used as independent parameters to characterize groups of particles.

  First analyses show that vertical mixing of particles with slow settling velocities (e.g. w_s / u* = 0.01, 0.1) is dominated by the fluid motion and the significant influence of the Langmuir circulation rather than particle inertia. In this case, the mean profiles of particle concentration differ only slightly from the profiles of passive tracers. The particles become well mixed in the OML instead of sinking through the lower boundary. The results are similar for a whole range of Stokes numbers (St = tau_p / tau_f = 0.01, 0.1, 0.3, 1.0)
  However, particles with w_s / u* = 1.0 are more independent of the fluid motion. Some particles are rapidly mixed downward by the Langmuir circulation, but the greater part reaches the terminal settling velocity w_s. Profiles show a distinct concentration maximum which broadens and descends with time.

  High resolution simulations will clarify particle concentrations in space and time and give insight into the mixing process and mass transport within the OML.
   
   

• Investigation of Coherent Structures in the Surface Layer with the Help of Highly-Resolved LES Data
  Responsible: Dr. Sonja Weinbrecht
  Project type: Research (not funded)
  Duration: 01/01/2003 - 26/10/2003

  Within the scope of the comparison of LES-data with data gained by acoustic tomography (see project "Acoustic Tomography of the ABL for the Validation of an LES Model") a simulation with a very high resolution had been performed. The simulation results showed streaky structures which occured near the surface and were visible in the temperature field, the vertical wind field and the wind component in the mean wind direction. Such structures have already been observed in several simulation results and experiments, but not yet in such a high resolution. So these data will be further analysed with respect to the turbulent structures in the surface layer to get a better understanding of the turbulent flow near the surface.
   
   

• Large-Eddy Simulation of Cold Air Outbreaks with a Stationary Domain
  Responsible: cand.met. Micha Gryschka
  Project type: Diploma thesis
  Duration: 10/06/2002 - 08/09/2003

  With recent simulations (Schröter) the PALM group could show that all LES based computations of roll vortices during cold air outbreaks are due to modell insufficiencies, i.e. unphysical conditions. One possible reason could be that a slanted inversion is needed for the generation of roll vortices and thereby a shear flow at the top of the boundary layer. To examine this, it is necessary to simulate the ABL with a stationary model domain. Therefore noncylic lateral boundaries must be implemented into the PALM code, which is part of the work of this thesis.
   
   

• Coupling of LES Models of Different Spatial Resolution Performing on Massively Parallel Computers
  Responsible: cand.met. Gerald Steinfeld
  Project type: Diploma thesis
  Duration: 17/02/2002 - 16/03/2003

  Large-eddy-simulations (LES) resolve the large, energy containing elements of a turbulent flow explicitly, while those elements that are smaller than a specific scale, which depends on the chosen spatial filter, have to be parameterized. As the maximum eddy size decreases with declining distance to a given physical boundary, even the dominant flow pattern are subgrid scale and therefore not resolved explicitly any more in the vicinity of the boundary.

  The presently known parameterization schemes are not able to describe the turbulence near a physical boundary in a fully satisfactory way. Another possibility to consider the turbulence structure near a physical boundary is to run - in addition to the original LES-model - a nested fine grid model in those areas of the coarse-grid domain which are situated near to the physical boundaries.

  Two different kinds of nested grid models are known in literature. On the one hand there exists the concept of one-way-interaction (OWI). Here, information is only transmitted from the coarse to the fine grid, as the boundary conditions for the fine grid model are derived from the coarse grid model. On the other hand, the additional consideration of fine grid data for the evaluation of the coarse-grid data leads to the concept of two-way-interaction (TWI).

  Within the scope of this diploma thesis the possibility to run OWI- and TWI-nesting was added to the parallelized LES-model PALM. It was found out that in the case of using a OWI the non-physical boundaries of the fine grid become an artificial source of production of TKE. A simulation with the same resolution in the coarse and the nested grid showed that this behaviour appears to be independent of the concrete method applied to derive boundary conditions from coarse grid data for the nested fine grid.

  In a similar simulation using the TWI-scheme a different development between coarse and fine grid fields did not occur, which means that the coarse grid data always contains the necessary information to provide appropriate boundary conditions for the nested grid. Further, "real" nesting simulations, applying the TWI scheme led to an improvement compared with the corresponding OWI-scheme results (e.g. no maximum of the variances of u and v  resp. TKE could be observed at the last grid point below the fine grid boundary), but the obtained results were still not totally convincing so that further investigations on these problems exceeding the scope of this diploma thesis would be necessary before nesting can be used as a standard tool in PALM.
   
   

• Regional Evaporation at Grid/Pixel Scale over Heterogeneous Land Surfaces (EVA-GRIPS) - Numerical Investigation of Turbulent Structures over Heterogeneous Land Surfaces with a Parallelized LES model (EVA-NITS)
  Responsible: Dipl.-Met. Jörg Uhlenbrock
  Project type: BMBF project (the sub-project EVA-NITS belongs to the joint project EVA_GRIPS which is part of the framework programme DEKLIM)
  Duration: 01/01/2002 - 31/12/2004

  Main Homepage of the joint project: EVA-GRIPS

  The main goal of the joint proposal EVA-GRIPS is the determination of area-averaged evaporation on the scale of a gridbox of a regional climate model or of pixels of sattelite images over heterogeneous land surfaces. This goal should be achieved through a combination of measurements, numerical modeling and interpretation of satellite data. The special goal in this subproject is the simulation of the atmospheric boundary layer over the Lindenberg area with a very high resolution. The LES-model shall provide independent sets of tubulence data, which will be compared with the measurements of turbulence gathered by experimental groups and which will complete these measurements. Furthermore, these data sets will be used to validate the turbulence-parameterizations of mesocale models.
   
   

• The Influence of Two-Dimensional Surface Heterogeneities on the Structure and Development of the Atmospheric Boundary Layer
  Responsible: cand.met. Marcus Herold
  Project type: Diploma thesis
  Duration: 01/08/2001 - 23/08/2002

  Heterogeneities of the surface vertical heat flux may induce mesoscale circulations. This has been confirmed by recent observations and numerical studies. In the studies of this diploma thesis a parallelized large-eddy simulation model has been used to examine the influences of two-dimensional continuous and discontinuous inhomogeneities arranged in a chessboard-type pattern. Previous numerical studies revealed strong influences of a number of parameters on the strength and type of the secondary circulations. The most important are perturbation wavelength, perturbation amplitude, shape of the inhomogeneity, wind speed and wind direction. Inhomogeneities with a horizontal extent of the boundary layer height or larger were found to have the largest effects on the mean thermal and dynamical properties of the boundary layer, such as vertical temperature profiles and horizontal diffusion. Thus, the purpose of this study was to examine the effects of heterogeneities at scales of tens of kilometers, the scales of which the strongest effects had been reported.

  The simulation results revealed some significant differences to previous studies on one-dimensional heterogeneities of the same size and two-dimensional perturbations of the size of the boundary layer height (and smaller). For example, the development of secondary circulations was found to be strongly dependent on the shape of the inhomogenity. The temporal oscillations found in studies on one-dimensional inhomogeneities could not be observed in runs with discontinuous perturbations of this study. The two-dimensionality also triggers more complex circulation patterns caused by near-surface convergence lines over the areas of high heat flux values and corresponding divergences at boundary layer height. Due to the nature of the velocity field in the circulation, increased horizontal diffusion and velocity variances can be observed in the lower and upper part of the boundary layer, while their values in the middle remain almost unchanged compared to cases with uniform surface heating. (See also the studies by Schröter and Uhlenbrock.)
   
   

• VERTIcal Transports of Energy and Trace Gases at Anchor Stations and Their Spatial and Temporal Extrapolation under COmplex Natural Conditions (VERTIKO) - STructure of turbulent fluxes under INHOmogeneous Surface Conditions (STINHO) - Simulation of Boundary Layer Turbulence
  Responsible: Dr. Michael Schröter
  Project type: BMBF project (the sub-project STINHO belongs to the joint project VERTIKO which is part of the framework programme AFO2000)
  Duration: 01/06/2001 - 31/03/2004

  Main Homepage of the joint project: VERTIKO
  Webpage of the sub-project of our institute: STINHO

  The sub-project STINHO (STruktur des turbulenten Transports über INHOmogener Unterlage) is part of the cooperative project VERTIKO (VERTIkaltransporte von Energie und Spurenstoffen an Ankerstationen unter KOmplexen natürlichen Bedingungen). STINHO consists of 3 parts. The experimental investigations (part 1, http://www.uni-leipzig.de/~meteo/FORSCHUNG/aku/akuindexe.html) about an inhomogeneous surface with acoustical and optical methods provide near surface averaged values of parameters which are relevant for part 2. Part 2 - which is handles in this working group - deals with the high resolution simulation of the near-surface boundary layer above inhomogeneous terrain by means of the parallelized large-eddy simulation model PALM. In addition to the near-surface experiment and to provide information on the real boundary layer structure to initialize the LES the airborne turbulent measurement system HELIPOD is used (part 3).

  The physical description of the energy budget variations unter turbulent flow conditions above homogeneous surfaces is possible using one-dimensional models and/or micrometeorological measuring techniques, which determine the energy exchange processes considering only the height above the underlying surface. Such a procedure does not consider the horizontal energy fluxes, which must exist between different types of the surface in heterogeneous tarrain. Currently accepted parameterizations for the turbulent transport of energy only consider the vertical direction neglecting horizontal energy fluxes.

  The project achieves a better understanding of the turbulent energy fluxes inside the atmospheric boundary layer, because these fluxes consist of horizontal and vertical components especially visibel in experiments and simulations unter inhomogeneous flow conditions near a heterogeneous surface. Project results will contribute to an improvement of the  parameterizations of energy fluxes over heterogeneous terrain for the use in large scale model.
   
   

• LES Study of the Energy Imbalance Problem with Eddy Covariance Fluxes
  Responsible: Prof. Manabu Kanda; Dipl.-Met. Marcus Oliver Letzel, MSc
  Project type: East-Asia Scholarship Programme of the DaimlerChysler AG and the German National Academic Foundation (Studienstiftung des deutschen Volkes)
  Duration: 01/04/2001 - 31/03/2002

  This is a joint project together with Prof. Manabu Kanda at the "Department of International Development Engineering", Tokyo Institute of Technology, Japan. It includes a one-year research stay in Japan.

  The spatial representativeness of heat fluxes obtained with the eddy covariance method from point measurements and the mechanism of the so-called energy imbalance problem are investigated through numerical experiments using PALM. LES experiments are performed for a convective boundary layer over a flat surface as a best case scenario completely free of sensor errors and the uncertainties associated with field mearurements.

  The results of this study are as follows; (1) Point measurements systematically underestimate the heat flux (negative imbalances), which is attributed to local advection effects. (2) Imbalance bias and variance decrease with increasing wind speed. (3) Longer time averaging gives smaller bias but larger variance of imbalance. (4) Higher elevation gives larger bias and variance of imbalance. (5) Turbulent Organized Structures are shown to account for these statistical features of imbalance. (6)  High-pass filters may reduce the variance of imbalance if properly designed. (7) Surface inhomogeneities can significanlty effect the imbalance. (See also the studies by Schröter, Inagaki and Steinfeld.)
   
   

• Application of Tele-Immersion in Wide Area Networks
  Responsible: PD Dr. Siegfried Raasch
  Project type: BMBF project
  Project supervision: Dr.-Ing. Stephan Olbrich (RRZN), Dipl.-Phys. Hans-Christian Hege (ZIB)
  Duration: 01/01/2001 - 31/12/2002

  The goal of this project is to realize a tele-immersive, multi-modal virtual reality environment, which provides three-dimensional, collaborative presentation, exploration and discussion capabilities on the basis of 3D representations. Extensions for steering numerical simulations shall lead to a "Virtual Laboratory" scenario, which could be applied in the context of high performance computing, serving for several purposes, such as better understanding of complex, dynamic relationships, getting important design parameters of expensive or dangerous installations, or developing advanced educational technologies.

  Several partners are involved in this project in charge of the "Regionales Rechenzentrum für Niedersachsen" (RRZN) and the "Konrad-Zuse Zentrum für Informationstechnik" in Berlin (ZIB). Our special goal is the stereoscopic visualization of huge time-dependent data on a local workstation, which have been created on a remote massively parallel computer (in our case by the LES model PALM). In principle, state-of-the-art front-end graphic workstations and software are unable to handle such huge data sets (single scalar arrays may be as big as several Gigabyte). Our idea is to apply the postprocessing of the raw data into geometric 3D scenes (polygons, lines, or points) as part of the MPI-based parallel simulation. Only the geometric scenes are then transferred in a specially designed binary format to the local graphic workstation and visualized with the WEB-browser plugin DocShow-VR, developed at the RRZN.
   
   

• Development of a High Performance Parallel Large Eddy Simulation Model and its Application to the Atmospheric Boundary Layer
  Responsible: Prof. Yign Noh; PD Dr. Siegfried Raasch
  Project type: Joint project with the Yonsei University, Seoul, Prof. Yign Noh (jointly funded by DFG and KOSEF)
  Duration: 01/09/2000 - 31/08/2002

  This is a joint project together with the "Department of Atmospheric Sciences" at Yonsei University, South Korea. Its goal is the optimization of PALM for the efficient use on state-of-the-art parallel architectures (i.e. shared memory clusters like the IBM-Regatta) and its application to various problems of atmospheric and oceanic boundary layers (e.g. improvement of mixed layer parameterizations). The project permits the exchange of scientists for two months per year.
   
   

• Development of a Multigrid-Scheme in order to Solve Elliptic Differential Equations on Massivly Parallel Computers and its Implementation in the LES Model PALM
  Responsible: cand.met. Jörg Uhlenbrock
  Project type: Diploma thesis
  Duration: 07/08/2000 - 06/08/2001

  In the near future, computations with the LES-model PALM should also be done with an irregular (bottom) boundary condition (e.g. due to buildings). Thereafter, the modified model will be used for investigations of the tubulent flow structure in a simplified urban area. To solve the Boussinesq-approximated Navier-Stokes equations, the application of a so-called "pressure solver" is necessary after each timestep in the model, resulting in a windfield with no divergence. With regard to our model, the pressure solver is just a Poisson equation. In the actual model version the solution of the poisson equation is realized by a non-iterative procedure, based on Fast-Fourier Tansformation (FFT). But this method cannot be applied to an irregular boundary condition. For such a boundary, iterative procedures are more suitable, e.g. the Gauss-Seidel method. Furthermore, the iterative methods can easily be paralellized. Unfortunately, the convergence of these methods on large computational grids, as used by our model runs, is very slow. Therefore, the FFT has been the only practical method to solve the Poisson equation up to date. A realistic alternative is provided by the so-called multigrid method, which accelerates the convergence of iterative methods. The solution of the Poisson equation then becomes independent of grid size. The target of this diploma thesis is to develop a parallelized version of such a multigrid method for solving the Poisson equation, and its implementation in PALM.
   
   

• Large-Eddy Simulations of Thermally-Induced Circulations in the Convective Boundary Layer
  Responsible: cand.met. Marcus Oliver Letzel, MSc
  Project type: Diploma thesis
  Duration: 06/01/2000 - 13/02/2001

  Mesoscale circulations induced thermally by differential boundary layer heating due to surface inhomogeneities on scales of 10 km and more can significantly affect the average profiles and the structure of the atmospheric boundary layer. The inhomogeneities studied were one-dimensional and were represented in the model by sinusoidal surface heatflux variations. The results of this numerical study suggest that mesoscale circulations may considerably impede the typical quasi-steady convective boundary layer development.  The circulations are affected - often nonlinearly - by a number of parameters: Mean surface heatflux, perturbation wavelength and amplitude, subsidence rate, background wind magnitude and direction as well as the geographical latitude. The simulated mesoscale circulations were periodic, but asymmetric, which clearly shows up in form of higher wavenumber peaks in the power spectra of velocity and temperature. Vertical profiles and time series demonstrate that the onset of the mesoscale circulation triggers off a temporal boundary layer oscillation, whose period is proportional to the time that the inhomogeneous surface heatflux information takes to be advected from its minimum to its maximum and whose amplitude decreases with time due to friction. (See also the follow-up study by Herold and the studies by Schröter and Uhlenbrock.)
   
   

• First Attempts of the Validation of an LES Model by Acoustic Tomography Data
  Responsible: Dipl.-Met. Sonja Weinbrecht; Dipl.-Met. Marcus Oliver Letzel, MSc
  Project type: individual DFG project
  Duration: 15/06/1999 - 31/05/2003

  The aim of this project was to investigate turbulent convective structures near the surface by means of LES and acoustic tomography. So this was a cooperative project between the Institute of Meteorology, University of Leipzig and the Institute of Meteorology and Climatology, University of Hannover. By acoustic tomography (Acoustic Research Group at LIM) high resolution and volume-averaged data can be measured and compared directly with the high resolution and volume-averaged simulation data (our group). All simulations were run with our LES-model PALM.

  By comparing the simulation results with the measured data we tried to evaluate the LES-model PALM and wanted to test different subgrid-scale parametrization models implemented in the LES-model compare their results.

  In preparation of such a quantitative comparison first the sensitivity of the LES-model against the boundary conditions and the initial parameters was observed. We found that the simulations results are highly sensitive towards the surface roughness length (if the surface temperature is prescribed). With the help of the sensitivity study results it is now possible to name the measurement accuracies of the boundary conditions and initial parameters which are needed to perform a quantitative comparison. Furthermore the influence of measurement errors of these parameters on the simulation results can now be quantified.

  A first comparison with acoustic tomography data showed some differences which can be explained with the help of the sensitivity study and with inaccurate measurements of acoustic travel time and acoustic transmitter-receiver distances.

  To check the method of the acoustic tomography acoustic travel time measurements have been performed with the LES-model. So the simulated data could be compared with the simulated acoustic travel times which were analysed using the algorithms of the acoustic tomography method. With the help of this comparison some problems with the algorithm to separate the mean wind influence from the sonic speed were detected. These problems will be solved by using reciprocal acoustic travel time measurement methods. (See also the follow-up study by Weinbrecht.)
   
   

• Investigation of the Evolution of Organized Convection during a Cold Air Outbreak using a Parallelized Large-Eddy Simulation Model
  Responsible: Dipl.-Met. Michael Schröter
  Project type: individual DFG project
  Duration: 15/06/1998 - 14/06/2001

  During so called cold-air outbreaks cold and stably stratified air-masses are advected across relatively warm surfaces. The heating from below causes the development of a convective boundary layer in which a typical sequence of convection pattern can be observed: As soon as the cold air hits the warm surface, roll-like secondary flow pattern develop, appearing in satellite images as so called cloud-streets. Further downstream the roll pattern gradually changes to a hexagonal cellular convection pattern. While in classical laboratory experiments of Rayleigh-Benard convection the aspect ratios of the convection patterns are about 1:3, values up to 1:30 are typically observed during cold-air outbreaks. The aspect ratio is defined as the ratio between the wavelength or diameter of the pattern to their height. With boundary layer heights of 2 km, diameters of the convection pattern of about 60 km and more could be observed.

  Within the last two decades the phenomenon of cold-air outbreaks was increasingly studied using three-dimensional numerical models. These simulations suggested that adiabatic heat sources like latent heat release due to condensation are a condition precedent to observe large aspect ratios. Unfortunately, these simulations could not be carried out satisfactorily so far due to insufficient computer resources. To study the evolution of convective structures during cold-air outbreak situations the computational domains have to be large enough to contain the large cellular pattern, and they must have a spatial resolution fine enough in order to resolve smaller scales (single up- and downdrafts). Hence, the results of previous studies are afflicted with different uncertainties: Either the model domain was too small in order to allow a undisturbed cell growth or a too coarse resolution (up to 2 km) had to be used in order to be able to cover larger areas. Consequently it was unpossible to decide whether interactions between smaller and larger scales may affect the cell structure.

  For the first time today's massively parallel computers provide the possibility to perform simulations using large model domains and a fine grid-spacing simultaneously. Hence, the aim of this study was to apply a large-eddy simulation model (LES) that is specially designed for the use on massively parallel computers to cold-air outbreak situations to identify the physical processes which lead to the large aspect ratios observed during cold-air outbreak situations.

  This study removed the uncertainties of the earlier studies. Actually, strong evidence is given that diabatic heat sources are responsible for the existence of large aspect ratios. In contrast to earlier simulations it could be shown that cellular pattern also occur in the dynamic field variables. A further result of this study is that the numerically simulated role-like structures described so far in the literature were obviously due to a insufficient model resolution or unsuitable sub-grid parameterization. As a possible reason that convection rolls failed to appear in earlier simulations and in the simulations performed here, the non-consideration of the shear-increasing impact of spatially inclined boundary layer inversions was detected. (See also the study by Gryschka.)
   
   

• LES of the atmospheric boundary layer over water surfaces partially covered with sea-ice
  Responsible: Dipl.-Met. Guido Harbusch
  Project type: DFG project within the joint Antarctica Research Programme ("koordiniertes Programm Antarktisforschung")
  Duration: 01/07/1996 - 30/09/2000

  This project used PALM simulations to investigate how the turbulent structure of the atmospheric boundary layer is influenced by small scale surface inhomogeneities with typical diameters of about the boundary layer height z_i . The inhomogeneities were designed as discontinuous, chessboard-like variations of the surface heat flux that was prescribed as the bottom boundary condition. A large heat flux amplitude was chosen to create conditions typical of the Arctic or Antarctic marginal ice zone during cold air outbreaks. One main aim of this study was to determine the effects of such large heat flux variations and to describe the influence exerted by variations of incident flow speed and direction. Particular interest was paid to the inhomogeneity-induced secondary circulations that were analyzed using phase averages.

  Compared with continuous inhomogeneities of the same size, discontinous inhomogeneities principally cause similar, but much stronger effects. In contrast to a homogeneously heated boundary layer the horizontally averaged second and third moments are considerably affected by the inhomogeneities. Significant effects, however, only occur when the diameter of the inhomogeneities is at least as large as the height of the boundary layer. Then, especially the vertical energy transport increases, and the effects of the inhomogeneities start to show up even in the vertical temperature and heat flux profiles that don't exhibit the shapes typical of a homogeneous CBL any longer. The vertical gradient of potential temperature is slightly positive within the entire mixing layer, and the heat flux profile departs from its usual linear shape. These changes, though, are not due to the discontinuous form of the inhomogeneities but mainly due to the large heat flux amplitude.

  The structure of the secondary circulations, however, is very sensitive to the wavelength and form of the inhomogeneities as well as the heat flux amplitude, wind speed and direction. The main controlling parameter is the near-surface temperature distribution and hence the horizontal pressure gradient perpendicular to the mean flow direction. The secondary circulations vary from direct circulations with updraughts over the centers of the heated areas to rather indirect circulations with updraughts on both sides of the centers and downdraughts just above them. Roll-like circulation pattern occur for a background flow of more than 2.5 m/s.

  Previous studies often showed that even a moderate background flow of 5 m/s completely eliminates all potential effects of the surface inhomogeneities. In contrast, the present study demonstrated that the influence due to the increasing background flow strongly depend on the orientation of backgraound flow relative to the surface inhomogeneity. On the one hand, even under an incident flow of 7.5 m/s secondary circulations remain strong provided that the wind direction is parallel to the diagonal direction of the chess-board pattern. On the other hand, the effects of the inhomogeneities are considerably weakened even for background velocities as slow as 2.5 m/s provided that the wind vector of the backgroundflow is perpendicular to the side lines of the chess-board squares. (See also the studies by Letzel and Herold.)

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Links

• Upcoming meetings & conferences
  • 13th Conference on Cloud Physics, 28 June to 2 July, 2010 - Portland, OR, USA
  • 19th Symposium on Boundary Layer Turbulence of the American Meteorological Society, 2-6 August, 2010 - Keystone, CO, USA
  • 14th Conference on Mountain Meteorology, 30 August to 3 September, 2010 - Lake Tahoe Vicinity, CA, USA 
  • DACH 2010, 20-24 September, 2010 - Bonn, Germany

• Recent meetings & conferences
  
  • 7th International Conference on Urban Climate (ICUC-7) 29 June to 3 July, 2009 - Yokohama, Japan
  • Climate Analysis for Urban Planning: The 5th Japanese-German Meeting on Urban Climatology, 6-11 October 2008 - Freiburg, Germany
  • 18th Symposium of the American Meteorological Society (AMS) on Boundary Layers and Turbulence 9-13 June 2008 - Stockholm, Sweden
  • European Geosciences Union, General Assembly 2008 13-18 April, 2008  - Vienna, Austria
  • DACH 2007, 10-14 September 2007 - Hamburg, Germany
  • European Geosciences Union, General Assembly 2007 15-20 April, 2007  - Vienna, Austria
  • Geophysical Turbulence Program Workshop "Turbulence and Scalar Transport in Roughness Sublayers", 26-28 September 2006 - Boulder, Colorado, USA
  • 6th International Conference on Urban Climate (ICUC-6), 12-16 June, 2006 - Göteborg, Sweden
  • 6th Symposium on the Urban Environment, 86th Annual AMS Meeting, 28 January - 2 February 2006 - Atlanta, GA, USA
  • Climate Analysis for Urban Planning: The 4th Japanese-German Meeting on Urban Climatology, 30 November - 2 December 2005 - Tsukuba, Japan
  • European Meteorological Society, 5th Annual Meeting of the European Meteorological Society (EMS),
    7th European Conference on Applications of Meteorology (ECAM), 12-16 September 2005 - Utrecht, The Netherlands
  • European Geosciences Union, General Assembly 2005, 24-29 April 2005 - Vienna, Austria
  • DACH 2004, 7-10 Sep 2004 - Karlsruhe, Germany
  • 5th Symposium of the American Meteorological Society (AMS) on the Urban Environment 23-28 Aug 2004 - Vancouver, British Columbia, Canada
  • 16th Symposium of the American Meteorological Society (AMS) on Boundary Layers and Turbulence (16BLT) 9-13 August 2004 - Portland, ME, United States
  • 5th International Conference on Urban Climate (ICUC 5) of the International Association for Urban Climate (IAUC) 01-05 Sep 2003 at University of Lodz - Lodz, Poland
  • PALM seminar 08-14 July 2003 - Zingst, Germany
  • EGS-AGU-EUG Joint Assembly 06-11 Apr 2003 - Nice, France
  • Workshop: Quality Control of Eddy-Covariance Measurements 15-17 Nov 2002 at Thurnau, University of Bayreuth - Thurnau, Germany
  • 15th Symposium of the American Meteorological Society (AMS) on Boundary Layers and Turbulence 15-19 July 2002 at Wageningen University - Wageningen, The Netherlands

• Co-operating research groups
  • Germany
    • University of Hamburg, Environmental Wind Tunnel Laboratory (EWTL), Prof. Michael Schatzmann & Dr. Bernd Leitl
    • Leibniz Universität Hannover, Regional Computer Center for Lower Saxony (RRZN) and L3S Research Center, EVITA project group
    • Leibniz Universität Hannover, Institute of Cartography and Geoinformatics
      
    • University of Bayreuth, Department of Micrometeorology
    • University of Kassel, FB 6, Fachgebiet Umweltmeteorologie, AG Luft
    • Technical University of Braunschweig, Institute of Aerospace Systems, Helicopter-borne turbulence measurement system (HELIPOD)
    • University of Leipzig, Leipzig Institute for Meteorology (LIM), Acoustic Research Group
  • Norway
  • Nansen Environmental and Remote Sensing Center/Bjerknes Centre for Climate Research, affiliated with the University of Bergen, Dr. Igor Esau
  • Japan
    • Tokyo Institute of Technology, Department of International Development Engineering, Prof. Manabu Kanda
    • Ehime University, Shikoku, Department of Civil and Environmental Engineering, Prof. Ryo Moriwaki
    • Kyushu University, Fukuoka, Research Institute for Applied Mechanics (RIAM), Center for East Asian Ocean-Atmosphere Research, Numerical Modeling Group, Prof. Jong-Hwan Yoon
    • Kyushu University, Fukuoka, Urban and Architectural Environment Laboratory,  Interdisciplinary Graduate School of EngineeringSciences (IGSES), Prof. Aya Hagishima
  • Korea
    • Yonsei University (Seoul), Department of Atmospheric Sciences, Prof. Yign Noh
    • Seoul National University, School of Earth and Environmental Sciences, Convection and Urban Meteorology Group, Prof. Jong-Jin Baik
  • Hong Kong
    
    • The Chinese University of Hong Kong, Department of Architechture, Prof. Edward Ng

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Reviewed publications (under participation) of the PALM group since 1997 in chronological order:

Foken, T., M. Mauder, C. Liebethal, F. Wimmer, F. Beyrich, J.-P. Leps, S. Raasch, H. A. R. DeBruin, W. M. L. Meijninger and J. Bange, 2010: Energy balance closure for the LITFASS-2003 experiment, Theor. Appl. Clim.,  101, 149-160, doi:10.1007/s00704-009-0216-8.

Noh, Y.,  G. Goh,  S. Raasch and M. Gryschka, 2009: Formation of a diurnal thermocline in the ocean mixed layer simulated by LES, J. Phys. Oceanogr., 39, 1244-1257.

Markkanen, T., G. Steinfeld, N. Kljun, S. Raasch and T. Foken, 2009: Comparison of conventional Lagrangian stochastic footprint models against LES driven footprint estimates, Atmos. Chem. Phys., 9, 5575-5586, http://www.atmos-chem-phys.net/9/5575/2009/

Gryschka, M., C. Drüe, D. Etling and S. Raasch, 2008: On the influence of sea-ice inhomogeneities onto roll convection in cold-air outbreaks, Geophys. Res. Lett., 35, L23804, doi:10.1029/2008GL035845.

Gryschka, M.,  B. Witha and D. Etling, 2008: Scale Analysis of Convective Clouds,  Meteorol. Z., 17, 785-791.

Steinfeld, G., S. Raasch and T. Markkanen, 2008: Footprints in homogeneously and heterogeneously driven boundary layers derived from a Lagrangian stochastic particle model embedded into large-eddy simulation, Boundary-Layer Meteorol., 129, 225-248.

Letzel, M.O., M. Krane and S. Raasch, 2008: High resolution urban large-eddy simulation studies from street canyon to neighbourhood scale, Atmos. Env., 42, 8770-8784, doi:10.1016/j.atmosenv.2008.08.001.

Lüpkes C., V. Gryanik, B. Witha, M. Gryschka, S. Raasch and T. Gollnik, 2008: Modeling convection over arctic leads with LES and a non-eddy-resolving microscale model, J. Geophys. Res., 113, C09028, doi:10.1029/2007JC004099. 

Letzel, M. O., G. Gaus, S. Raasch, N. Jensen and M. Kanda, 2008: Turbulent flow around high-rise office buildings in downtown Tokyo. Dynamic Visualization in Science, http://www.dyvis.org/DyVis?Sig=13100.

Steinfeld, G., M. O. Letzel, S. Raasch, M. Kanda and A. Inagaki, 2007: Spatial representativeness of single tower measurements and the imbalance problem with EC fluxes - results of an LES study, Boundary-Layer Meteorol., 123, 77-98. doi:10.1007/s10546-006-9133-x

Bange, J., P. Zittel, T. Spieß, J. Uhlenbrock and F. Beyrich, 2006: A New Method for the Determination of Area-Averaged Turbulent Surface Fluxes from Low-Level Flights Using Inverse Models. Boundary-Layer Meteorol., 119, 527-561.

Noh, Y., Kang, I.S., Herold, M. and S. Raasch, 2006: Large Eddy Simulation of Particle Settling in the Ocean Mixed Layer. Phys. of Fluids, 18, 085109.

Beare, R.J, M.A.J. Cortes, J. Cuxart, I. Esau, C. Golaz, A.A.M. Holtslag, M. Khairoutdinov, B. Kosovic, D. Lewellen, T. Lund, J. Lundquist, A. Mccabe, M.K. Macvean, A. Moene, Y. Noh, G. Poulos, S. Raasch and P. Sullivan, 2006: An Intercomparison of Large-Eddy Simulations of the Stable Boundary Layer. Boundary-Layer Meteorol., 118, 247-272.

Mengelkamp, H.-T., F. Beyrich, G. Heinemann, F. Ament, J. Bange, F. Berger, J. Bösenberg, T. Foken, B. Hennemuth, C. Heret, S. Huneke, K.-P. Johnsen, M. Kerschgens, W. Kohsiek, J.-P. Leps, C. Liebethal, H. Lohse, M. Mauder, W. Meijninger, S. Raasch, C. Simmer, T. Spieß, A. Tittebrand, J. Uhlenbrock and P. Zittel, 2006: Evaporation Over a Heterogeneous Land Surface: The EVA-GRIPS Project. Bull. Amer. Meteor., Soc., 87, 775-786.

Inagaki, A., M.O. Letzel, S. Raasch and M. Kanda, 2006: Impact of surface heterogeneity on energy imbalance: a study using LES. J. Meteor. Soc. Japan, 84, 187-198. doi:10.2151/jmsj.84.187

Gryanik, V., J. Hartmann, S. Raasch and M. Schröter, 2005: A Refinement of the Millionshchikov Quasi-Normality Hypothesis for Convective Boundary Layer Turbulence. J. Atmos. Sci., 62, 2632-2638.

Gryschka, M. and S. Raasch, 2005: Roll Convection During a Cold Air Outbreak: A Large Eddy Simulation with Stationary Model Domain. Geophys. Res. Lett., 32, L14805, doi:10.1029/2005GL022872.

Raabe, A., K. Arnold, A. Ziemann, F. Beyrich, J.-P. Leps, J. Bange, P. Zittel, T. Spiess, T. Foken, M. Göckede, M. Schröter and S. Raasch, 2005: STINHO - Structure of Turbulent Transport Under Inhomogeneous Surface Conditions - Part 1: The Micro-a Scale Field Experiment. Meteorol. Z., 14, 315-327.

Schröter, M., S. Raasch and H. Jansen, 2005: New Results on the Cell Broadening Problem during Cold Air Outbreaks from High Resolution Large-Eddy Simulations. J. Atmos. Sci., 62, 2023-2032.

Kanda, M., A. Inagaki, M.O. Letzel, S. Raasch and T. Watanabe, 2004: LES Study of the Energy Imbalance Problem with Eddy Covariance Fluxes. Boundary-Layer Meteorol., 110, 381-404. doi:10.1023/B:BOUN.0000007225.45548.7a

Kim, H.-J., Y. Noh and S. Raasch, 2004: Interaction between wind and temperature fields under the heterogeneous heat flux in the planetary boundary layer. Boundary-Layer Meteorol., 111, 225-246.

Min, H.S. and Y. Noh, 2004: Influence of the Surface Heating on Langmuir Circulation. J. Phys. Oceanogr., 34, 2630-2641.

Noh, Y., H.S. Min and S. Raasch, 2004: Large Eddy Simulation of the Ocean Mixed Layer: the Effects of Wave Breaking and Langmuir Circulation. J. Phys. Oceanogr., 34, 720-735.

Weinbrecht, S., S. Raasch, A. Ziemann, K. Arnold and A. Raabe, 2004: Comparison of Large-Eddy Simulation data with spatially averaged measurements obtained by Acoustic Tomography - presuppositions and first results. Boundary-Layer Meteorol., 111, 441-465.

Etling, D. and S. Weinbrecht, 2004: Organized structures in the atmospheric boundary layer. In: Shallow Flows (G. Jirka, W. Uijttewal, Eds.), Balkema, London, 157-162.

Inagaki, A., M. Kanda, M.O. Letzel and S. Raasch, 2003: LES Study of the Energy Imbalance Problem for Heterogeneous Surface (in Japanese). Annual J. Hydraulic Eng., JSCE, 47, 37-42.

Letzel, M.O. and S. Raasch, 2003: Large-Eddy Simulation of Thermally Induced Oscillations in the Convective Boundary Layer. J. Atmos. Sci., 60, 2328-2341. doi:10.1175/1520-0469(2003)060<2328:LESOTI>2.0.CO;2

Noh, Y., W.-G. Cheon, S.-Y. Hong and S. Raasch, 2003: Improvement of the K-Profile Model for the Planetary Boundary Layer based on Large Eddy Simulation Data. Boundary-Layer Meteorol., 107, 401-427.

Noh, Y., W.-G. Cheon and S. Raasch, 2003: The Role of Preconditioning in the Evolution of Open-Ocean Deep Convection. J. Phys. Oceanogr., 33, 1145-1166.  (selected among "Papers of note" in the Bull. Amer. Meteor. Soc., 84, 574-575, in May 2003)

Etling, D., G. Harbusch and B. Brümmer, 2002: Large-Eddy Simulation of an off-ice airflow during BASIS. Boreal Env. Res., 7, 225-228.

Kanda, M., M.O. Letzel, A. Inagaki and S. Raasch, 2002: Investigation on Spatial Representativeness of Point Measurements - Implication for Imbalance Problem (in Japanese). Annual J. Hydraulic Eng., JSCE, 46, 97-102.  (awarded the Best Paper Price of the 46^th "Suiko" Conference (Water Civil Engineering) in Nagoya, Japan, by the Japan Society of Civil Engineers on 12 March 2002)

Kanda, M., T. Watanabe, M.O. Letzel and S. Raasch, 2002: LES Study on the Energy Imbalance Problem with Eddy Covariance Fluxes. I. Analysis for Convective Boundary Layers (in Japanese).  J. Japan Soc. Hydro. Water Res., 15, 243-252.

Letzel, M.O. and S. Raasch, 2002: Large-Eddy Simulation of Thermally Induced Oscillations in the Convective Boundary Layer. Annual J. Hydraulic Eng., JSCE, 46, 67-72.

Olbrich, S., H. Pralle and S. Raasch, 2001: Using streaming and parallelization techniques for 3D visualization in a high-performance computing and networking environment. Lecture Notes in Computer Science, 2110, 231-240.

Raasch, S. and G. Harbusch, 2001: An Analysis of Secondary Circulations and their Effects Caused by Small-Scale Surface Inhomogeneities Using Large-Eddy Simulation. Boundary-Layer Meteorol., 101, 31-59.

Raasch, S. and M. Schröter, 2001: A Large-Eddy Simulation Model performing on Massively Parallel Computers. Meteorol. Z., 10, 363-372.

Weinbrecht, S. and S. Raasch, 2001: High Resolution Simulations of the Turbulent Flow in the Vicinity of an Arctic Lead. J. Geophys. Res., 106 C11, 27035-27046.

Schröter, M., J. Bange and S. Raasch, 2000: Simulated Airborne Flux Measurements in a LES Generated Convective Boundary Layer. Boundary-Layer Meteorol., 95, 437-456.

Raasch, S. and D. Etling, 1998: Modeling Deep Ocean Convection: Large Eddy Simulation in Comparison with Laboratory Experiments. J. Phys. Oceanogr., 28, 1786-1802.

Hartmann, J., C. Kottmeier and S. Raasch, 1997: Roll Vortices and Boundary-Layer Development During a Cold Air Outbreak. Boundary-Layer Meteorol., 84, 45-65.

Recent work submitted for publication:

Letzel, M.O., C. Helmke, E. Ng, X. An and S. Raasch, 2010: LES study on pedestrian level ventilation in Hong Kong. Building and Environment, submitted.

Noh, Y., G. Goh and S. Raasch, 2010: Examination of the Mixed Layer Deepening Process during Convection Using LES. J. Phys. Oceanogr., accepted.

Markkanen, T., G. Steinfeld, N. Kljun, S. Raasch and T. Foken, 2010: A numerical case study on footprint model performance under inhomogeneous flow conditions. Meteorol. Z., accepted.

Selected conference abstracts:

• 18th Symposium of the American Meteorological Society (AMS) on Boundary Layers and Turbulence 9-13 June 2008 - Stockholm, Sweden:
• Franke, T. and S. Raasch, 2008: Large-eddy simulation of dust devils in the atmospheric boundary layer.
• Steinfeld, G., S. Raasch, T. Markkanen, and T. Foken, 2008: Evaluation of footprints in homogeneous and inhomogeneous terrain with a Lagrangian stochastic particle model embedded into a large eddy simulation model.
• Witha, B. and S. Raasch, 2008: The effect of leads in the sea-ice on the Antarctic boundary layer: a high-resolution study using a parallelized LES model.
• 28th Conference on Agricultural and Forest Meteorology 28 April - 2 May 2008 - Orlando, FL, USA:
• Markkanen, T., G. Steinfeld, S. Raasch and T. Foken, 2008: Footprint model performance under inhomogeneous flow conditions.
• European Geosciences Union, General Assembly 2008 13-18 April, 2008  - Vienna, Austria:
• Esau, I., M.O. Letzel, and S. Raasch, 2008: First results from coupled atmosphere-ocean large-eddy simulations.
• 24th International Conference on Passive and Low Energy Architecture (PLEA 2007) 22-24 November 2007 - Singapore:
• Letzel, M. O., X. An, and E. Ng, 2007: Modelling the air flows in Urban Places in Hong Kong using Large-Eddy Simulation, 615-619.
• DACH 2007, 10-14 September 2007 - Hamburg, Germany:
• Franke, T. and S. Raasch, 2007: Numerische Simulation von Staubteufeln in der atmosphärischen Grenzschicht.
• Katzschner, L. and Letzel, M.O., 2007: Stadtklimaanalyse Hong Kong mittels LES Modellierungen und Messkampagnen zur Ermittlung stadtplanerischer Hinweise.
• Letzel, M.O. and S. Raasch, 2007: Hochauflösende Grobstruktursimulation turbulenter Gebäudeumströmung.
• Steinfeld, G., S. Raasch, T. Markkanen and T. Foken, 2007: Bestimmung von Konzentrations- und Flussfootprints mit einem durch LES-Daten angetriebenen Lagrangeschen stochastischen Partikeldispersionsmodell.
• Witha, B., S. Raasch and C. Lüpkes, 2007: Untersuchung des Einflusses von Eisrinnen auf die antarktische Grenzschicht.
• 6th International Conference on Urban Climate (ICUC-6) 12-16 June, 2006 - Göteborg, Sweden:
• Letzel, M.O., M. Kanda and S. Raasch, 2006: A new dimension of Urban Climate Modelling with Parallel Large-eddy Simulation, 296-299.
• European Geosciences Union, General Assembly 2006, 02-07 April 2006 - Vienna, Austria:  
• Steinfeld, G., S. Raasch, M. O. Letzel, M. Kanda and A. Inagaki, 2006: LES study on the imbalance problem.
• 6th Symposium on the Urban Environment, 86th Annual AMS Meeting, 28 January - 2 February 2006 - Atlanta, GA, USA:
• Inagaki, A., G. Steinfeld, S. Raasch and M. Kanda, 2006: The numerical experiment of the energy and CO₂ imbalance problem using LES.
• Climate Analysis for Urban Planning: The 4th Japanese - German Meeting on Urban Climatology, 30 November - 2 December 2005 - Tsukuba, Japan:
• Letzel, M.O., M. Kanda and S. Raasch, 2005: A new dimension of Urban Climate Modelling with Parallel Large-eddy Simulation.
• Korean Meteorological Society, Proceedings of the Spring Meeting:
• Raasch, S., 2005: High Resolution Large Eddy Simulations on the Effects of Land Surface Heterogeneities, 6-9.
• European Meteorological Society, 5th Annual Meeting of the European Meteorological Society (EMS),
  7th European Conference on Applications of Meteorology (ECAM), 12-16 September 2005 - Utrecht, The Netherlands:
• Jansen, H. and S. Raasch, 2005: Investigations on Mesoscale Cellular Convection with
  High Resolution Large Eddy Simulations.
• European Geosciences Union, General Assembly 2005, 24-29 April 2005 - Vienna, Austria:
• Gryschka, M., S. Raasch, and D. Etling, 2005: Large Eddy Simulation of a Cold Air Outbreak with Stationary Model Domain. Geophysical Research Abstracts, 7, 09780.
• Jansen, H., M. Schröter, S. Raasch and I.-S. Kang, 2005: The influence of background wind on aspect ratios of convective cells during cold air outbreaks - Studies with a large eddy simulation model.
• Deutsch-Österreichisch-Schweizerische Meteorologen-Tagung (DACH 2004) 7-10 Sep 2004 - Karlsruhe, Germany:
• Gryschka, M. and S. Raasch, 2004: Grobstruktursimulation eines Kaltluftausbruches mit stationärem Modellgebiet.
• Jansen, H., M. Schröter and S. Raasch, 2004: Modellstudien zu Aspektverhältnissen bei Kaltluftausbrüchen.

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Last update: 26 May, 2010     Please email suggestions or comments concerning this page to Siegfried Raasch (see members).

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