High-resolution sensitivity studies withe the regional climate model COSMO-CLM [Elektronische Ressource] / von Cathérine Meißner

Meissner

Informations

• Publié par: karlsruher_institut_fur_technologie
• Publié le: 01 janvier 2008
• Nombre de lectures: 10
• Langue: English
• Poids de l'ouvrage: 24 Mo

Extrait

HIGH-RESOLUTION SENSITIVITY STUDIES WITH
THE REGIONAL CLIMATE MODEL COSMO-CLM





Zur Erlangung des akademischen Grades eines
DOKTORS DER NATURWISSENSCHAFTEN
von der Fakultät für Physik der Universität (TH)
Karlsruhe


genehmigte


DISSERTATION


von


Dipl.-Met. Cathérine Meißner
aus
Achern




Tag der mündlichen Prüfung: 08. Februar 2008
Referent: Prof. Dr. Christoph Kottmeier
Korreferent: Prof. Dr. Sarah Jones
Abstract

High-resolution regional ensemble climate simulations with the regional climate model
COSMO-CLM are performed for Southwest Germany to study the sensitivity of meteoro-
logical and hydrological variables to simulation set-up, including the domain size, driving
data, horizontal resolution and physical parameterisations and parameter settings. The
model setup found adequate for such simulations is a domain including the Alps, ERA-40
reanalysis data as driving data, and a horizontal resolution of 7 km. The sensitivity of
simulation results to a changed model setup is highest for the change in driving data and is
higher in winter than in summer.
This adequate model setup is used to investigate the influence of the land surface scheme
on COSMO-CLM simulations. The standard land surface scheme TERRA_LM is replaced
by the land surface scheme VEG3D, which contains an explicit vegetation layer. Stand-
alone simulations with both land surface schemes show better agreement with observations
for the VEG3D scheme, especially over high vegetation. Coupled online with the
COSMO-CLM, both schemes yield similar results on the spatial patterns of the meteoro-
logical variables but the absolute values may differ considerably. No model system gives
better results than the other for 2m-temperature and precipitation compared to observa-
tions, and the difference in TERRA_LM and VEG3D simulation is similar to the differ-
ence obtained by changing other physical parameterisations or the time-integration
scheme. Freezing and melting processes in the soil are implemented in VEG3D to make
the scheme applicable for climate simulations. Stand-alone simulations with the new
scheme yield better results than those without the consideration of freezing and melting
processes. Better results in stand-alone simulations are obtained when using different soil
types within one soil column, instead of using one single soil type for the whole column.
Therefore, a soil type inventory for Germany for the coupled model system COSMO-
CLM/VEG3D is provided in this thesis, which contains several soil types within one soil
column.
A strategy for a statistical-dynamical downscaling method is developed and evaluated to
replace time consuming day by day simulations. The method shows the ability to yield
results similar to those of the continuous simulation.



CONTENTS
1 Introduction 1
2 Regional climate models and simulations 6
3 Description of the COSMO model 12
3.1 Dynamics.................................................................................................................. 13
3.1.1 Model equations.............................................................................................. 13
3.1.2 Rotated coordinate system.............................................................................. 16
3.1.3 Terrain following coordinates......................................................................... 17
3.2 Numerics 18
3.2.1 Grid structure .................................................................................................. 18
3.2.2 Time integration.............................................................................................. 19
3.3 Initial and boundary conditions................................................................................ 20
3.4 Physical parameterisations ....................................................................................... 21
4 Sensitivity studies 23
4.1 Simulation Setup ...................................................................................................... 25
4.2 Sensitivity studies for the whole simulation area..................................................... 28
4.2.1 Influence of driving data and horizontal resolution........................................ 28
4.2.2 Influence of initialisation................................................................................ 33
4.3 Sensitivity studies for Southwest Germany ............................................................. 36
4.3.1 Influence of simulation area ........................................................................... 36
4.3.2 Influence of horizontal resolution and driving data........................................ 39 II Contents

4.3.3 Sensitivity with respect to varying parameterisations, adjustable
parameters, and initialisation...........................................................................45
4.3.4 Comparison of observed and modelled trends of near-surface
temperature between 1991 and 2000...............................................................53
4.4 Summary...................................................................................................................54
5 Application and improvement of the land-surface scheme VEG3D 56
5.1 Parameterisation of freezing and melting processes in the soil ................................56
5.1.1 Calculation of soil temperature in frozen soil .................................................57
5.1.2 Parameterisation of soil water transport in frozen soil....................................59
5.1.3 Energy exchange during freezing and melting processes in the soil...............60
5.1.4 Evaluation of freezing and melting parameterisation in the soil.....................61
5.2 Variable soil types within one soil column...............................................................67
5.2.1 Simulations with the VEG3D stand-alone model for vertically
changing soil type............................................................................................68
5.2.2 Soil type map for COSMO-CLM simulations with different soil
types within one soil column...........................................................................71
5.3 Implementation of VEG3D in COSMO-CLM .........................................................73
5.3.1 New parameter data sets..................................................................................73
5.3.2 Coupling of VEG3D with the atmospheric part of the model.........................76
6 Sensitivity of COSMO-CLM regional climate simulations with respect to
VEG3D and TERRA_LM land surface scheme 78
6.1 Description of the models .........................................................................................80
6.1.1 TERRA_LM....................................................................................................80
6.1.2 VEG3D............................................................................................................83
III

6.2 Simulations with the stand-alone versions of the two soil-vegetation models ........ 87
6.2.1 Simulations for the Lindenberg grassland site................................................ 90
6.2.2 Simulations for the Hartheim forest site......................................................... 94
6.3 Daily simulations with the online coupled land surface schemes............................ 97
6.4 Simulations with the two land surface schemes coupled online with
COSMO-CLM for the year 2001 ........................................................................... 106
6.4.1 Comparisons for the whole investigation area.............................................. 107
6.4.2 Comparisons with data from observation sites............................................. 111
6.5 Long-term evaluation ............................................................................................. 114
6.5.1 Evaluation for the period from 1991 to 1995 ............................................... 115
6.5.2 Evaluation for the period from 1991 to 2000 117
6.6 Summary ................................................................................................................ 122
7 Statistical-dynamical downscaling 124
7.1 Influence of initial soil moisture and soil temperature profiles on
COSMO-CLM simulations .................................................................................... 124
7.2 Comparison of dynamical and statistical-dynamical downscaling for the
year 2001 ................................................................................................................ 131
7.2.1 Using Self-Organizing Maps for statistical-dynamical downscaling ........... 131
7.2.2 Comparison of the two different downscaling techniques for the
year 2001 ...................................................................................................... 133
7.2.2.1 Comparison of the results of the two downscaling schemes
for annual mean 2m-temperature.........................