Documentation of the Changes in the COSMO-Model
from Version 4.2 to 4.11

11.05.2010

In the following, the main changes for the COSMO-Model between Version 4.2 and Version 4.11 are briefly documented. For more comprehensive explanations take a look to the file misc.global, which is distributed with the COSMO-Model source code. Also, only the most important Namelist changes are described here. For a full documentation please refer to the User Guide.

Contents:

  1. Technical Changes
  2. Changes in the Dynamics
  3. Changes in the Physics
  4. Changes in the Diagnostics
  5. Changes in the Assimilation
  6. Further developments still under testing
  7. Brief description of new and changed Namelist Variables
  8. Changes of Results

1. Technical Changes

With COSMO_ART and the necessity to have some vector processor specific (or NEC-SX specific) optimizations, we implemented more ifdef-directives to the COSMO-Model. If you want to run the corresponding features, you have to define the appropriate directives before compiling the program.

Because of introducing more ifdefs, we changed the suffix of the main program again to be lmorg.f90 (in the last versions it was lmorg.F90). For a successful compilation of the COSMO-Model (no matter whether you use some of the ifdef variables or not), you have to use the preprocessor of your compiler in any case.

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2. Changes in the Dynamics

New (alternative) reference atmosphere
(by Günther Zängl; Version 4.8)

A new (alternative) reference atmosphere has been introduced, which is based on the temperature profile

T0(z) = T00 + delta_t EXP(-z/h_scal),

with default values of T00 = 213.15 K, delta_t = 75 K and h_scal = 10 km; (in the model code, T00 = t0sl - delta_t).

Thus, the reference atmosphere approaches an isothermal profile in the stratosphere, whereas the existing reference profile has an increasingly negative vertical temperature gradient in the stratosphere. The vertical extent of the model domain is no longer limited with the new reference atmosphere.

Except for idealized simulations, the reference atmosphere can only be chosen in INT2LM (from Version 1.9 on). All parameters of the reference atmosphere are coded in the GRIB/NetCDF records, and the COSMO-Model determines the type of reference atmosphere by decoding the GRIB/NetCDF records.

The following holds right now (might be changed in the future to account for additional vertical coordinate types):

The new reference atmosphere needs 2 additional parameters, which are also coded in the GRIB/NetCDF records:

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Potential temperature as advected variable in the Runge-Kutta dynamics
(by Günther Zängl; Version 4.9)

An option for using potential temperature as advected variable has been implemented in the Runge-Kutta scheme. The default still is using perturbed temperature.

A new Namelist variable itheta_adv has been introduced in /DYNCTL/ to choose the desired option:

  1. use perturbation temperature (T') for advection (default)
  2. use perturbation potential temperature (theta')
  3. use full potential temperature (theta)

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Generalized Asselin filter in the Leapfrog dynamics
(by Günther Zängl, based on the work of Williams 2009; Version 4.11)

An option to use a generalized Asselin Filter has been introduced. A new Namelist variable alphaass has been implemented for that. With the default value (1.0) the same results as before are obtained.

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3. Changes in the Physics

Introduction of an online coupling of aerosols and reactive tracers: COSMO-ART
(by Karlsruhe Institute of Technology; Version 4.9)

COSMO_ART is a chemistry package to compute aerosols and reactive tracers. It also includes a package to use pollen as tracers. The work of implementing COSMO_ART into the COSMO-model has been done by the group of Bernhard Vogel at the Karlsruhe Institute of Technology.

The COSMO-Model has been adapted to include this package via online coupling into its meteorology. The setup of the model, the I/O-module and the dynamics have been adapted to work with the additional variables.

COSMO_ART is implemented using ifdef-statements. Therefore COSMO_ART or the Pollen part have to be activated at compile time with the preprocessor directives -DCOSMOART or -DPOLLEN, resp. If these directives are not set, no change to the COSMO-Model is done.

There are 3 new Namelist switches in /RUNCTL/: with l_cosmo_art and l_pollen, resp., the execution of COSMO_ART can be controlled. In addition, with ldebug_art, a debug mode for COSMO_ART can be activated. The default for all these variables is .FALSE.

The COSMO_ART package itself is NOT part of the COSMO-Model. For accessing the source code for COSMO_ART, please contact the Karlsruhe Institute of Technology directly.

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Introduction of the sub-grid scale orography scheme
(by Jan-Peter Schulz; Version 4.5)

The sub-grid scale orography (SSO) scheme by Lott and Miller (1997) has been implemented in the COSMO-Model. It is also included in the DWD global model and works here well. The scheme deals explicitly with a low-level flow which is blocked when the sub-grid scale orography is sufficiently high. For this blocked flow separation occurs at the mountain flanks, resulting in a form drag. The upper part of the low-level flow is lead over the orography, while generating gravity waves. Verification at DWD had shown that the forecasted surface pressure in the COSMO-EU model shows a systematic bias. In particular, in wintertime high pressure systems tend to develop a positive pressure bias, by 1-2 hPa after 48h, low pressure systems a negative bias ("highs too high, lows too low"). Assumed causes are an underestimation of the cross-isobar flow in the PBL, caused by too little surface drag or too weak blocking at the orography. Tests with an envelope orography which exhibits considerably higher values in the mountains have shown a high sensitivity of the model to this change in orography with respect to the blocking of cyclones. Consequently, low pressure systems were filled more efficiently, the negative pressure bias was reduced. But an obvious disadvantage of the envelope orography is that the precipitation fields are altered in an unfavourable way. An alternative way to increase the surface drag and the blocking while not altering the precipitation fields is the use of an SSO scheme.

New Namelist switches:

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Introduction of the sea-ice scheme
(by Jan-Peter Schulz; Version 4.10)

The sea-ice model, that is already used in DWD's global model GME has been implemented into the COSMO-Model.

New Namelist switch:

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Modifications in the Tiedtke convection scheme
(by Dmitrii Mironov; Version 4.3)

A number of changes in the Tiedtke cumulus convection scheme, that are related to the treatment of convective cloud condensate as a mixed water-ice phase and of detrained convective cloud condensate are made.

These are

The fraction of cloud ice is computed as a function of temperature. The lower and the upper bounds of the temperature range, where convective cloud water and convective cloud ice are allowed to co-exist and the form of the interpolation function are the same as in the ECMWF IFS (IFS Documentation 2006).

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Modifications in the TKE scheme
(by Matthias Raschendorfer, Oliver Fuhrer; Version 4.10)

The following changes were implemented in the TKE scheme

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4. Changes in the Diagnostics

Additional options to calculate the 2m temperature
(by Matthias Raschendorfer; Version 4.3/4.8)

In the surface scheme, the interpolation onto diagnostic levels has changed, in particular it is now done without an exponential canopy profile, but with a diagnostic Prandtl layer interpolation even for scalars, using an adopted canopy layer resistance. This measure changes the values of the 2m temperature.

NOTE:
Because the 2m-temperature is also used in the soil model, these changes also influence the results of the forecast.

To choose also the old computation of the 2m temperature, a new Namelist switch itype_diag_t2m has been introduced:

  1. New computation with an exponential canopy profile, but with a diagnostic Prandtl layer interpolation even for scalars, using an adopted canopy layer resistance. (Default)
  2. Old computation with exponential canopy profile

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Additional options to calculate wind gusts
(by MCH; Version 4.8)

Several options have been implemented to compute the wind gusts. To choose a special option, a new Namelist switch itype_diag_gusts has been introduced:

  1. Dynamical gust derived from lowest model layer
  2. Dynamical gust derived from 30 m
  3. Computation of dynamical gust after Brasseur

The computation of the gust has been splitted into a dynamical and a convective gust (with corresponding fields and output variables vgust_dyn and vgust_con). vmax_10m still is the combination of both.

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5. Changes in the Assimilation

Reading observation data from NetCDF files
(by Christoph Schraff; Version 4.5)

A new interface has been introduced to read and pre-process observation data from NetCDF files instead of an AOF file. These NetCDF files are obtained by simple conversion from BUFR files which contain BUFR reports according to Table Driven Code Formats (TDCF) of WMO (see http://www.wmo.int/pages/prog/www/WMOCodes/OperationalCodes.html, http://www.wmo.int/pages/prog/www/WMOCodes/TemplateExamples.html) for those data types where TDCF have been defined, namely for SYNOP, SHIP, PILOT and TEMP types, but also for BUOY and AMDAR. For ACARS, BUFR from ARINC Centre 56 (USA) and from UK Met Office can be read, or alternatively, a combined format. For wind profiler, RASS, and VAD radar wind, a format defined by DWD is read, since there is no standard format defined by WMO yet. The names of the input files, that can already be used, are:

Other input files cannot yet be used. If a file is empty, it should be removed.

From which files the observations are read is controlled by the 2 Namelist variables (in the group NUDGING):

Name Meaning Default
itype_obfile to determine, from which file(s) the observations are read
  • 1: read observations from AOF
  • 2: read observations from NetCDF files
 1
ycdfdir directory in which the NetCDF input observation files reside ./

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6. Further Developments still under Testing

The multi-layer snow model
(by Ekaterina Machulskaya; Version 4.11)

A new multi-layer snow model has been implemented in src_soil_multlay.f90. This model is still under testing and it is not recommended to use it right now. More information will be given, once the tests have proceeded.

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Use of additional External Parameters
(by Jürgen Helmert; Version 4.11)

Additional external parameter fields have been introduced for

The use of these additional parameters is still under testing. The corresponding parameters are not yet included in the external parameter files distributed by DWD. More information will be given, once the tests have proceeded.

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7. Summary of new and changed Namelist Variables

There were the following changes for the Namelist variables:

Group Name Meaning Default
/RUNCTL/ itype_timing To specify, how a timing of the program should be done:
  1. output hourly timings per task
  2. output timings per task, summed up over all hours
  3. output hourly mean values for all tasks
  4. output mean values for all tasks, summed up over all hours
 4
ltime_mean
ltime_proc		 These variables have been eliminated. They are replaced by itype_timing -
itype_calendar To specify, which calendar is used during the forecast
  1. Gregorian calendar
  2. Every year has 360 days
 1
lyear_360 This variable has been eliminated. It is replaced by itype_calendar -
lcori, lmetr
lradlbc		 These variables have been moved to the group /DYNCTL/. -
lartif_data This variable has been moved from group /IOCTL/ (where it was named lgen to the group /RUNCTL/. -
l_cosmo_art Main switch to activate the COSMO-ART. .FALSE.
l_pollen Main switch to activate the Pollen Module. .FALSE.
ldebug_art To switch on/off the debug output for the ART / Pollen module. .FALSE.
/DYNCTL/ itheta_adv Option for using potential temperature as advected variable in the Runge-Kutta scheme:
  1. Use perturbation of temperature (T') for advection.
  2. Use perturbation of potential temperature (theta') for advection.
  3. Use full potential temperature (theta) for advection.
 0
alphaass Weight for Williams 2009 modification to the Asselin time-filter. (0.5 < alphaass <= 1.0) 1.0
lcori, lmetr
lradlbc		 These variables have been moved from /RUNCTL/ to the group /DYNCTL/. -
itype_lbcqx This variable has been renamed to itype_outflow_qrsg for a more meaningful name. -
itype_outflow_qrsg To choose the type of relaxation treatment for qr, qs, qg.
  1. qr, qs, qg are treated with the same lateral boundary relaxation as the other variables.
  2. No relaxation of qr, qs, qg is done at outflow boundary points.
 1
itype_lbc_qrsg To choose the type of lateral boundary treatment for qr, qs, qg, i.e., which values are used at the boundary zone:
  1. A zero-gradient condition is used for qr, qs, qg.
  2. qr, qs, qg are set to 0.0 at the boundary zone.
  3. No presetting is done at all at the boundary zone.
 1
/PHYCTL/ lsso Main switch to include subgrid scale orography processes. .FALSE.
nincsso Interval (in time steps) between two calls of the SSO scheme. 5
lseaice Main switch to switch on/off the sea ice scheme. .FALSE.
lemiss Option, to use an external surface emissivity map (if set to .TRUE.). If lemiss} is .FALSE. (default), a constant surface emissivity is assumed. .FALSE.
lstomata Switch to use a minimum stomata resistance map for plants. .FALSE.
itype_aerosol Switch to choose the type of aerosol map:
  1. Tanre. Constant aerosol distributions are given for rural, urban, desert areas and the sea.
  2. Tegen. A monthly aerosol climatology is used for sulfate drops, total dust, organic, black carbon and sea salt.
 1
itype_root Switch to select the type of root distribution:
  1. Uniform.
  2. Exponential (following Arora and Boer, 2003).
 1
itype_conv To specify the type of convection parameterization
  1. Tiedtke scheme
  2. Kain-Fritsch scheme (Caution: Not fully tested yet)
  3. Bechtold scheme (Caution: Not yet in the official code)
  4. Shallow convection based on Tiedtke scheme
 0
ltiedtke
lkainfri
lbechtol
lshallow		 These variables have been eliminated. They are replaced by itype_conv -
/DIACTL/ itype_diag_t2m To specify the method for computing the 2m temperature:
  1. Computation with an exponential canopy profile, but with a diagnostic Prandtl layer interpolation even for scalars, using an adopted canopy layer resistance.
  2. Computation with exponential canopy profile.
 1
itype_diag_t2m To specify the method for computing the maximal wind gusts:
  1. Dynamical gust derived from lowest model layer.
  2. Dynamical gust derived from 30 m.
  3. Dynamical gust derived after Brasseur.
1
/NUDGING/ itype_obfile to determine, from which file(s) the observations are read
  1. read observations from AOF
  2. read observations from NetCDF files
 1
ycdfdir directory in which the NetCDF input observation files reside ./

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8. Changes of Results

Because of the many changes, the results of all applications have been changed. New reference data sets are now provided on the ftp-server for both dynamical cores, the Leapfrog-scheme (coarser resolution with 7 km) and the Runge-Kutta scheme (finer resolution with 2.8 km).

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