A180-0003
A stochastic shallow convection scheme for ICON - two flavors.
A stochastic shallow convection scheme for ICON - two flavors.
Tuesday, 15 December 2020
Poster
Abstract:
The Icosahedral Model (ICON) of the German Weather Service (Deutscher Wetterdienst, DWD) is used for numerical weather predicition at global and regional scales. In the regional mode, resolutions range roughly from 10km down to 1km horizontal grid spacing. Deep convective transport is partially resolved at these scales, but shallow convection remains poorly represented without a parameterization.
A stochastic shallow convection scheme was developed in collaboration with the Max Planck Institute for Meteorology, and is now being implemented in ICON with a view towards operational use. The scheme is scale-adaptive and renders resolution-dependent tuning of the convection parameterization unnecessary. Mass flux limiters essential for the stable operation of the unaltered convection scheme can be removed when the stochastic perturbations are introduced.
Alongside the original, explicit stochastic scheme an approximation using stochastic differential equations (SDE) has been developed. The advantage of the SDE version is a lower computational and memory cost, and the ability to save and restart the model‘s stochastic cloud state easily. Running the two versions of the stochastic scheme in piggy-backing mode (i.e. running one version of the scheme interactively, the other passively) we can demonstrate equivalency of the two approaches.
We present results from test cases covering shallow and deep convective days over Germany, as well as oceanic shallow convection over the Atlantic during the EUREC4a field campaign. The scheme improves low cloud cover, 2m temperature and humidity biases relative to SYNOP observations, and improves upwelling shortwave radiation at the top of the atmosphere for the oceanic trade cumulus regime.
A stochastic shallow convection scheme was developed in collaboration with the Max Planck Institute for Meteorology, and is now being implemented in ICON with a view towards operational use. The scheme is scale-adaptive and renders resolution-dependent tuning of the convection parameterization unnecessary. Mass flux limiters essential for the stable operation of the unaltered convection scheme can be removed when the stochastic perturbations are introduced.
Alongside the original, explicit stochastic scheme an approximation using stochastic differential equations (SDE) has been developed. The advantage of the SDE version is a lower computational and memory cost, and the ability to save and restart the model‘s stochastic cloud state easily. Running the two versions of the stochastic scheme in piggy-backing mode (i.e. running one version of the scheme interactively, the other passively) we can demonstrate equivalency of the two approaches.
We present results from test cases covering shallow and deep convective days over Germany, as well as oceanic shallow convection over the Atlantic during the EUREC4a field campaign. The scheme improves low cloud cover, 2m temperature and humidity biases relative to SYNOP observations, and improves upwelling shortwave radiation at the top of the atmosphere for the oceanic trade cumulus regime.