Understanding clouds and precipitation in complex terrain: the Convective and Orographically Induced Precipitation Study (COPS)
Author
Volker G. Wulfmeyer — Hohenheim University
Category
Field Campaigns
Description
Synergetic observation of convection initiation in the COPS domain. Overlaid are a three-channel composite of the MSG satellite and a radar composite as well as mixing ratio and wind fields from a densified surface station network. These results are used to study the interaction between thermally induced flows in the region and convection initiation. Here, the development of a convergence line over the southern crest of the Black Forest was caused by flow splitting of south-westerly flow and slope and valley flows from the western side of the Black Forest.
For weather forecasts and climate simulations, correct modeling of clouds and precipitation is crucial. Particularly over the land surface in complex terrain, excellent performance is required for many applications such as protection of crops, flash flood forecasting, and land-use management in the future.
However, from nowcasting to medium-range weather forecasting to decadal climate simulations, the performance of models does by far not meet the needs of end users and decision makers. For instance, with respect to precipitation, weather forecasts suffer from high false-alarm ratios and low probabilities of detection. Both weather and climate simulations show substantial systematic errors, such as windward-lee effects and large phase errors in the diurnal cycle.
The World Weather Research Programme (WWRP) Research and Development Project (RDP) Convective and Orographically Induced Precipitation Study (COPS) was designed and performed to understand and to remove these errors by combination of extensive observational and modeling efforts. COPS was strongly supported by ARM, e.g., the operation of the ARM Mobile Facility for nine months in the center of the COPS region in southwestern Germany/eastern France.
We present highlights of the COPS research along the chain of processes leading to precipitation. These include observations of
- land-surface exchange processes in dependence of land-use and soil moisture,
- thermally induced slope flows in complex terrain leading to a modulation of moisture, CAPE, and CIN across convergence lines,
- initiation of convection and clouds, and
- aerosol-cloud-precipitation microphysics.
These observations are accompanied by various data assimilation and ensemble modeling studies on the convection-permitting scale. The following main conclusions can be derived from these results: Extreme care has to be taken in the description of land-surface properties and processes, but still the relationship between latent and sensible heat fluxes on soil moisture is not resembled by models. Convection-permitting simulations remove several systematic errors caused by the parameterization of deep convection so that this resolution should be aimed for the next generation of weather and climate simulations. Advanced data assimilation systems in combination with new observations from surface networks and satellites have a huge potential to approach further the limits of predictability of key processes in the Earth system such as precipitation.
