Detection and Characterization of Cold Pools over Germany in the DYAMOND Simulations

Cold pool generated by convective clouds is an evaporatively cooled dry region which spreads out near the surface. Studying the cold pool characteristics enhances our understanding about convective clouds such as shallow-to-deep transition of convective clouds, long-lived squall line, and triggering secondary convection. In this study, cold pools over Germany are detected and characterized using phase 0 results of DYAMOND (stands for DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains) intercomparison project. We aim to understand how the cold pool characteristics over Germany depend on topographic height, accompanying cloud size, and model.

Nine model results of the DYAMOND collection are remapped into 0.1˚ × 0.1˚ regular grid system. Cold pool cluster is defined as a cluster with an area larger than ~64 km² (4 grids), with the perturbation virtual (density) potential temperature below 2 K and the maximum precipitation rate greater than 1 mm h^–1. Detected cold pools are re-categorized by the topographic height to decompose cold pools related to orographic precipitation and by the accompanying cloud size to decompose cold pools related to large cloud system.

During simulated period (40 days from 1 August 2016), model averaged total detected cold pool number is 5.59 h^–1. Although more number of cold pool clusters are detected over low topographic area (1.34 h^–1 and 4.25 h^–1 over high and low area, respectively), area weighted cold pool cluster number is 3.82 times larger over high topographic area (17.55 h^–1 and 4.60 h^–1 over high and low area, respectively). Most of cold pool clusters are accompanied by larger clouds than themselves (78 %) and 9 % of cold pools are detected outside of cloud cover. Except for the cold pools accompanied by clouds of synoptic low pressure system, most of cold pools are detected in the daytime. Cold pool clusters over high topographic area are larger, more non-circular shaped, colder, and with lower wind speed than those over low topographic area. Cold pool clusters accompanied by small clouds are colder, drier, with higher wind speed, and with stronger precipitation than those accompanied by large clouds. In this study, relationship between cold pool characteristic parameters in each category is also investigated. To understand how cold pool feature varies from model to model, the cold pool characteristic parameters in each DYAMOND model result are compared and analyzed.