Characterizing Cold Pool Interactions Over Land with Observational Data from the Netherlands

Abstract:

When precipitation evaporates in a sub-saturated boundary layer, it cools the air and produces dense downdrafts, which flow towards the surface and can spread horizontally as a gust front. These spreading “cold pools” (CPs) can trigger convection and thus new precipitation events due to dynamical and thermodynamical lifting mechanisms. Due to their role in the local organization of convection, CP properties are currently being studied with the use of high-resolution numerical simulations. Measurement campaigns have been conducted over the ocean to validate the models. However, fewer studies have specifically targeted cold pools over land.

We use the observational network of the Netherlands (specifically the 213m Cabauw boundary layer measurement tower and the Herwijnen polarimetric radar) to study CPs developing from summer convection and their role in triggering new convective events over land. We create an algorithm that detects the passage of a CP from the Cabauw tower time series to automatize the finding of CPs from a point measurement. The detected CP gust fronts and their generating precipitation cells are studied with imagery from the Herwijnen radar, situated in proximity to the Cabauw tower. We explore the characteristics of the CP gust fronts and interiors with the Cabauw tower time series, and look for evidence of vortex rings, accumulated moisture in the leading edge and dry CP interiors. Gathering all the CP cases found, we show the measured CP properties in dependence of the precipitation intensity and of the environmental conditions. We find positive correlations between the temperature drops and the wind gusts associated with the CPs, and explore the correlations between these properties, the precipitation intensity of the generating cell, and the mean atmospheric moisture before the event. These links will help gain more insight into the role of CPs in organizing convection over land.