Characterizing cold pool interactions over land with observational data from the Netherlands

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 (meteorological stations and radar) to study CPs developing from summer convection and their role in triggering new convective events over land. Detailed information about CP gust fronts in terms of temperature, wind speed, heat fluxes, moisture and pressure at high vertical resolution is obtained from time series, measured at the 213-meter Cabauw tower. We aim to create an algorithm that detects the passage of a CP from the tower time series to automatize the finding of CPs from a point measurement. To confirm the results, we have access to temperature time series from a spatially dense crowdsourcing weather station network (WOW-NL).

The properties of the detected CPs are further studied with imagery from the Herwijnen Doppler radar, situated in proximity to the Cabauw tower. We can see clear signatures of spreading CPs in reflectivity plots, probably caused by the upwelling of dust and insects in the gust front. We currently explore how this can serve as a direct way of visualizing the dynamics of CPs and their collisions.

With enough observations of CPs, we expect to learn more about the CP spreading velocity and lifetime in dependence of precipitation intensity of the generating precipitation cell and eventually triggered cell. This link will help gain more insight into the role of CPs in organizing convection over land.