A Case Study on the Soil Temperature Cooling Mechanism by Convective Cold Pools using Observation Network Data

Convective cold pool is an air mass that is relatively colder than its surrounding air, and is mainly generated by latent cooling of precipitating hydrometeor in convective clouds. As it spreads out, it interacts with the surrounding air through entrainment and with the surface/soil through latent/sensible heat fluxes. In this study, we investigate how the surface/soil thermodynamic properties are affected by the passage of convective cold pools. To that aim, we use observational network data including atmospheric and surface/soil measurements, which were obtained from the intensive measurement campaign FESSTVaL that took place in Lindenberg, Germany in the summer of 2021. For this study, three cold pool cases are selected for analysis. All the observations show a clear decrease in air temperature as well as in surface temperature associated with the passage of the cold pools, but only some of the observations also show a decrease in soil temperature. Analysis reveals that the soil is more likely to cool when the soil is also wettened by precipitation. To understand the mechanism by which the increase in soil moisture affects the decrease in soil temperature, we conduct a simple ideal thermal diffusion model that mimics the passage of a cold pool and the propagation of the signal into the soil. The ideal model results reproduce well the observed soil temperature changes, and shows that the increase in soil moisture due to precipitation affects the heat capacity and the thermal conductivity of the soil, allowing the cold signal to propagate into the soil.