Variability Within and Among Midlatitude Cold Pools

Cold pools generated by evaporation and melting from deep convective clouds play many important roles in weather, climate, and society. However, much is still to be learned about variability in cold pool properties. For example, for a given environment, what range in temperature and wind perturbations can be achieved? How variable are water vapor perturbations in cold pools over land? What are the scales of variability in a single cold pool? Answers to these questions have important implications for cold pool feedbacks to convection, their societal impacts such as aviation hazards or emission of aerosol (e.g. “thunderstorm asthma”), and for the development of cold pool parameterizations in global climate models.

The goal of this work is to investigate the variability in cold pool properties within a single cold pool and among different cold pools in a similar environment. To this end, we utilize observations collected during several recent field campaigns in the High Plains of the U.S. during late spring, including the CSU Convective CLoud Outflows and UpDrafts Experiment (C³LOUD-Ex) in 2016-2017 and the BioAerosols and Convective Storms (BACS) field project in 2022-2023. During both C³LOUD-Ex and BACS, observations of variability in the vertical (and horizontal for C³LOUD-Ex) directions were collected in pre- and post-cold pool conditions using radiosondes, surface stations, and drones. Finally, the Field Experiment on Submesoscale Spatio-Temporal Variability in Lindenberg (FESSTVaL), conducted in eastern Germany during summer 2021, consisted of a dense network of 99 surface stations and measured variability in near-surface cold pool properties on scales of 100 m to 15 km.

Variability in cold pool properties throughout the cold pool depth are examined using the C³LOUD-Ex and BACS radiosonde datasets and drone observations. The results show distinctly different vertical cold pool structure, depending on the type of convection that produced the cold pool. Additionally, the sign, magnitude, and vertical structure of the water vapor in the cold pools are highly variable and depend on the cold pool’s depth and the pre-cold pool boundary layer structure. Finally, scales of variability in single cold pools are examined using the FESSTVaL network and augmented by C³LOUD-Ex observations. The results indicate that cold pool temperature variability is enhanced on scales larger than one km but suppressed on sub-km scales on average, as compared to pre-cold pool conditions, although the results are highly dependent on the stage in the cold pool lifecycle. Mechanisms explaining this variability are assessed using idealized and case study numerical simulations of cold pool events. These will be presented along with implications for representing cold pools in numerical models and their wide-ranging impacts.