Spatial and Temporal Variability in Midlatitude Cold Pools from C3LOUD-Ex Observations

In the midlatitudes, cold pools (regions of dense air created by evaporation and melting of precipitation) are known to influence important aspects of convective storms such as convective initiation, squall line maintenance and severity, and likelihood of tornadogenesis in supercells. Cold pools are turbulent by nature and therefore should exhibit rich spatial structure, but high spatiotemporal resolution observations are largely lacking. Such observations are critical to further our understanding of cold pool processes and their impacts on convection and to evaluate and improve their representation in models. Several outstanding observational questions about midlatitude cold pools remain, such as: What is the variability of temperature, moisture, pressure, and winds in different portions of the cold pools? How variable are cold pool depths? One goal of the CSU Convective CLoud Outflows and UpDrafts Experiment (C³LOUD-Ex) was to obtain high spatial and temporal resolution observations of cold pools in order to address these questions.

C³LOUD-Ex was conducted in northeastern Colorado, southeastern Wyoming, and southwestern Nebraska from 11-20 July 2016 and 1 May – 9 June 2017. To measure horizontal and vertical variability in cold pools, several instrument platforms were utilized, including pairs of radiosonde launches separated horizontally by 1 km and co-located with a fleet of 6 small Unmanned Aerial Systems (sUAS) and 3 surface weather stations. The CSU-CHILL research radar was also employed to obtain sector scans and range height information about the observed cold pools. In this study, analyses of cold pool variability will be presented, including variability on horizontal scales of 100 m to 1 km from the in-situ observation suite; vertical variability and cold pool depths from radiosondes, sUAS observations, and CHILL range height scans; and temporal variability from sUAS, surface stations, and CHILL data. Preliminary results suggest there is significant variability in cold pool properties on horizontal scales of less than 1 km, highlighting the need for sub-kilometer model grid spacings. Observed cold pool depths range from a few hundred meters to over 2 km, and the vertical structure of cold pools resembles high-resolution idealized model simulations, suggesting that such simulations can be used to help interpret the cold pool observations.