A Climatology of Cold Pools at the ARM Eastern North Atlantic Site

We develop a method to identify cold pools at the ARM Eastern North Atlantic (ENA) site on Graciosa Island and examine the statistics of precipitation-driven cold pools from 2016-2023. At the ENA site, cold pools tend to be generated by the evaporation of light rain within the marine boundary layer (MBL) and are often similar in magnitude to other types of thermodynamic variability. Traditional methods that use fixed thresholds to detect abrupt drops in surface temperature can mistakenly attribute natural diurnal and annual cycles of solar-driven variability to cold pools if time-varying background conditions are not accounted for. To address this, our approach leverages deviations greater than the time-varying background levels in the time series of near-surface temperature data from meteorological stations. This method does not rely on fixed location-specific thresholds, making it suitable for any site with a long observational record. By comparing the empirical distributions of "background" conditions to "cold pool candidate" times, our retrieval strategy assigns confidence weights to potential cold pool events, improving detection accuracy.

We validate our approach with zenith-pointing Doppler lidar and scanning radar during the ACE-ENA field campaign. Additionally, we explore relationships between cold pool activity, observed aerosol concentrations, and weather regimes. Often, gauge-detected rain events are not associated with cold pools due to factors such as decoupled and/or humid MBLs. Our retrieval skillfully identifies cold pools that are not associated with co-located rain, which can occur when active rain passes nearby, when rain has ceased just before reaching the station, or when rain evaporates as virga above the site. Elucidating distinct cold pools at ENA will lead to a greater understanding of the dynamics and aerosol budget of the MBL and how they feed back to mesoscale cloud morphological structures.