Identifying Meteorological Controls on Open and Closed Mesoscale Cellular Convection Associated with Marine Cold Air Outbreaks

Abstract

Mesoscale cellular convective (MCC) clouds occur in large-scale patterns over the ocean and have important radiative effects on the climate system. An examination of time-varying meteorological conditions associated with satellite-observed open and closed MCC is conducted to illustrate the influence of large-scale meteorological conditions on cloud development. Marine cold air outbreaks (MCAO) influence the development of open MCC and the transition from closed to open MCC. MCC neural network classifications on MODIS data for 2008 are collocated with CERES data and ERA-Interim Reanalysis to determine the radiative effects of MCC and their thermodynamic environments. Closed MCC are found to have much higher albedo on average than open MCC for the same cloud fraction. Three metrics for meteorological controls are tested for MCC predictive ability: sea-air temperature difference (∆T), estimated inversion strength (EIS), and a MCAO index (M). These metrics illustrate the importance of atmospheric surface forcing and static stability for open and closed MCC formation. Predictive sigmoidal relations are found between M and MCC frequency: strong and positive for open MCC, weaker and negative for closed MCC. The seasonal cycle of open MCC is most correlated with M, while the seasonality of closed MCC is most correlated with EIS. Open and closed MCC are, on average, best distinguished by M of all the metrics tested. The possibility of a MCC cloud feedback is discussed.