Occurrence of aerosol regimes and sustained low cloudiness over the eastern north Atlantic as a function of synoptic regime

Description

The 20-month CAP–MBL deployment of the ARM Mobile Facility (AMF) over eastern north Atlantic (ENA) region in the vicinity of the Azores sampled a rich array of meteorological and cloud variability. We have quantified variability in synoptic and cloud properties over the ENA using the clustering approach of self-organizing maps (SOMs), particularly focusing on the annual cycle and variability at synoptic timescales. Even in June, synoptic systems regularly influence the Azores region, and ridge-like conditions supportive of stratocumulus occur in January (~25% of the time), confirming the result from the CAP–MBL AMF deployment that low clouds are prevalent year-round. We extend this analysis to evaluate how aerosol properties (e.g., aerosol optical depth, surface CCN measurements) depend on the synoptic regime. The clustering analysis is used to classify long periods of sustained low-altitude cloudiness observed by the W-band ARM Cloud Radar (WACR) during CAP–MBL and identified by Luke and Kollias (2013). Preliminary analysis indicates that most of these cases are associated with the SOM ridge and post-trough regimes, no matter the season. These analyses are used to provide insight into suitable cases for LES modeling.