Characteristics of low-cloud variability over the Azores

Description

Marine boundary-layer (MBL) clouds over the northeast Atlantic exhibit substantial differences compared to MBL cloud systems over the eastern subtropical Pacific basins. The ARM Mobile Facility (AMF) was deployed for a year and a half on Graciosa Island in the Azores in order to sample MBL and cloud system properties. In contrast with the other stratocumulus regimes, the northeast Atlantic is frequently influenced by intrusions of synoptic systems, even during the summer months. Data from the AMF deployment indicate a wide variety of MBL thermodynamic and cloud system configurations that at times differ greatly from the classical model of the stratocumulus-topped boundary layer. We focus on joint distributions of liquid water path, CCN concentration, large-scale vertical motion, and stability in order to establish the range of the parameter space that the cloud systems inhabit. These observational analyses serve as a guide to constrain initial numerical model sensitivity experiments to establish the most important factors governing cloud-system variability over the northeast Atlantic.