Regimes of boundary-layer structure in the Azores using data from the ARM Mobile Facility

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Description

Boundary-layer cumulus and stratocumulus clouds cool the ocean or land surface by reflecting a significant fraction of incoming solar radiation back to space while simultaneously emitting longwave radiation comparable in magnitude to that which would have been emitted by the surface if no cloud cover was present. Cloud coverage and cloud vertical structure are intimately connected to the thermodynamic and the dynamical structure of the boundary layer, but there are relatively few observations of these connections. A unique opportunity to study these connections was presented by the deployment of the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF1) on the island of Graciosa in the Azores. The present study utilizes data from the soundings launched from June 2009 until December 2010 to characterize the boundary-layer thermodynamic structure in the region, and coincident data from cloud sensing instruments including the W-band ARM cloud radar (WACR), microwave radiometer, and ceilometer are used to describe the accompanying cloud structure. Low level clouds are identified by the AMF1 cloud sensors, which are also used to exclude deep convective clouds observed during the frontal passages. Diurnal variations of the BL structure are investigated along with the relationships that exist between the observed cloud structure and the Convective Available Potential Energy (CAPE), BL inversion, liquid water path, and large-scale subsidence.