Imaging boundary layer roll signatures for climate applications

The planetary boundary layer (PBL) mean flow frequently consists of an organized secondary circulation in the form of counter rotating rolls embedded in the mean flow. Theory predicts this is the case in unstable, neutral and slightly stable stratification and for a range of baroclinic conditions. Although generally associated with the formation of “cloud streets”, numerical and theoretical studies suggest that rolls should be present whenever there is sufficient shear to organize the convection, including cloud free conditions. Anecdotal observations from case studies support these numerical and theoretical expectations. However, there exist no studies that can establish the extent and statistical frequency of roll occurrence. The sampling frequency and coverage of satellite data make them an invaluable, and often the only, source of observations on global and regional scales. Among the different types of satellite borne remote sensors the SAR is singular in its ability to detect and quantify the PBL roll signature on the ocean surface. The authors discuss and test the ability of the RADARSAT synthetic aperture radar (SAR) observations to establish boundary layer roll climatology and frequency statistics