Multiscale impacts of precipitation on a boundary layer cloud fraction transition

Abstract:

Observational and modeling studies indicate that the precipitation process may play an important role in cloud fraction changes across the transition from stratocumulus to shallow cumulus clouds in boundary layer cloud regimes. A synthesis of satellite measurements is used to examine the impacts of light precipitation on boundary layer cloud fraction transition in the southeast Pacific at multiple scales, from the large-scale climatology to seasonal, diurnal, and at mesoscales. Results show a local conditional precipitation intensity maxima in the region of the largest climatological cloud fraction gradient. These precipitation intensity peaks migrate with the seasonal and diurnal movement of the large-scale cloud fraction gradient. At mesoscales, cloud fraction in areas surrounding precipitation decreases more rapidly than around non-precipitating clouds, particularly in the stratocumulus to shallow cumulus transition region. Cloud fraction in areas of predominantly stratocumulus shows little sensitivity to the presence of precipitation, while cloud fraction in areas dominated by shallow cumulus actually increases when precipitation is present. The changes in cloud fraction seem relatively insensitive to rain frequency, but sensitive to precipitation intensity, rain cell size, and cloud liquid water path, with higher precipitation rates, larger raining cells, or lower cloud liquid water path showing larger negative mesoscale cloud fraction anomalies. Further analysis on role of precipitating cell organization and spacing is planned.