Authors

Abstract

Marine stratocumulus clouds are intimately coupled to the turbulence in the boundary layer and drizzle is known to be ubiquitous within them. Six years of data collected at the AtmosphericRadiation Measurement (ARM)s Eastern North Atlantic (ENA) site are utilized to characterizeturbulence in the marine boundary layer and air motions below stratocumulus clouds. Profiles ofvariance of vertical velocity during clear-sky convective conditions binned by wind direction30 yielded that measurements are affected by the island when the wind direction (wdir) is between 90 and 310. Data collected during the marine conditions (wdir<90 or wdir>310) showed that the variance of vertical velocity was higher during the winter months than during the summer monthsdue to higher cloudiness, wind speeds, and surface fluxes. The variance of vertical velocity duringmarine conditions and cloud fraction also exhibited a distinct diurnal cycle with higher values during the nighttime than during the daytime. Detailed analysis of 32 cases of drizzling marine stratocumulus clouds showed that for a similar amount of radiative cooling at the cloud top the 1) drizzle increasingly falls within downdrafts with increasing rain rates, 2) the strength of the downdrafts increases with increasing rain rates, and 3) the correlation between vertical air motion and rain rate is highest in the middle of the sub-cloud layer. The results presented herein haveimplications for climatological and model evaluation studies conducted at the ENA site, along with efforts of accurately representing drizzle-turbulence interactions in a range of atmospheric models.