Turbulence Estimates in Marine Stratocumulus Clouds from Doppler Cloud Radar

The vertically pointing W-band radar in the 2008 VOCALS campaign observed 19 days of nearly homogenous marine stratocumulus clouds in the tropical southeastern Pacific.  Retrieved turbulent Doppler velocities near cloud top are compared with simulated radiative fluxes from a rapid radiative transfer model (RRTM). 

We approach studying turbulence throughout the cloud layer via simplified turbulent kinetic energy (TKE) and heat budget equations.  Results show that while there is intermittency in the turbulent buoyancy flux divergence below cloud top, positive buoyancy flux divergence is approximately balanced by heat flux resulting from radiative cooling.  At cloud top an imbalance occurs that may be due to entrainment of warm, dry inversion air.  Furthermore, this study examines the temporal evolution of turbulence in the cloud layer as a response to external forcings. The diurnal cycle of turbulence dissipation in the cloud layer reveals an increase in turbulence during the night hours.  Turbulence decreases during the day and decoupling is found around 500m below cloud top, followed by a rapid recoupling and turbulent mixing in the late afternoon.  These results are a step toward quantifying the effects of radiation on turbulence and understanding the evolution of these radiatively important marine stratocumulus clouds.