| J.S. Gibson and A.S.Frisch NOAA Wave Propagation Laboratory Boulder, C0 80303 303-497-6148 |
D.H. Lenschow National Center for Atmospheric Research Boulder, C0 80301 303-497-8903 |
During June 1992 the NOAA Kband (8.6mm wavelength) radar participated in the ASTEX (Atlantic Stratocumulus Transition Experiment) on the island of Porto Santo, Madeira, Portugal. For about 70% of the operations, the radar measurements were made with the antenna pointing vertically to make turbulence measurements in the cloudy portion of the cloud capped marine boundary layer. By using cloud droplets as an air motion tracer, we were able to compute the variance and skewness of the vertical velocity from the Doppler measurements.
The first examined set of measurements show that most of the turbulent motion
is confined to the upper half of the stratus cloud, with negative buoyancy near
the cloud top accelerating the air downward. This process generates a well
mixed layer in the upper half of the cloud. Below this layer, the cloud is a
barrier to mixing with the underlying planetary boundary layer.