Deep Orographic Storms over the Sierra Nevada. Part II: The Precipitation Processes. Marwitz, John D..
Journal of the Atmospheric Sciences:
The thermodynamic and kinematic structure of two stable orographic storms were described in Part I based on instrumented aircraft data and single Doppler radar data. The precipitation processes in these storms are described in this paper. The storms were deep with cloud top temperatures of about -25 degrees celcius. Below the melting level the cloud droplet poplulation was continental with a mean droplet diamter < 10micrometers. Above the melting level the cloud droplet population was maritime with mean droplet diameters of 20 to 30 micrometers. Near the -5 degrees celsius level a peak in ice crystal concentration of 30 to 200 L^-1 was observed. Since most of the ice crystals were needles, a rime-splintering secondary ice crystal producation process as generally described by Hallett and Mossop was probably occuring. Calculations of the condesnation supply rates were compared with the depletion rates by deposition and accretion. The depletion rates by deposition were less than half the condensation supply rates, and the liquid water contents remained very low. Accretion is deduced to be the dominant process, which acts to deplete the condensate to near zero. Deep, stabel orographic storms over the Sierra barier, therefore, develop an efficient glaciation process.