Cloud Organization and Precipitation within Mesoscale Disturbances

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The purpose of this project is to investigate the cloud organization and precipitation processes within the mesoscale disturbances. The research was initiated to study in a numerical models. In a three dimensional model, intense shallow cloud bands developed along low level temperature step. When parabolic winds with low level beering blow across this low level temperature step, large cloud cells appear within the cloud band. Precipitation is greatly enhanced.King Air observation in Hawaii not only confirmed the model results but also revealed the formation of stable-air at the upwind side which is important to trigger the new cloud band. Transport of low level air into the cloud band induced the gentle dowdraft in a wide area at the upwind side of cloud band.Precipitation mechanisms were studied in three dimensional cloud models with detailed microphysics.With ice, it precipitates earlier, heavier and lasts longer. In a maritime clouds, frozen drops play an important role of the enhancement of precipitation according to the model results.To confirm the model results, newly developed radiosondes were ascent into the equatorial cumulonimbus. Many ice crystals as well as frozen particles-hail were observed. Analysis showed that a unique rainwater accumulation process is held just above the freezing level. Raindrops freeze above O*C and continue to grow because frozen particles do not break as do raindrops.Aircraft observation in Hokuriku winter cumuli revealed new secondary ice multiplication by the collision between large and small graupel.