Cloud Organization and Precipitation within Mesoscale Disturbances

本项目的目的是研究中尺度扰动中的云组织和降水过程。这项研究是在数值模型中开始研究的。在三维模式中，强的浅层云带沿低层温度阶梯发展。当带有低层蜂鸣的抛物线风吹过这个低层温度台阶时，云带内会出现大的云团。在夏威夷进行的King Air观测不仅证实了模式的结果，而且发现在迎风侧形成了稳定的空气，这对触发新的云带具有重要意义。低层空气进入云带，在云带上风侧引起大范围的平缓下沉气流，利用三维云模式和详细的微物理模型研究了云带的降水机制，发现有冰的情况下，降水早、重、持续时间长。结果表明，在海洋云中，冻结的水滴对降水的增强起着重要的作用。为了验证模型的结果，新研制的无线电探空仪上升到赤道积雨云中。观测到了大量的冰晶和冻结的冰雹颗粒。分析表明，一个独特的雨水积累过程保持在略高于冰点的水平。雨滴在O*C以上冻结，并继续增长，因为冻结的粒子不会像雨滴那样破裂。北国冬季积云中的飞机观测发现，由于大小砾石的碰撞，新的次生冰繁殖。

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.