资源环境科技发展态势分析平台

Drizzle is frequently observed in marine stratocumulus clouds and plays a crucial role in cloud lifetime and the radiation budget. Most drizzling stratocumulus clouds form drizzle virga below cloud base, where subcloud scavenging and evaporative cooling are important. We use unique ground-based cloud radar observations (1) to examine the statistical properties of drizzle frequency and virga depth and (2) to test a simple analytical relationship derived between drizzle virga thickness (Hv) and cloud thickness (Hc). Observations show that 83% of marine stratocumulus clouds are drizzling although only 31% generate surface precipitation. The analytical expression for Hv is derived as a function of Hc and subcloud relative humidity considering in-cloud accretion and subcloud evaporation of drizzle drops. The derived third-order power law relationship, H-v similar to H-3(c), shows good agreement with long-term observational data. Our formula provides a simple parameterization for drizzle virga of stratocumulus clouds suitable for use in models.

Plain Language Summary Drizzle plays a crucial role in cloud lifetime and radiation properties of marine stratocumulus clouds. Understanding where drizzle exists in the subcloud layer, which depends on drizzle virga depth, can help us better understand where below-cloud scavenging and evaporative cooling and moisturizing occur. Here we examine the statistical properties of drizzle frequency and virga depth of marine stratocumulus based on unique ground-based remote sensing data. Results show that marine stratocumulus clouds are drizzling nearly all the time. In addition, we derive a simple scaling analysis between drizzle virga thickness and cloud thickness. Our analytical expression agrees with the observational data reasonably well, which suggests that our formula provides a simple parameterization for drizzle virga of stratocumulus clouds suitable for use in other models.