Analysis of drizzle reflectivity threshold using in-situ measurements

The drizzle plays an important role in determining the cloud lifetime and evolution.Millimeter wave radar is suitable for detecting non-precipitating and weak precipitating clouds.It is of great valuement to know whether the drizzle occurs or not by the millimeter wave radar measurements.In this paper,the radar reflectivity factor of drizzle is calculated based on the dataset of cloud droplet distribution observed by aircraft.In comparison with the simultaneous radar observations,there is a good agreement between the two reflectivities.The result shows that the reflectivity factor threshold of drizzle derived from in-situ measurements can be used by the radar to diagnose the occurrence of the drizzle.The threshold of reflectivity factor to distinguish drizzle and cloud particles is derived by analyzing the probability distribution function of reflectivity factor due to cloud particles and drizzle drops.Usually,the reflectivity factor of cloud particles is below-5dBz while the value of drizzle is above-20dBz.A value between-15and-12dBz can be used as the threshold of drizzle.