Modification of raindrop size distribution due to seeder–feeder interactions between stratiform precipitation and shallow convection observed by X‐band polarimetric radar and optical disdrometer

摘要

The seeder–feeder interactions (SFIs), where raindrops from upper clouds grow by accreting cloud droplets in the lower clouds, have been extensively studied. However, there are few studies on the modification of raindrop size distribution (DSD) through this process. In the present study, rainfall from the landfalling rainbands of a typhoon was observed using an optical disdrometer and an X‐band polarimetric radar. Rainfall was classified into the following three types based on the DSD characteristics at the surface and the existence of a ρ _(HV)minimum in the upper layer: convective rainfall accompanied by a melting layer (type SF), convective rainfall without a melting layer (type C), and stratiform rainfall with a melting layer (type S). Type SF rainfall was regarded as having undergone SFIs between stratiform precipitation and shallow convection. The DSD for SF type rainfall was characterized by more small‐ to medium‐sized raindrops and a larger normalized intercept parameter than rainfall types C and S. An analysis using vertical profiles of radar‐derived DSD parameters for type SF rainfall suggested that the median‐volume diameter of raindrops increased by accreting cloud droplets in the lower clouds, and that small‐ to medium‐sized raindrops were produced by a warm rain process and breakup of raindrops. Seeder–feeder interactions (SFIs) have been studied extensively; however, relatively few studies have examined the raindrop size distribution (DSD) associated with this process. In the present study, rainfall enhanced by SFI was observed using a disdrometer and a polarimetric radar. The DSD was characterized by a large number of small‐ to medium‐sized raindrops and a large normalized intercept parameter.