Observed relationship between drop size distribution and environmental properties in eastern Japan

Abstract. The drop size distribution (DSD) is an important property for characterising precipitation processes that sometimes lead to more intense rainfall in different climate regions. Previous studies have shown that a stationary distribution with a breakup signature can be obtained not only with ground-based disdrometers but also with remote sensing instruments such as vertically pointing radars and/or wind profilers. However, these observations do not explain how the underlying microphysical processes within convective clouds that generate more rain occur and how the environmental conditions affect these processes. This study aims to investigate the environmental conditions for the development of convective clouds that induced more intense rainfall in eastern Japan. In situ observations and operational C-band polarimetric weather radar data are used to extract the convective clouds by applying a cell-tracking algorithm, and upper-air sounding data are used to diagnose their environmental conditions. The larger diameter of the DSD is likely to be associated with higher instability, whilst the higher number concentration is likely to be archived with the higher precipitable water under the weaker vertical shear condition. Convective clouds that generate more rain should have a similar three-dimensional structure within them when the DSD has a breakup signature at ground level under a humid environment. These characteristics can be diagnosed as the microphysical processes of converting from cloud drops to raindrops and/or coalescing cloud drops and raindrops.