X-Band Dual-Polarization Radar Observations of Precipitation Core Development and Structure in a Multi-Cellular Storm over Zoshigaya, Japan, on August 5, 2008

摘要

A multi-cellular storm over the Zoshigaya area of Tokyo, Japan (5 August 2008) was observed by two X-band dual-polarization radars, and this paper aims to investigate the structure of the precipitation cores within its individual precipitation cells. The precipitation cell and core are defined here on the basis of liquid water content (LWC).The storm comprised 20 precipitation cells, each with a precipitation core. Of these, 17 cells were characterized by a single precipitation core (single-core cells) and lasted for less than 30 minutes (5-25 minutes). In contrast, the other three cells consisted of several auxiliary precipitation cores (multi-core cells) that were produced in succession and descended to the ground each lasting approximately 15 minutes, the cells themselves were relatively long-lived (≥40 minutes). Single-core cells developed via updrafts driven by low-level convergence that persisted for approximately 10 minutes before being converted to a downdraft by precipitation loading. Without the supporting updraft, the precipitation core fell to the ground 5-25 minutes after its first appearance. In contrast, replacement of precipitation cores in multi-core cells during their mature stage was driven by periodic strong updrafts associated with a low-level southeasterly inflow that supplied warm, moist air to the precipitation cell.The results of a statistical analysis of precipitation cell and core are presented. The rainfall amount from each precipitation cell was proportional to the cell’s lifetime, with a slope of 0.89 for the relationship and a correlation coefficient of 0.95. The average updraft and downdraft velocities of multi-core cells (7.9 and 4.7 m s-1, respectively) were stronger than in the single-core cells (5.2 and 3.7 m s-1, respectively). The average liquid water content of precipitation cores in single-core cells was 4.0 g m-3, whereas the multi-core cells averaged 5.3 g m-3. The average formation heights of single- and multi-core cells were 4.7 km and 4.6 km, respectively. The intensity and formation height of the precipitation cores are approximately proportional to each other.