Simulation of the electrification of a tropical cyclone using the WRF-ARW model: An idealized case

Abstract

Evolution of the electrification of an idealized tropical cyclone (TC) is simulated by using the Advanced Weather Research and Forecasting (WRF-ARW) model. The model was modified by addition of explicit electrification and a new bulk discharge scheme. The characteristics of TC lightning is further examined by analyses of the electrification and the charge structure of the TC. The findings thus obtained are able to unify most of the previous inconsisitent observational and simulation studies. The results indicate that the TC eyewall generally exhibits an inverted dipole charge structure with negative charge above the positive. In the intensification stage, however, the extremely tall towers of the eyewall may exhibit a normal tripole structure with a main negative region between two regions of positive charge. The outer spiral rainband cells display a simple normal dipole structure during all the stages. It is further found that the differences in the charge structure are associated with different updrafts and particle distributions. Weak updrafts, together with a coexistence region of different particles at lower levels in the eyewall, result in charging processes that occur mainly in the positive graupel charging zone (PGCZ). In the intensification stage, the occurrence of charging processes in both positive and negative graupel charging zones is associated with strong updraft in the extremely tall towers. In addition, the coexistence region of graupel and ice crystals is mainly situated at upper levels in the outer rainband, so the charging processes mainly occur in the negative graupel charging zone (NGCZ).