Simulation of the evolution of the charge structure during the landfall of Typhoon Molave (2009)

The charge structure and formation in Typhoon Molave (2009) before and after its landfall and during its decaying stage are investigated using satellite observations and lightning detection data as well as a mesoscale simulation. Results show that Molave was intensifying prior to landfall with a well-defined eye and relatively high-frequency lightning activities in the eyewall. Convections near the eyewall exhibited a positive tripole charge structure with a negative charge region located between the levels of -25℃ and -10℃ sandwiched by two positive charge regions. However, the charge structure of the convections became a negative bipole with a negative charge in the middle and a positive charge at the bottom of the convective clouds after Molave reached its maximum intensity. The charge structure in the eyewall convections is closely associated with the typhoon intensity, but not directly correlated with the landfall process. The outer spiral rainbands displayed a positive tripole charge or a positive bipole charge in different stages of Molave. Previous studies suggested that the outer rainbands of a typhoon only feature a positive bipole charge structure. The positive tripole charge structure in Molave formed with different mechanisms:One mechanism resembled that in the eyewall, and the other mechanism was related to a positive charge region composed of hails and a positive bipole region composed of graupels and ice crystals in the upper level, which formed a positive tripole charge structure. During the decaying stage of Molave, weak convections were mainly featured by a negative bipole similar to that in the terrestrial thunderstorms in dissipative stage. In addition, different charge structures and corresponding convection intensity are also discussed in this paper.