Lightning Activity and Precipitation Characteristics of Typhoon Molave (2009) Around Its Landfall

Cloud-to-ground (CG) lightning data, storm intensity and track data, and the data from a Doppler radar and the Tropical Rainfall Measuring Mission (TRMM) satellite, are used to analyze the temporal and spatial characteristics of lightning activity in Typhoon Molave (0906) during different periods of its landfall (pre-landfall, landfall, and post-landfall). Parameters retrieved from the radar and the satellite are used to compare precipitation structures of the inner and outer rainbands of the typhoon, and to investigate possible causes of the different lightning characteristics. The results indicate that lightning activity was stronger in the outer rainbands than in the eyewall and inner rainbands. Lightning mainly occurred to the left (rather than "right" as in previous studies of US cases) of the moving typhoon, indicating a significant spatial asymmetry. The maximum lightning frequency in the tropical cyclone (TC) eyewall region was ahead of that in the whole TC region, and the outbreaks of eyewall lightning might indicate deepening of the cyclone. Stronger lightning in the outer rainbands is found to be associated with stronger updraft, higher concentrations of rain droplets and large ice particles at elevated mixed-phase levels, and the higher and broader convective clouds in the outer rainbands. Due to the contribution of large cloud nuclei, lightning intensity in the outer rainbands has a strong positive correlation with radar reflectivity.The ratio of positive CG lightning in the outer rainbands reached its maximum 1 h prior to occurrence of the maximum typhoon intensity at 2000 Beijing Time (BT) 18 July 2009. During the pre-landfall period (0300 BT 18 July-0050 BT 19 July), the typhoon gradually weakened, but strong lightning still appeared. After the typhoon made landfall at 0050 BT 19 July, CG lightning density rapidly decreased, but the ratio of positive lightning increased. Notably, after the landfall of the outer rainbands at 2325 BT 18 July (approximately 1.5 h prior to the landfall of the TC), significantly higher ice particle density derived from the TRMM data was observed in the outer rainbands, which, together with strengthened convection resulted from the local surface roughness effect, might have caused the enhanced lightning in the outer rainbands around the landfall of Molave.