Enhanced lightning activity during merging of Super Typhoon Hinnamnor (2022) with its Southern Tropical Depression

We examined the lightning activity during the merging of two tropical cyclones (TCs), super typhoon Hinnamnor (2022) with a tropical depression (TD) to its south. To accurately characterize the lightning activity throughout the evolution of two TCs, we proposed a boundary extraction method for convective systems based on the Black Body Temperature (TBB) observations from Himawari-8. The overall lightning activity can be divided into three distinct periods. During period-2 (during the merging), the total lightning (intro-cloud, IC plus cloud-to-ground, CG flashes) of the two both increased explosively in number compared with period-1 (prior to the merging), but the proportion of CG flashes significantly decreased (to an average level of 30%) in both TCs. Interestingly, during Period-3 (after the merging), the total lightning increased again and this proportion in Hinnamnor increased rapidly and stabilized to a level close to the average of period-1 (around 50%). In addition, Hinnamnor underwent totally 6 eyewall lightning outbreaks during period-2 and period-3, the first two in period-2 occurred 4 and 6 hours before the merging. Our analysis shows that when the distance between the centers of two TCs are close enough (e.g., 500 km in this case), binary cyclone interaction may affect their convection developments, further leading to the changes in their charge structures, resulting in the lightning activity characteristics mentioned above. Additional observations involving the lightning activity during the interaction of two or multiple TCs and further numerical simulations are desired to obtain more insights into the effects of the interaction on the development of their charge structures.