Rainfall Reinforcement Associated With Landfalling Tropical Cyclones

Abstract

Landfalling tropical cyclones (TCs) often bring about heavy rainfall, which typically decreases with the weakening of the TCs. However, some TCs may suddenly be reinvigorated after they became remnants over land. Such TCs may produce even stronger rains than those during the time of their landfall. This reinvigorating phenomenon is known as Rainfall Reinforcement associated with Landfalling Tropical Cyclones (RRLTC). The TCs triggering rainfall reinforcement account for 9.7% of the total number of TCs that make landfall on mainland China, and often cause problems and surprises for forecasters. The TCs with rainfall reinforcement mostly make landfall in the area of south-east coast of China, and move primarily along two tracks, spreading northward and westward. RRLTC often occurs in the remnant of a tropical depression, which has already been downgraded from typhoon intensity, in particular in a period when the remnant has slowed down or even stagnated. The high frequency of RRLTC occurrence is in the third day after landfall and is in the northeast quadrant of a TC moving northward and in the southwest quadrants of a TC moving westward, respectively. Diagnostic analysis shows that the RRLTC usually take two kinds of tracks after they made landfall, namely, northward track and westward track. The study also shows that the RRLTC with a northward track is mainly attributed to the interaction between westerly troughs and tropical cyclone. This is the way for remnant to gain the baroclinic energy from the mid-latitude trough. Such an interaction is not appeared for northward track TCs without rainfall reinforcement.2 Rainfall reinforcement for the TCs with a westward track is mainly due to the interaction between monsoon surge cloud clusters and tropical cyclone. It’s favorable to TCs gain moisture and latent heat. Analyses show that the westward TCs would not have rainfall reinforcement if without such an interaction.RRLTC requires new energy transporting into TCs. The results of the present study indicate that baroclinic potential energy and latent heat are the two major energy sources that will trigger the remnant revival and rainfall reinforcement. On the other hand, apart from the two kinds of energy acquired by RRLTC, the land surface topography is also played the important role to increase the rainfall of TCs.