Factors Affecting the Weakening Rate of Landfalling Tropical Cyclones Over China

Based on the 6-hourly tropical cyclone best track and global reanalysis data, statistical analyses and a machine learning approach are used to identify/quantify factors that affect the relative weakening rate (RWR) of landfalling TCs (LTCs) over China mainland during 1980–2020. Results show that the enhanced RWR of LTC events usually occurs when LTCs move into regions with large environmental vertical wind shear (VWS), large surface roughness (SURR), high land surface soil temperature (SOILT), low surface latent heat flux (SLHF), and with relatively faster translational speeds (SPD). The SPD and SURR are dominant factors determining the RWR of LTCs over China mainland, contributing about 20% and 18.5% to the RWR of LTCs. VWS is also a key factor affecting RWR of LTCs with mid-level VWS contributing 17.8% to RWR of LTCs and low- and deep-level VWS contributing about 12.9% and 11.2%, respectively. Furthermore, factors affecting the LTC weakening rate in south and north China are different. In north China, the VWS at different levels are all highly correlated with LTC RWR after landfall, whereas the influence of mid-layer VWS shows significant correlation with LTC RWR in south China. In addition, surface characteristics, including SURR, SLHF, and SOILT, have significant correlation with LTC RWR in south China. But the relationships between surface characteristics and LTC RWR in north China are not statistically significant. It is worth noting that although the correlation between DIV200 and LTC RWR is insignificant for the whole China mainland, it presents highly negative and positive correlations in south and north China, respectively.