2.3 Back-trajectory analyses
The HYSPLIT model (NOAA, https://www.ready.noaa.gov/HYSPLIT_traj.php) was developed to calculate and analysis the transport trajectory of atmospheric pollution or water vapor towards or from a set location (Stein et al., 2015). The atmospheric air masses of precipitation were simulated by a back-trajectory analysis, and the NCEP Global Data Assimilation System (GDAS) database was selected for each back-trajectory of 72 h. Normally, convective activity raise the typhoons to greater heights. Hence, the starting heights of water vapor trajectories were taken to be 500, 1000, and 2000 m above mean sea level.