Comparative analysis of the water vapor paths and sources for different heavy rainfall regions during Typhoon Lekima (1909)

As water vapor is essential for typhoon precipitation, exploring its origins is

important for understanding the evolution of these precipitation events. This study uses Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT) which is driven by the data from the fifth generation atmospheric reanalysis data of the European Center for Medium-Range Weather Forecasting, and the areal source receptor attribution method. The differences and their causes of atmospheric circulations, water vapor paths and contribution of two centers of precipitation in Zhejiang and Shandong during Typhoon Lekima are analyzed. The results are as follows. (1) From the perspective of atmospheric circulation, water vapor of the precipitation in Zhejiang is mainly transported by the southwesterly water vapor channel and the easterly airflow to the north of Typhoon Krosa. As the southwesterly airflow weakens, the water vapor for the precipitation in Shandong is primarily supplied by Pacific water vapor via the easterly airflow to the north of two typhoons. (2) There are four main moisture paths responsible for precipitation in Zhejiang, respectively from the eastern Pacific Ocean, Australia, the western Pacific Ocean and the Indian Ocean, while there are three main moisture paths for precipitation in Shandong, respectively from the eastern Pacific Ocean, the Indian Ocean and the western Pacific Ocean, with the proportion of the eastern Pacific path increasing to 51.7%. The main reason for the difference of the water vapor path is the weakening of the southwesterly wind, which led to a reduction in trajectories from the Indian Ocean and Australia, while the easterly wind to the north of the two typhoons increased the proportion of Pacific transport pathways. (3) Regarding water vapor contribution, the primary source regions for Zhejiang are the Pacific (33.1%) and Australia (15.3%), mainly due to the high trajectory frequency and high moisture conversion rates from these regions. The water vapor contribution from the Pacific Ocean is the highest for the precipitation in Shandong, at 73.8%, attributed to a high trajectory frequency and a high moisture uptake ratio of 80.8% among air parcels originating over the Pacific Ocean. Therefore, water vapor pathways and sources vary across different stages of the same typhoon. These findings can enhance the understanding of water vapor sources and provide valuable references for predicting precipitation locations during typhoon events.