Atmospheric Dynamics Analysis and Simulation of the Migration of Fall Armyworm

After the invasion of fall armyworm (Spodoptera frugiperda) in China at the end of 2018 or at the beginning of 2019, it spreads rapidly and becomes a seasonal migrating pest that seriously threatens the maize production in China. The long-distance migration of adult fall armyworm is closely related to the seasonal changes of atmospheric circulation in East Asia. The atmospheric circulation and low layer wind dynamic condition that influence the migration of fall armyworm in 2019-2021 are analyzed, and 4 typical weather processes beneficial to the migration are selected to simulate the migration path and landing point with Hybrid Single-particle Lagrangian Integrated Trajactory(HYSPLIT) model. The results show that, during the northward migration of fall armyworm in spring and summer, the strength of the southwest airflow is different due to the varying strength, location and westward extension of the Northwestern Pacific subtropical high(WPSH) in each year, and therefore the low layer wind driving the migration of fall armyworm to transition region and main corn planting area is different. The earlier onset of the South China Sea summer monsoon in May of 2019 is conducive to the early migration from South China into the middle and lower reaches of the Yangtze. June is a key stage for the fall armyworm migration to northern summer maize area, and further spreading to the spring maize area in North China. The west ridge point positions of WPSH from June to July varies in different year, and leads to different northernmost landing position of the pests, which is attributed to the south airflow carrying fall armyworm on the western side of the WPSH. The dynamic conditions of low layer wind during August to September are different in 2019-2021, which vital to the migration to main spring maize producing areas in Northeast China. In 4 simulation cases, 3-weather-process simulations are effectively monitored and verified, indicating the migration path and landing point of fall armyworm. However, in January of 2022, there are some misreports landing point in Guizhou and Fujian, though the southwest low level jet is favorable. HYSPLIT model is effective in the flight trajectory simulation, but it has some uncertainty in the migration distance, time and landing point due to biological characteristics, topography, microclimate, etc. In future, the simulation model should be improved by combination of real-time radar monitoring and other means.