The landing mechanisms of brown planthoppers, Nilaparvata lugens (Stl) (BPH) were studied using GIS (Geographic Information System), MM5（The Fifth-Generation Mesoscale Model）and GrADS (Grid Analysis and Display System) synthetically to analyze geographic distribution patterns of immigrated populations of BPH and the atmospheric backgrounds that influenced the landing processes. During the momentous rainfall process from June 22 to July 2 in1999, a typical migration process of BPH occurred in the southern China. The spatio-temporal distributions of the immigration peaks of BPH were analyzed using the data of light trap catches and field survey. In addition, we analyzed the atmospheric backgrounds during the BPH immigration, i.e., the windborn streams, the circulation situations, the weather conditions, and the topographies influenced the immigrations, etc. The landing mechanisms of BPH at Lingchuan, Dongzhi and Huizhou were compared based on topography, precipitation, subsiding airflow etc. The correlations between the population densities of BPH at source areas and landing areas were analyzed by using HYSPLIT, a trajectory analysis software.
We obtained the following results: (1) BPH landed obviously on the two areas in the studied cases: i.e. Landing area I is along Tianzhu (Guizhou Province), Lingchuan (Guangxi Autonomous Region) and Hexian (Guangxi Autonomous Region); and Landing area II is along Sandu (Guizhou Province), Tianzhu (Guizhou Province), Qianyang (Hunan Province), Xiushui (Jiangxi Province), Dongzhi (Anhui Province), Huizhou (Anhui Province) and Fengxian (Shanghai City). (2) The airstream of the low lever jet carried BPH migrating to the north. (3) The landing areas are mainly on the margin of the rainfall zone, at which the precipitation changed from slight to heavy. (4) The orographic precipitation forced massive BPH to immigrate into the landing area I. (5) Whereas, the Bai-u front lead BPH to land massively in the landing area II. (6) The differences of the spatial distribution of BPH and the weather conditions between different locations that BPH took off resulted in the differences between the distribution of BPH that landed at Dondzhi and Huizhou.