Based on the data of the insect trap catches, the entomological radar surveying, and the weather observations in the China, some processes by which the northward and southward migrations through China of the Brown Planthopper Nilaparvata lugens (BPH) occur during July and October in 1991 were picked out. These processes have been investigated with an advanced mesoscale numerical weather-forecasting model, MM5 (V3.2) and the 3D windborne trajectories of BPH's migration were simulated. Some parameters, such a...