Case Study: Atmospheric Background For Great Immigration Events Of The Brown Planthopper(Nilaparvata Lugens St(?)l)

The Brown Planthopper(Nilaparvata lugens Stal) is a kind of important pest which have been endangering rice growth in China and some other countries and regions in Asia. It has the qualities of migration in long distance and outburst endangers. In China, the brown planthopper survive and endanger in the tropical regions of the southern Guangdong Province and the southern Guangxi Municipality, the southern Yunnan Province and Hainan Island during winter in every year. In the early spring, with the establishment of the monsoon, large brown planthopper moved from the Indo-China peninsula China, and mainly endanger the southern China. In the interim period from spring season to summer season of every year, BPH's populations migrations northward again, land and endanger the greater part of the austral regions of Yangtze Valley in succession. During midsummer, they migration into area between the Yangtze Valley and Huaihe River or the boreal regions, land and jeopardize Chinese main rice-growing regions. At the end of summer and the beginning of autumn of every year, the migrations backward launch. After it, the similar landing and imperiling processes turn round. This kind of migrations northward and southward, landing and endangering processes brings to the greatest loss of rice production in China. Because of the migrate process is a complicated behavior, except the physiological and ecological mechanisms of the pest itself, the environmental backgrounds, particularly atmospheric backgrounds, had to be considered, so far, many academics at nation and abroad to study more or less related to the impact of atmospheric circulation, but rarely a comprehensive and thorough analysis, according to it, early research started, but progress has been slow. In view of the current research in this area, this study select two processes of the end of August 2006 to early September in the eastern part of the country for rice brown planthopper large-scale move into the process as the major subjects, using the mesoscale meteorological model -- WRF model, focusing on the impact of atmospheric brown planthopper moving dynamic weather systems, as well as key background, the main findings are as follows:In the 26th to 28th Aug. in 2006 process, was analyzed topographically under the assistance of ArcGIS9.0. Based on this analysis, a model with the high tempo-spatial resolution, WRF V2.2 (The Weather Research and Forecasting Model for version 2.2) were used to simulate the weather background of this process numerically and the horizontal wind field, K index distribution, A index spatial pattern and vorticity field on 850 hPa isobaric surface which could reflect the atmospheric dynamical characteristic in the background were selected. After the analysis of these atmospheric dynamical fields, the results were showed as followed: (1) It was appropriate to using the directions of air streams on the 850hPa(approximately 1500m) to describe the flight directions of BPH' populations in the main migrant layers (2) During the cardinal landing periods of BPH' immigrating populations, the spatial patterns of K index and A index on 850 hPa isobaric surface displayed the atmospheric instability and indicated the distribution of the main landing regions of BPH' populations qualitatively. When K≥35℃,A≥10℃or both indexes met their above corresponding value, the development of the atmospheric vertical movement was favorable and it was advantageous to the taking-off and landing of BPH's populations. (3) When the pests immigrated massively into some regions, some concurrent negative vorticity with the higher values or the lower value appeared in these regions. It showed that there were the sinking airflows with certain strength in the regions. These sinking airflows were available to the landing of BPH.WRF V2.2 (The Weather Research and Forecasting Model for version 2.2) was used to simulate the weather background of this immigrating process numerically(the 30th to 31st Aug. in 2006 process was picked). According to the exported simulations, the migrating trajectories of the BPH's populations were reckoned backward and the migrating heights in the different hours were calculated. Consequently, a key weather system, the subtropical high in the West Pacific Ocean influenced on the migration and landing of BPH's populations and the horizontal stream field and vertical velocity structure on the related regions were analyzed. The results were showed as followed:(1)In this migration, the immigrating BPH's populations landing on the rice-growing regions of the upper Yangtze River Valley were come from the area conjoined the northern Guangxi Municipality, the southeastern Guizhou Province, the southern Hunan Province and the northwestern Guangdong Province in succession and the populations landing on the middle reaches and downstream of Yangtze River Valley had two pest source areas which one of the pest source was the rice-growing regions of the southeastern Hebei Province and the southwestern Anhui Province and the another source was the Huaihe River valley.(2)The flight height of BPH's populations in this event were from 900m to 2100m mostly and migrant routes and distances changed with the horizontal airflows and vertical velocity fields.(3) The short-term oscillations of the subtropical high in the West Pacific Ocean was a key factor brought about the BPH's catastrophic immigration in this period. The area flex of the subtropical high and the changes of the vertical velocity in its continental pivotal regions on the isobar surfaces of 500hPa and 850 hPa had an important influence on the areas, times and heads of BPH's landings. The horizontal airflow directions around the western side and northern side of the subtropical high on 850hPa isobaric surface could reflect the migrating paths of BPH's populations in the air. (4) The short-term oscillations of the subtropical high brought a serious of the important influences to the catastrophic immigrations of BPH and it proclaimed that the subtropical high, as a large-scale atmospheric circulation system, can engender different dynamical coerces on BPH's immigrations in different tempo-spatial scales.