基于两种轨迹模型的褐飞虱迁飞轨迹比较研究

异地预测是迁飞性害虫发生预测的重要内容,迁飞轨迹模拟和预测是能较好地反映害虫迁飞时空动态的一种异地预测方法。褐飞虱作为我国水稻生产上的一种重要迁飞性害虫,其迁飞轨迹的准确预报,可为其灾变预警和有效防控提供科学依据。为了比较选择一些准确性好、分辨率高、易于推广应用的害虫迁飞轨迹模型,选取2006年7月初发生在湖南省洪江市的一次褐飞虱重大北迁过程作为典型个例,运用中尺度天气研究和预报模式WRF,结合NCEP气象再分析数据,利用HYSPLIT和FLEXPART两种轨迹计算模式对褐飞虱迁飞轨迹进行模拟,并验证模型模拟和计算的准确度和精确度。研究结果表明:(1)WRF-HYSPLIT和WRF-FLEXPART两种轨迹计算模式在虫源地、迁飞路径(迁飞方位角和走向)、迁飞高度、迁飞速率和迁飞距离计算上总体趋势一致,但存在一定的差异,后者的起伏变化大于前者。(2)尽管两种耦合模式在调用WRF模式输出的预报场物理变量方面有很多相同之处,但WRF-FLEXPART耦合模式在运行计算过程中比WRF-HYSPLIT耦合模式多考虑了对流参数、地表胁迫和各种地形参数,因而能更全面地反映中尺度天气过程(特别是对流性天气过程)对昆虫起飞、空中飞行和降落的动力作用,也能更真实地反映地表物理过程、大气湍流结构和地形起伏对褐飞虱种群迁飞的影响。(3)从褐飞虱种群对生境和取食条件选择上看,两种模式模拟的各高度迁入种群的虫源区、迁飞路径和降落地都是合理的、准确的。但从褐飞虱迁出、空中飞行和降落所处的三维流场来看,WRF-FLEXPART模式轨迹走向与盛行气流方向的吻合度要明显高于WRF-HYSPLIT模式。(4)两种模式均可作为业务工具在迁飞性害虫测报中推广应用。

Comparative study of migration trajectories of the brown planthopper, nilaparvata lugens (Stål), in China based on two trajectory models

Exotic prediction is an important content for predicting the occurrence of migratory pests. The simulations and prediction of the migration trajectory of pests is considered an ideal exotic prediction method that can reflect the spatio-temporal dynamics of the pest''s migration. The brown planthopper (BPH), Nilaparvata lugens (Stål), is an important migratory pest that affects rice production in China and the accurate forecasting of its migration trajectory can provide a scientific basis for the early warnings and effective prevention of pest-related catastrophes. In order to select appropriate pest migration trajectory models with good accuracy, high resolution, and easy popularization, we screened a great northward migration event of BPH that occurred in Hongjiang City of Hunan Province at the beginning of July in 2006, as a typical case of BPH migration in China. The Weather Research and Forecast (WRF) Model, a popular mesoscale weather research and forecast model used both at home and abroad, was used to simulate and output the atmospheric background fields in high resolution combined with re-analyzed meteorological data from the National Center of Environment Predicting of the USA (NCEP). The forecasting variable fields output by the WRF model as meteorological inputs to drive the two trajectory models were coupled with the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) Model and the Flexible Particle (FLEXPART) Dispersion Model to predict the migration trajectories and landfalling areas of BPH populations. According to the backward calculation results, the differences between some trajectory parameters of the two models, such as the pest sources, migration paths, migration heights, migrating speeds and migration distance, were compared. Finally, the observed data for the habitat, feeding conditions, and three-dimensional atmospheric airflow fields of BPH''s migration were used to verify the accuracy and precision of the simulations and calculations. The results suggest several important points. First, the two models show good consistent performance on the calculations of pest sources, migration paths (migration azimuth and flight direction), migration heights, migrating speeds and migration distance. However, the variations in the migration parameters in the FLEXPART model are larger than those in the WRF-HYSPLIT model. Second, as compared to HYSPLIT, the FLEXPART model can better represent the dynamical role of meso-scale weather especially convective processes in the migration processes such as takeoff, flying duration, and landing location, and more realistically simulate land surface processes, atmospheric turbulence structure, and undulating terrain and their impact on the migration of BPH populations. This is because the FLEXPART model has included more realistic parameterization schemes for convection, surface stress, and complex terrain in the trajectory calculations, whereas the HYSPLIT model does not. Third, the two models present reasonable simulations on pest sources, migration paths, and landfalling areas in terms of the selection of BPH populations for habitats and feeding conditions. However, the trajectories simulated by the FLEXPART model showed better agreement with the prevailing winds than the HYSPLIT model''s simulations. The evidence can be seen from the three-dimensional airflow fields in which the emigration, flight, and landfalling of BPH populations occurred. Fourth, both HYSPLIT and FLEXPART models demonstrated strong operational forecasting capabilities of migratory pest occurrence.