Impact Of Quasi-biweekly Atmospheric Low Frequency Oscillation On Immigration Of Nilaparvata Lugens (St(?)l) In China

Among the effect of atmospheric background of brown planthopper migration(BPH) and catastrophic immigration (or weather conditions), the physical effects of atmospheric motion system in different spatiao-temporal scales (including dynamic effect, thermal effect, water stress, etc.) is the key factors. Through the analysis of weather process, prediction of BPH's immigration amount can prevent the outbreak of BPH disaster. We can also early warn the outbreak of BPH from aspects of the influential weather and climate conditions. So far, there were few works about the extended forecast of BPH's immigration in China and abroad.The daily BPH's light trap data of 105 plant protection stations in China and the daily reanalyzed meteorological data from the National Center of Environment Prediction (NCEP) and the National Center of Atmospheric Research (NCAR)during the period from 1979 to 2015 were collected. Morlet wavelet analysis was used to analyze the cycle characteristic of BPH immigration amount at the representative pest monitoring sites in south China and the regularity of the periodic oscillation of atmospheric physics variables. The correlation between BPH amount and atmospheric physical quantity with low frequency oscillationwas analyzed. The phase analysis was used to analyze the atmospheric physical variables influence on the immigration of BPH phase by phase. The impact of the atmospheric oscillation and its physics variables with the quasi-biweekly low frequency on the immigration of BPH was explored qualitatively. HYSPLIT(Hybrid Single Particle Lagrangian Integrated Trajectory Model) was used to analyze the backward trajectory of the brown planthopper population at the typical sites. The main conclusions were showed as follows:(1) During the study period, the immigrating amount of BPH in the study area had a significant low frequency oscillation signal of 10? 20d and 20?30d.Simultaneously, wind fields, geopotential height fields and vertical velocity fields on the isobaric surfaces of 850hPa and 925hPa appeared the significant low-frequency cycles of 10-20d.The significant correlation existed between the low-frequency oscillation of BPH's immigrating amounts and these atmospheric physical variables.And the low frequency atmospheric physical field was ahead of the low frequency amount of BPH.(2) Under the influence of the low-frequency southwestern wind, the BPH's populations transported from the rice-growing region of southwestern China to the rice-growing region from the Nanling Mountain to the Yangtze River during August to September in 2010. In the later period, the part of BPH's populations immigrated from the rice-growing region between the Huaihe River and the Yangtze River to the rice-growing region between the Nanling Mountain and the Yangtze River under the influence of the low-frequency northeastern wind. Under the influence of the low-frequency Southeastern wind, the BPH's populations transported from the rice-growing region of Southeastern China to the rice-growing region of Ssouth China in July of 2012. In the later period, the part of BPH's populations immigrated from the rice-growing region of Southwest to the rice-growing region of Huanan under the influence of the low-frequency western wind.(3) There was strong downdraft in the rice-growing region of Jiangling of phase 1-2 during August to September in 2010. At the same time,the strong downdraft in rice-growing region of Jianghuai disappear, meanwhile strong updraft in the rice-growing region of Huanan and Jiangxi moved eastward and reduced gradually.The vertical flow on the rice-growing region between the Nanling Mountain and the Yangtze River affected obviously on descent of BPH. On phase 3, strong updraft in rice-growing region of Jianghuai was conducive to take offand BPH fly from north to south. On phase 4,strong updraft in rice-growing region of Jianghuai further enhanced. The vertical airflow field had a weak effect on the northward migration of BPH, while it played a significant role on the southward migration. In July of 2012, vertical airflow in rice-growing region of Huanan had few influence on BPH.The amount of BPH is mainly affected by precipitation.(4) Results of backward trajectory analysis of BPH population was provided to confirm that the insect sources and migration paths of BPH's populations immigrated into the rice-growing region between the Nanling Mountain and the Yangtze River were consistent with the low frequency prevailing wind fields. There was warm and moist airflow transporting from Southwest region to the region between the Nanling Mountain and the Yangtze River, and there was weak northeast wind in region between the Nanling Mountain and the Yangtze River.When it came to phase 2,moist airflow came from Southwest China and South China to region between the Nanling Mountain and the Yangtze River. The population of BPH was still mainly from Southern China and the southwest region, and a few part came from the Jianghuai area. Phase3-4, prevailing wind direction in the study area transformed southerly wind to southeast winds. In July of 2012, rice-growing region of South China prevailed southeast wind,meanwhile warm and humid airflow came from the Indochina Peninsula to South China from phase 1-2. Phase 3-4, prevailing westerly in rice-growing region of South China turned northwest wind. The results of HYSPLIT was coincide with the low frequency wind field.(5) Amog this three models which forecasted the low-frequency immigrating amount of BPH, the maximum prediction error of the BP neural network model and the multiple linear regression model were slightly larger than the support vector machine (SVM) model and the prediction accuracy was unstable, but the ME of the SVM model is the lowest and its prediction accuracy was stable.