The southwesterly low-level jet （LLJ） over southeast China in the summer of 2003 is analyzed in this study. The analysis is based on the National Centers for Environmental Prediction （NCEP） Final （FNL） operation...The southwesterly low-level jet （LLJ） over southeast China in the summer of 2003 is analyzed in this study. The analysis is based on the National Centers for Environmental Prediction （NCEP） Final （FNL） operational global analysis data on 1.0-1.0-degree grids at 6-h intervals. The major criteria for choosing the LLJ ineluded the following： a maximum wind speed equal to or greater than 12.0 m s-1, a wind direction of between 180° and 270°, and the height of wind maximum at 900-700 hPa, not confined to single pressure level. The results show that the LLJs over southeast China dominate at 850 and 800 hPa. These LLJs are closely associated with the topography of this area and tend to locate regions with large terrain gradients, including the northeastern and eastem Yunnan-Guizhou Plateau. Under the influence of mid-latitude westerly winds, the LLJs above 750 hPa move northward to the Yangtze-Huai River Basin. Com- pared to the ten-year （2000-2009） mean climate condi- tions, the LLJs in the warm season of summer 2003 were exceptionally active and strong, as reflected by the posi- tive anomalies of LLJ occurrence numbers and wind speed. In addition, the 2003 LLJs showed strong diurnal variation, especially at pressure levels below 800 hPa. The majority of the LLJs appeared between midnight and the early moming hours （before 8 a.m.）. Finally, the summary of LLJ grid numbers indicates that more than 80% of LLJs in June and July 2003 occurred within the 33-d rainy period. Thus, these LLJs are directly related to the anomalously heavy rainfall in the Yangtze-Huai River Basin.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 40905049)the National High Technology Research and Development Program of China (863 Program, Grant No. 2010AA012304)+1 种基金the China Mete-orological Administration for the R&D Special Fund for Public Welfare Industry (Meteorology) (Grant No. GYHY200906020)the State Key Laboratory of Numerical Modelling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) State Key Laboratory special fund
文摘The southwesterly low-level jet （LLJ） over southeast China in the summer of 2003 is analyzed in this study. The analysis is based on the National Centers for Environmental Prediction （NCEP） Final （FNL） operational global analysis data on 1.0-1.0-degree grids at 6-h intervals. The major criteria for choosing the LLJ ineluded the following： a maximum wind speed equal to or greater than 12.0 m s-1, a wind direction of between 180° and 270°, and the height of wind maximum at 900-700 hPa, not confined to single pressure level. The results show that the LLJs over southeast China dominate at 850 and 800 hPa. These LLJs are closely associated with the topography of this area and tend to locate regions with large terrain gradients, including the northeastern and eastem Yunnan-Guizhou Plateau. Under the influence of mid-latitude westerly winds, the LLJs above 750 hPa move northward to the Yangtze-Huai River Basin. Com- pared to the ten-year （2000-2009） mean climate condi- tions, the LLJs in the warm season of summer 2003 were exceptionally active and strong, as reflected by the posi- tive anomalies of LLJ occurrence numbers and wind speed. In addition, the 2003 LLJs showed strong diurnal variation, especially at pressure levels below 800 hPa. The majority of the LLJs appeared between midnight and the early moming hours （before 8 a.m.）. Finally, the summary of LLJ grid numbers indicates that more than 80% of LLJs in June and July 2003 occurred within the 33-d rainy period. Thus, these LLJs are directly related to the anomalously heavy rainfall in the Yangtze-Huai River Basin.
