【摘要】 为研究2011年春夏长江中下游地区旱涝急转现象与低频环流的关系,利用国家气象信息中心的753站逐日降水、NCEP/NCAR再分析资料和带通滤波的方法,得到如下结果:(1)2011年5~6月,长江中下游地区存在明显旱涝急转现象,5月的降水较同期偏少40%以上,6月的降水较同期偏多60%。(2)5~6月的旱涝急转前后,长江中下游地区的500h Pa的垂直速度变化不仅与降水有很好的关系,而且其低频振荡的强度也显著加强,垂直速度由正(下沉运动)转负(上升运动)的转换时间几乎对应由旱转涝的时间。(3)对旱涝急转过程的500h Pa低频变化垂直速度下沉运动最强、下沉运动向上升运动转换、上升运动最强3个位相的低频散度场分析发现,在5月干旱期间,长江中下游地区维持对流层低层(850h Pa)辐散、高层(200h Pa)辐合的低频环流系统,不利于降水。到6月强降水期,长江中下游地区则迅速转为对流层低层辐合、高层辐散的低频环流系统,有利于降水的发生。这种对流层低层-高层低频环流系统的变化是导致旱涝急转的重要原因之一。更多还原

【Abstract】 Study has been made on the relations between the drought-flood abrupt change phenomenon and low frequency circulation happened over the middle-lower reaches of the Yangtze River in the spring and summer 2011,by using the753 meteorological stations daily precipitation of the National Meteorological Information Center and the NCEP / NCAR reanalysis data. Results show that:( 1) in May2011,there’s 40% less rainfall occurred than in the same period over the middle-lower reaches of the Yangtze River,but there’s 60% more rainfall in June 2011. So the drought-flood abrupt change phenomenon can be obviously seen.( 2) Before and after the drought-flood abrupt change,the 500 h Pa vertical velocity of the middle-lower reaches of the Yangtze River not only has a good relationship with precipitation,but also its amplitude of the low frequency oscillation is intensified obviously.( 3) It is analyzed that the low-frequency divergence of the three phases during the strongest sinking speed,sinking speed to rising speed conversion and the strongest rising speed of the 500 h Pa vertical velocity low-frequency rhythms. Which is found that,before( after) the drought-flood abrupt changes,there is the quickly shift of the low-frequency circulation systems of the 850 h Pa divergence( convergence)and the 200 h Pa convergence( divergence) over the middle-lower reaches of the Yangtze River. Therefore,the transition of the low-frequency circulation systems between the lower and upper troposphere is one of the important cause of the drought-flood abrupt changes in spring and summer 2011.更多还原