华南前汛期典型旱涝年降水的低频特征及其与冷空气的关系

利用国家气象信息中心提供的1961—2010年华南85站逐日降水及NCEP/NCAR逐日再分析资料,选取2004、2010年为华南前汛期降水典型旱、涝年,分别统计旱涝年降水及冷空气低频特征,讨论低频冷空气与低频降水的关系,并揭示低频冷空气信号源地。结果表明:(1)涝年降水存在10～20 d和30～60 d显著低频周期,旱年还存在20～30 d低频周期。无论旱涝年,低频位涡与同频域降水呈显著的正相关关系,其中10～20 d低频位涡与同频域降水的关系最为密切;(2)涝年华南前汛期10～20 d低频冷空气直接源地位于华北至渤海一带,南传特征明显,高层冷空气源地位于平流层低层西西伯利亚地区,高层高位涡空气沿315 K等熵面向低层输送,干侵入为西北路径。旱年对流层低层冷空气传播特征不明显,高层冷空气源地位于平流层低层东北地区,由于高低层位涡传输通道断裂,导致冷空气活动减弱,降水减少,干侵入为东北路径。

Study on the low-frequency features of precipitation in serious flood and drought pre-flood seasons over South China and its relationship with cold air

85-station daily precipitation data provided by the National Meteorological Information Center and NCEP/NCAR reanalysis data from 1961-2010 are used to select 2004 and 2010 as the serious drought and flood year of pre-flood precipitation over South China. The low-frequency characteristics of precipitation and cold air and their relationship are also be investigated. The main results are as follows:(1)The pre-flood season precipitation in flood year is mainly controlled by 10-20 d and 30-60 d oscillation. In drought year, 20-30 d is another significant low-frequency cycle. The low frequency potential vorticity has positive correlation with the same frequency precipitation, especially for 10-20 d low frequency potential vorticity. (2)For the flood year, the direct source of the 10-20 d low frequency cold air locates from the North China to the Bohai Sea area. Inclined 315 K isentropic surfaces from west Siberia region are the areas where vertical vorticity grows quickly most easily, it is also the path along which the upper cold air intrudes. For the drought year, there is little cold air transportation in the lower troposphere. 10-20 d low-frequency precipitation is influenced by the high potential vorticity pools which exists in upper troposphere (lower stratosphere) is the main source.