Characters Of Low Frequency Oscillation And Its Relationship With Summer Precipitation Of Middle And Low Reaches Of Yangtze Rivers

By using wavelet and bandpass filter methods, the different characters of lowfrequency oscillation (LFO) of OLR and wind field for eight anomalousflood/drought years in middle and low reaches of Yangtze rivers duringMay-August are investigated. The results are as follows: (1) The LFO charactersof OLR and wind field is obvious during 1980-2000. and the 30-60 daylow-frequency character is more distinct in flood years than in drought years; (2)The relationship of low-frequency OLR and zonal wind is greatly different indrought years and flood years. The time of peak value of low frequency u wind isprior to the peak of rainfall in flood years; (3) There are low frequency OLRmoves northward at low-latitude and southward at mid-latitude at the same time inflood years , the join point is between 20-30 N. Contrarily, there isn't clearconfluence area in drought years; (4) The source region is about mid-latitudePacific Ocean and Philippines in flood years and drought years. There are lowfrequency vortex moves northward at low-latitude and southward at mid-latitude;there are low frequency vortex moves northward at low-latitude andsouthwestward at mid-latitude in flood years, it's easily to bring on convergenceor divergence in large-scale and heave rainfall. Further more, the coherencebetween circulation and OLR are calculated and analyzed. The results show thatthere is positive correlation between Australian high and the precipitation ofmiddle and low reaches of Yangtze rivers, and negative correlation betweenOkhotsk and the precipitation of middle and low reaches of Yangtze rivers.