Climate Signal Detection Analysis Of Anomalies In The Middle And Lower Reaches Of The Yangtze River Precipitation

A new method─MTM-SVD of climate analysis was introduced and its theories andcharacters were discussed in this issue, we compare the differences and features with thenormal EOF,SVD,spectrum analysis and wavelet analysis on theories and functions. Beingused for examples of application, we use the MTM-SVD method to analyze the coupledrelationships between the precipitation over Mid-lower reaches of Changjiang River andSST over the North Pacific, SLP field over the Northern Hemisphere, 500hPa height fieldover the Northern Hemisphere from January, 1951 to December, 2000, and the influenceswhich caused by abnormally interdecadal changes and interannual changes ofOcean-Atmosphere in the recent 50 years on the precipitation over Mid-lower reaches ofChangjiang River were analyzed. The results show that the features of the MTM-SVDmethod are: (1) It can be used to analyze the spectrum characters of climatic variables veryconveniently. For including the MTM method, in which the time series are multiplied byseveral tapers, there will be building an optimal trade-off between spectral resolution andvariance,preventing the leakage in spectrum analysis and wavelet analysis effectively, sothe results are more rich and more real. (2) It can be used to reconstruct spatiotemporalsignals for variable fields. This reconstruction of signals on different frequencies candescribe the oscillation modes of the evolutive process in a more intuitionistic way than thesingle spatial or temporal mode. Meanwhile, the variable amplitude and phase of thetemporal pattern represent the varying envelope of the oscillatory signal. (3) TheMTM-SVD technique can also be extended for its application to coupled fields, that is, tomore than one field at a time. We can obtain the correlativity between the coupled fields byreconstructing the spatial and temporal patterns. We make use of the MTM-SVD method toanalyze the changing characters of the precipitation over Mid-lower reaches of ChangjiangRiver in different time scales,the results show that we can detect the remarkable oscillatorysignals in different time scales obtained by the maximum entropy spectrum analysis andwavelet analysis efficiently only by using this method and prevent the spectral leakage withthe farthest restrictions. The precipitation over Mid-lower reaches of Changjiang River hasnot only a quasi-biennial oscillatory periods equals to the atmosphere oscillation but alsohas an oscillatory periods related to the ENSO circulation and interdecadal oscillation atabout 16～18a. By using the spatial and temporal reconstruction in interdecadal scalebetween the precipitation over Mid-lower reaches of Changjiang River and SST, SLP,500hPa height fields to analyze the coupled characters between precipitation and these threevariable fields. According to the interdecadal scale, when the North Pacific presents a warmphase trend of PDO structure, while the SLP over the Northern Hemisphere presents aremarkable opposite structure of the negative phase in high-latitude and positive phase inmid-latitude, and the positive and negative centers present regular wave trains at 500hPaheight field over the Pacific, these indicate high possibility that it was raining overMid-lower reaches of Changjiang. The coupled relationships in interannual scale betweenthe precipitation over Mid-lower reaches of Changjiang and SST, SLP, 500hPa height fieldsshow that the abnormal changes of the phase of the East Pacific SST, NAO, NPO, theabnormal changes of the intensity of the polar vortex and the West Pacific Ocean subtropicalhigh pressure are the signals of the abnormal changes of the precipitation over Mid-lowerreaches of Changjiang.