Study On Space-Time Characteristics Of Anomalous Winds Over East Asian Monsoon Region At Low Altitudes

By using the method of vector empirical orthogonal function (VEOF) and winds data of long time series, anomalous monsoon wind over east Asian monsoon region are analyzed. Dominant modes are obtained for the research of annual and decadal oscillations.Some methods included:1) The method of EOF is used for changing a spacing field to a series spacing and time modes of orthogonal, from which we can get characteristic of space and time about ocean and air. Now, we can get the EOF mode by using the method of SVD.2) The methods of spectrum analysis and filtering, such as Butterworth filter, are used for seeking the interannual and decadal variation of east Asian monsoon, and its connection with ENSO.The data provided from NCEP/NCAR is about month mean winds field, which from Jan 1950 to Dec 2004. its precision is 2.5°×2.5°, and the area is chosen on 0°～50°N,100°～150°E.Some result can be concluded, the first mode of anomalous monsoon wind belongs to ENSO-connected mode. The time mode have high active relation with ENSO, and it lags ENSO course 6～8 months, when relation can get the notability. East Asian monsoon over tropic and semi-topic area have important connection with ENSO movement. We put forward a notational type between them.Cumulative covariance rate which from the first mode to the sixth mode get 60%, which can represent the dominant flow pattern basically over east Asian monsoon winds field.(1)The low frequency of anomalous monsoon wind over east Asian monsoon region have a period of 2～4 years, and the period of 11～20 years is induced from the modes of the second,fourth and the sixth.(2) The first mode of anomalous monsoon wind over east Asian monsoon region is an typical mode from summer to winter, the time series of which have a important connection with Nino3 index, and the best lag time between former and latter is 6～8 months.The method of VEOF can open out space-time variety of anomalous monsoon better, the significance of climate of which is intuitionistic and clear.The first mode of anomalous monsoon wind belongs to ENSO-connected mode, the time mode of which has high relation with ENSO. It lags ENSO course 6～8 months, when relation can get the notability. it can be explained like this: the couple frequency is induced from them, and the continuous increasing (decreasing) of sea surface temperature about east Pacific over equator can weaken (strengthen) the first mode. It is worthy of further research over the connection between the east Asian monsoon and ENSO.