The Physical Mechanism Of The IIE Interannual Variation With The Simplified Dynamical Model

With the global atmospheric circulation reanalysis data provided by NOAA/OAR/ESRL PSD, given the maximum zonal wave number as8, the maximum meridional wave number as2, and the truncated spectral functions as sinkxsinly, cos kxsinly and cosly, based on the least-square method, the specific form of the basis functions which best describe the atmospheric flow field in early summer spanning1979to2008are determined. Among all basis function combinations, the zonal wave number1is prominent, and thus based on them, the swing angle of the flow field has been calculated and compared with the index of the interface between the East Asia summer monsoon and the India summer monsoon (IIE). The correlation coefficient of the standardized atmospheric circulation swing angle and the HE standardized series is0.309, with60%symbol accuracy rate. This indicates that the variation of the large scale atmospheric circulation is consistent with the HE zonal movement as a whole. In order to further reveal the physical mechanism of the IIE inter-annual variation, with the spatial spectral functions selected with the reanalysis data, the improved low order spectral model and the2-layer baroclinic model have been employed. The characteristics of the equilibrium evolution representing the atmospheric circulation spanning every year in the research have been analyzed, based on the corresponding differential equation system. It turns out that significant wave-wave and wave-flow interactions exist in the differential equations representing the atmospheric circulation of many research years. And it is also found that the majority of the years with abrupt changes are either the IIE anomaly years or the years with large IIE fluctuation, whereas the evolutionary processes of the atmospheric circulation of the IIE normal years do not contain bifurcation. Given the external thermal forcing parameter, the1st wave swing angle of the atmospheric circulation has been calculated. If the calculation only involves the equilibrium, the correlation coefficient between the1st wave swing angle and the standardized IIE index is0.327, and the symbol accuracy rate is67%. As the same basis function set may be selected by the observational data in some years, in order to obtain different evolutionary processes of the atmospheric circulation in these years, the corresponding regression coefficients are considered in the spectral expansion. The swing angle of the flow field is calculated considering both the regression coefficients and the equilibria of every research year, whose correlation coefficient with the IIE index is0.329, and the symbol accuracy rate is also67%. The above three calculations of the1st wave swing angle illustrates that both the initial state and the evolution of the atmospheric flow field affect the eastward and the westward movement of the HE, however, compared with the influence of the initial state, the effects of the internal dynamics processes are more significant. The main internal dynamics process of the IIE zonal movement inter-annual variation is that the evolution of the atmospheric circulation with abrupt changes tends to cause abnormal HE zonal movement, which appears as the positive and negative anomaly years of the IIE index, as the external thermal forcing transforms from the winter pattern into the summer pattern. The evolution of the flow field in the form of the gradual changes confines the IIE eastward and westward movement, which shows itself as the normal years of the IIE index.