ISSN 1006-9895

CN 11-1768/O4

The Modulation of Madden-Julian Oscillation on Typhoons in the Northwestern Pacific Ocean
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    Abstract:

    The RMM (Real-time Multivariate MJO) index from RMRC (bureau of meteorology research centre) of the Centre for Australian Weather and Climate Research is used to study the modulation of the Madden-Julian Oscillation (MJO) on the typhoon activity over the northwestern Pacific Ocean area and its possible mechanism. The RMM index serves as a proxy for the MJO. It not only can describe the strength of the MJO, but also can reveal the spatial distribution characteristics with the phase categories. It divides the MJO process into eight phases.  The MJO modulation effect on typhoon genesis is quite significant. From June to October, the typhoon genesis cases during strong MJO period are 2 times of those during weak MJO period. In the strong MJO period, there are different typhoon genesis distribution patterns due to different MJO activity phases. The total genesis cases during phases 2 and 3, in which the convection centers are over the equatorial eastern Indian Ocean, are also 2 times of those druing phases 5 and 6, during which the convection centers are over the northwestern Pacific Ocean. After the statistic analysis, the composite method is used to study different atmospheric circulation patterns associated with different MJO phases. The result shows the dynamic typhoon-influencing factors are quite different between phases 2-3 and phases 5-6. During phases 2 and 3, the dynamical factors suppress the typhoon to happen, but during phases 5 and 6, they create a favorable environment circulation for typhoon genesis. It can be inferred that the large scale dynamical environment changes as the MJO convection propagates eastward, which plays an important role in the typhoon genesis.  Convection is a very important factor to both the MJO and typhoons. The composites of the horizontal and vertical convective heating distributions according to different MJO phases are studied. The result shows that in different phases, the heating sources are quite different, which would definitely lead to different change from effective potential energy to effective kinetic energy. In combination with the convergence and divergence of the moisture transport fluxes, the modulation of typhoon genesis by MJO can be revealed from the energy aspect.

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  • Online: December 06,2011
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