Madden-JulianU“ฎ‚ฬ\‘ข‚ฦˆส‘Š‘ฌ“x‚ฬ‰๐อ
An analysis of the structure and the phase speed of the Madden-Julian oscillation

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Žw“ฑ‹ณŠฏF@ˆษ“ก@‹v“ฟ



@The Madden-Julian oscillation (MJO) is one of the most remarkable oscillations in the troposphere. However, the mechanism is still unclear. There may be two clues in understanding the MJO; what controls the eastward propagation and what regulates the slow phase speed? The object of this study is to close in on these clues. For the former purpose, the spatial structure is examined, while characteristics of the MJO in different oscillation periods are extracted for the latter purpose. The OLR and NCEP/NCAR Reanalysis datai1980|1998j@are used.

@The relationship among the OLR, latent heat flux and moisture convergence in the spatial structure is investigated by the correlation analysis. The result shows that the low-level moisture convergence (the latent heat flux) exists east (west) of the cumulus active area. Thus, the low-level moisture convergence can be thought to contribute strongly for the eastward propagation of the convection area.

@Next, the oscillation period is classified into three period bands based on the time coefficients of the first and second EOF modes, and then differences in the characteristics of the MJO among these three bands are investigated. It is found that for the different oscillation periods, there are systematic differences in the phase speed, the propagation course and distance, and the meridional extent of physical quantities such as the OLR. It is shown that as the oscillation period is longer, the land over the progress course increases and the phase speed becomes slower. Furthermore, at El Nino events, there are some cases when OLR signals propagate eastward in the eastern Pacific, and the phase speed becomes much faster. From these facts, it is conjectured that the land gives a great influence on the slow phase speed of the MJO.