Intraseasonal variations in the tropical Western Hemisphere and the generation mechanism of stratospheric Kelvin waves

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Four problems about the atmospheric response to tropical heating were tackled using numerical models based on the primitive equations on the sphere. The model heating was given as an external forcing.The first problem is to clarify the role of nonstationarity in the response to stationary heating. For this purpose, time integration and stationary models are constructed. In parameter ranges for which stationary solutions are unstable, results from the both models show a significant difference in anomaly fields. That is, the time mean yielded from the time integration model has larger amplitudes than the stationary solution. Further, Rossby wavetrains radiating from the tropical heat source go through the midlatitude, again returning to the tropics. Thus, wave amplitudes become large even in regions which are far from the heat source.Next, we examine the role of the tropical-extratropical interaction in the intraseasonal variation. Heating in this model moves from 60E to 180ﾟ, having the … More period of 40days. When there is no tropical-extratropical interaction, i.e., the zonal mean flow in midlatitudes is weak, the amplitude of the intraseasonal variation is large only near the heat source centered 120E. In contrast, when the midlatitude westerly is strong, wavetrains starting from the tropics pass through the midlatitude, returning to the tropics. Then, the intraseasonal variation amplifies in the Western Hemisphere.Variations of the atmospheric angular momentum (AAM) are also examined in the same model. It is found that the source of the AAM associated with the intraseasonal variation does not lie in the equatorial region but the subtropics. The equatorial region is the apparent source, since the AAM is transported from the subtropics to the equator. It is also clarified that Rossby wavetrains play an important role in the acquisition and transportation of the AAM.Finally, numerical experiments are performed, in order to examine the hypothesis that stratospheric Kelvin waves are generated from the tropospheric intraseasonal variation in the Western Hemisphere. We have not so far obtained a positive result about this hypothesis. Less