SummaryThe t~resent study is conducted in the equivalent barotropic model to study the stability of meridional wind at 200 mb level in tropics during summer. The equivalent barotropic model, which was introduced by Wiin-Nielsen [ 1 ] for midlatitude, is accepted for tropics after some possible changes. The meridional wind is found to be equivalent to a number of superposed dispersive Rossby waves, so the stability problem of meridional flow reduces to the stability problem of Rossby waves. In the present study, the stability of single Rossby wave is tested with a perturbation which gives zonal wind. Itis found that the short Rossby waves are unstable, so the short Rossby waves release their kinetic energy to the zonal wind. Thus, the short waves of the spectral meridional flow release their kinetic energy to the zonal wind. For midlatitude, Lorenz's problem regarding tile instability of Rossby wave is improved using the equivalent barotropic model. Zusammenfassung
SummaryThe object of the present paper is to study the stability of a monsoon depression which is a low level wave disturbance over the Indian region during summer. The stability of a wave disturbance depends intimately on the phase velocity. Again, the phase velocity of Rossby-gravity wave does not explain the phase velocity of a monsoon depression. Thus, knowing that the convective activity plays an important role in the development of a monsoon depression, one modifies the phase velocity of zonally propagating Rossbygravity waves, i. e. one obtains the modified dispersion relation considering the effect of convective heating in the equivalent barotropic model which is derived for the low levels in tropics. The modified dispersion relation explains the phase velocity of monsoon depression. Beyond the limiting stage, there is no further depression of the central pressure. So, it is essential to study the stability of a monsoon depression at the limiting stage. The stability analysis shows that the monsoon depression is neutral (i. e.; does not break down) as long as there is convective activity. But the monsoon depression becomes unstable (i. e.; breaks down) if the convective activity ceases. In the latter case, one obtains a possible stream of zonal wind. Zusammenfassung Die Stabilitiit von MonsundepressionenIn der vodiegenden Arbeit wird die Stabilitiit yon Monsundepressionen untersucht, die durch Wellenst6Iungen in der unteren Atmosph~ire Indiens im Sommer dargestellt werden k6nnen. Die Stabilit~t dieser Wellenst6mngen h~ingt in grot~em Ma~e yon deren Phasengeschwindigkeit ab. Diese jedoch ist nicht mit der Phasengeschwindigkeit yon RossbySchwerewellen identisch. Im Hinblick auf die Tatsache, daft die Konvektion eine bedeutende Rolle in der Entwicklung einer Monsundepression spielt, kann die Phasengeschwindigkeit yon zonal sich fortpflanzenden Rossby-Schwerewellen dahingehend modifiziert werden, daf~ man eine ge~inderte Dispersionsbeziehung ethiitt, welche den Einflut~ konvektiver Erw~irmung in das fiir die unteren Atmosphiirenschichten entwickelte ~iquivaient-barotrope Model1 einbezieht.
SummaryThe mutually interacting pressure wave and diabatic heating wave originally cause the observed tropical disturbances. The equivalent barotropic models relate the tendency of vorticity with the convective heating effect directly, and so these models elucidate the roles of these mutually interacting waves on the development of observed tropical disturbances readily. The exact solution for the complex frequency adequately explains the growth and movement of tropical disturbances during summer. The results are divided into two parts 1) for the upper atmosphere 2) for the lower atmosphere. For the upper atmosphere during summer, the standing and amplifying natures of wave numbers 1 and 2 are satisfactorily interpreted. So the standing natures and the intensity variations of Atlantic trough, African high, Tibetan high, Pacific trough, and Mexican high etc. are also explained thereby. Also, the amplification and westward movement of short wave number 8 are interpreted, For the lower atmosphere during summer, the amplifications and westward movements of Carribean easterly wave, African monsoon cyclone, Indian monsoon depression, west Pacific ITCZ wave etc. are explained. Zusammenfassung Die Entstehung tropischer St6rungen
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