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Introduction

The traditional view in climate has been that the stratosphere can only play a limited role in climate change. However, there has been increasing evidence in recent years that the stratopshere is a sensitive component of the climate system, which can affect the troposphere through coupling mechanisms.

There are three principal mechanisms by which the stratosphere can affect tropospheric climate. The first is through radiative transfer, either by changes in the amount of solar radiation that reaches the surface (e.g. after a volcanic eruption), or by changes in the amount of downwelling longwave radiation emitted by the stratopshere (e.g. because of stratospheric ozone depletion). The impact depends very sensitively on the vertical, latitudinal and seasonal structure of the changes in radiatively active substances, particularly in the vicinity of the tropopause. (Forster et al. 1997; Hansen et al., 1997).

The fact that the distribution of the radiatively active substances is controlled by the Brewer-Dobson circulation together with quasi-horizontal in mixing into the lower stratosphere emphasizes that climate models need to represent these processes with sufficient fidelity in order to capture this sensitivity.

The second and third mechanisms by which the stratosphere can affect tropospheric climate take account of the basic dynamical fact that tropospherically forced waves propagate up, while zonal mean anomalies propagate down. Thus, the second mechanism is that the stratosphere can affect the "upper boundary condition" of troposphere by affecting the propagation characteristics of tropospheric waves. The possibility goes back to the classic work of Harney and Darzin, but there has been remarkebly little investigation on this issue in recent years. The possibility of wave reflection at the tropopause has obvious implications for regional climate purtabations.

The third mechanism is then the downward propagation of zonal-mean anomalies, whose mechanism is ‘downward control’. Such downaward influence has been seen in model studies (Kodera et. al., 1996).

In view of the above, therefore, the present work presents an analysis of the temporal characteristics of the convection and ENSO versus Total ozone relationship over Kenya in East Africa.