Abstract

A feature of the time averaged tropical lower stratospheric upwelling is the double peak structures centred near 70 hPa and 20° N-S which have previously been noted in observational datasets. However, the corresponding structures in diabatic heating rates are not related to local temperature anomalies as would be the case if they were relaxational in nature. We will first demonstrate that the enhanced diabatic heating near the centre of these peaks relative to the Equator arises predominantly from the meridional structure in ozone concentrations. We then suggest that the primary cause of the peaks in upwelling is the externally imposed part of the radiative heating field which is able to change the wave field. This motivates the second part of this study in which a scaling argument shows that an externally imposed zonally symmetric heating can indeed drive steady-state upwelling provided that the wave force (required to satisfy angular momentum constraints) is sufficiently sensitive to changes in the mean flow. The applicability of this regime to the observed double peak structure is confirmed by experiments in a dry dynamical circulation model. Similar arguments are then be applied to problem of the recently identified compensation between the driving of the Brewer-Dobson circulation by resolved and parameterized waves.