Scale sensitivity of the Gill circulation, Part I: equatorial case

We investigate the steady dynamical response of the atmosphere on the equatorial β-plane to a steady, localized, mid-tropospheric heating source at the equator (Part II investigates the off-equatorial case). Expanding Gill (1980)’s seminal work, we vary the latitudinal and longitudinal scales of the diabatic heating pattern while keeping the total amount of diabatic heating fixed. We focus on characteristics of the response which would be particularly important if the circulation interacted with the hydrologic and energy cycles: the overturning circulation and the low-level wind. In the limit of very small scale in either the longitudinal or latitudinal direction, the intensity of the overturning circulation tends towards the value for which the vertical energy transport balances the diabatic heating, which is also the limit in the non-rotating case (with β = 0). In the same limit, the low-level westerly jet still extends eastward of the center of diabatic heating, while there is no jet in the non-rotating case. The intensity of the overturning circulation decreases with increasing longitudinal or latitudinal scale of the diabatic heating. The low-level westerly jet decreases in maximum velocity and spatial extent relative to the spatial extent of the diabatic heating with increasing longitudinal or latitudinal scale of the diabatic heating, and the associated low-level eastward mass transport decreases with increasing longitudinal scale. Our results suggest that moisture-convergence feedbacks will favor small-scale convective disturbances while surface-heat-flux feedbacks would favor small-scale disturbances in mean westerlies and large-scale disturbances in mean easterlies.