Title: The tropospheric response to tropical and subtropical zonally asymmetric torques
Abstract: Tropospheric winds can be altered by vertical transfers of momentum accomplished by both convection and orographically excited gravity waves. To improve understanding of the tropospheric response to such momentum transfers, we use a series of analytical and idealized numerical models to investigate the tropospheric response to a set of prescribed, zonally asymmetric torques in the tropical and subtropical upper troposphere. Prescribed westward tropical torques are shown to produce a pattern of tropical ascent that is well described by linear dynamics, with equatorial Kelvin-wave ascent occurring east of the torque and subsidence occurring west of the torque in off-equatorial Rossby gyres. The zonal mean linear response consists of poleward flow in the region of the torque that is part of a Hadley-like circulation; for subtropical torques this amounts to a ???downward control??? balance. Moist convection can amplify the vertical motion response by reducing the gross moist stability. Because this amplification occurs only in precipitating regions, much of the vertical motion response to a torque is confined within the basic state intertropical convergence zone (ITCZ), even when the torque is subtropical and remote from the ITCZ. The perturbation of eddy momentum fluxes is also an important part of the response to an imposed torque.