The effects of moist convection on the tropospheric response to tropical and subtropical zonally-asymmetric torques

Tropospheric winds can be altered by vertical transfers of momentum caused by orographic gravity waves and convection, both of which tend to be highly localized in space. We showed in separate work that such zonally-asymmetric torques produce a characteristic response in dry models, with a pattern of tropical ascent that is qualitatively well-described by linear dynamics and a meridional shift of the eddy-driven mid-latitude jet. Here we use several idealized models to examine the effects of moisture on the tropospheric response to zonally-asymmetric torques. While the dynamical response to an upper-tropospheric toque in moist models can have a spatial structure that is qualitatively similar to that in dry models, moisture introduces several important modifications. One of the most dramatic of these is an amplification of the vertical velocity by nearly an order of magnitude in moist models. This occurs in a general circulation model with parameterized moist convection and an entirely oceanic lower boundary, and also in a quasi-linear model of the troposphere's first-baroclinic mode. The amplification is shown to result from the reduced effective static stability of a moist atmosphere, and can thus be rectified by the distribution of precipitation in the basic state. Given this amplification of the irrotational part of the response, we show how the vorticity budget necessitates changes in the horizontal structure of the nondivergent flow. The intensity and horizontal structure of the response in moist models can also be greatly altered by wind-induced surface heat exchange (WISHE), with enhanced zonal winds increasing ocean evaporation and convectively-coupled ascent. We briefly discuss some possible implications of these results for the effect of vertical momentum transfers on regional precipitation.