Driving of the subtropical jet by tropical convection

A moist, idealized model is used to examine the driving influence of deep tropical convection on the wintertime subtropical jet. The model is run with fixed zonally symmetric sea surface temperatures under perpetual solstice conditions. To focus on the strongest convective activity, the daily data is re-centered around the longitude of maximum tropical convection. The qualitative picture that emerges suggests that deep tropical convection in the summer hemisphere drives an anomalous localized Hadley cell that crosses into the winter hemisphere and drives a locally strengthened subtropical jet downstream via advection of planetary angular momentum. Momentum fluxes associated with both the divergent overturning circulation and rotational eddies drive a local longitudinal minimum of angular momentum where the localized Hadley cell crosses the equator, thus highlighting the complexity in interpreting the angular-momentum budget due to the inherent zonally asymmetric nature of tropical convection. The results are compared with the circulation in a dry model, where a single jet inside the Ferrel cell dominates the zonal mean flow. The role of moisture in driving a subtropical jet is discussed.