Idealized studies of the ITCZ and its multi-Level circulations

The increasing availability of in-situ observations and the increasing horizontal and vertical resolution of Reanalysis data sets have revealed new features in the general circulation. Two such features have been identified in the Intertropical Convergence Zone and its associated large-scale overturning: the shallow return flow and the mid-level inflow. The shallow return flow is a low-level flow out of the ITCZ that lies directly over the boundary layer inflow and is distinct from the upper-level outflow. Previous studies have shown that this circulation is a direct response to low-level temperature gradients when deep convection is absent. These circulations are studied in more detail with idealized simulations of the ITCZ in a tropical channel model. The mid-level inflow is found to be driven by mid-level convergence caused by stratiform convective processes and their associated heating maximum in the upper troposphere. When active, the shallow return flow and mid-level inflow make significant contributions to budgets of water and moist static energy in the ITCZ region. Nested simulations that allow for convection-resolving resolution in the ITCZ will be presented and contrasted with simulations that use cumulus parameterization.