Influence of upper‐tropospheric inertial stability on the convective transport of momentum

This study verifies the apparent high positive correlation between environmental and convection‐relative inertial stability, and the transport of momentum by deep convection. We evaluate the hypothesis that convection structurally aligns itself to best access the region of lowest upper‐tropospheric inertial stability, while forming the lowest convective updraught‐relative inertial stability. A numerical experiment evaluates variations in the structure, behaviour and momentum‐transport characteristics of deep convection across the tropical‐plume genesis region in the eastern Pacific. This unique region forms as a precursor to tropical‐plume genesis, and possesses spatially varying very‐low upper‐tropospheric inertial stability (the potential vorticity locally reaches zero, or becomes slightly negative, in the northern hemisphere). Our results show that the vertical transport of horizontal momentum is predictable, given knowledge of the inertial‐stability fields immediately surrounding the convection. It is conjectured that the preferred mode of convective organization (squall‐line dominated versus more three‐dimensional) near the intertropical convergence zone is a function of the ambient inertial stability. Therefore, as the convection organizes itself, it selects the most efficient access to regions of lowest inertial stability to enable its upper‐tropospheric outflow. Copyright © 2003 Royal Meteorological Society