The hypothesis we wish to prove is that deep ITCZ convection preferentially aligns its internal organization and momentum transport to take advantage of low inertial stability in the upper troposphere relative to the convection. Furthermore, we propose that a population of deep convective clouds should evolve toward a population of convective systems possessing the momentum transport into the upper troposphere which most efficiently used the low inertial stability by minimizing the resistance to upscale growth and development. In this way, the vertical structure of cumulus momentum transport is viewed as being dictated by upper tropospheric inertial stability moreso perhaps than by vertical winds shear.
To prove this hypothesis, an experiment is performed to resolve convective organization along the Pacific ITCZ during a tropical plume event, using the nonhydrostatic mesoscale model (UW-NMS) of Tripoli (1992). Through the use of multi-grid nesting, we are able to explicitly resolve cloud scales and convective transports to 1 km resolution. Simulations extend from pre-plume (undisturbed) conditions through to plume genesis (when inertial stability across the ITCZ lower appreciably; Mecikalski and Tripoli [1998]). Results suggest that indeed, convective momentum transports, for deep convection in the plume genesis region, occur in such a way as to maximize the low inertial stability of the environment. Easterly (down-gradient) momentum transports are found to occur in convection nearest the plume's base (as determined from satellite data); sensitivity tests suggest that an easterly momentum transport produces a "potential" inertial instability poleward of convection, favoring upper tropospheric flow into a tropical plume. In contrast, convection located farther away from the tropical plume's base tends to transport westerly momentum to cloud top, producing very low inertial stability on their equatorward flank (and upper-tropospheric convective outflow not entering a tropical plume).
These initial results back up the authors' claim that westerly, upgradient momentum transports along the ITCZ are more favored in non-plume conditions while easterly, downgradient momentum transports are more inclined to occur in the vicinity of tropical plumes. Further conjecture suggest then that the organization assumed by deep tropical convection (e.g., MCS vs. squall line) in general may be a strong function of the environmental (upper tropospheric) inertial stability