The simple multi-scale asymptotic model, originally derived by Majda (2007), is used to capture this multi-scale structure, where mesoscale fluctuations are directly driven by mesoscale heating and synoptic-scale circulation is forced by mean heating and eddy transfer of momentum and temperature. The eddy transfer of momentum and temperature is interpreted as the upscale impact from mesoscale fluctuations to synoptic-scale circulation. In the first JAS paper by Yang and Majda (2017a), the two-dimensional version of the multi-scale model drives the synoptic-scale circulation, successfully reproduces key features of flow fields with a front-to-rear tilt and compares well with results from a cloud-resolving model. In the second JAS paper by Yang and Majda (2017b), the three-dimensional version of the multi-scale model is studied. Results show that upscale impact of mesoscale disturbances that propagate at tilt angles (1100 ~ 2500) induces negative lower-tropospheric potential temperature anomalies in the leading edge, providing favorable conditions for shallow convection in a moist environment, while the remaining tilt angle cases have opposite effects. Even in the presence of upright mean heating, the front-to-rear tilted synoptic-scale circulation can still be induced by eddy terms at tilt angles (1200 ~ 2400). In the case with fast propagating mesoscale heating, positive potential temperature anomalies are induced in the lower troposphere, suppressing convection in a moist environment. This simple model also reproduces convective momentum transport and CCKWs in agreement with results from a recent cloud-resolving simulation.
This study based on a simple multi-scale model also has several implications for physical interpretation and comprehensive numerical models. First, the explicit expressions for eddy flux divergences of momentum and temperature provide a way of assessment of upscale impact of mesoscale disturbances of tropical convection on tropical waves, which should be useful to improve convective parameterization of organized tropical convection in GCMs, especially the so-called convective momentum transport that are widely recognized and studied in the literature. Secondly, it can be used to model many other phenomenon such as westward-propagating 2-day waves within Madden-Julian Oscillation and easterly waves in the ITCZ, providing a simple multi-scale framework for theoretically explaining scale interactions of organized tropical convection and practically diagnosing them through momentum and heat budgets.