Twenty years ago, Andy Majda and Rupert Klein developed a multiscale asymptotic theory of tropical dynamics which they named IPESD. IPESD is a linear, forced, dynamical theory on the tropical synoptic scales coupled to a linear, slower, weak temperature gradient theory on the tropical planetary scales. The two scales interact with one another through upscale fluxes of momentum and temperature (the Reynolds stresses) and downscale advection from the planetary scale (developed by B. and Majda as the IMMD theory in 2010). Majda and myself used these theories in the following years to develop a multiscale kinematic model of the Madden Julian oscillation. Criticisms of this theory have missed the essential fact that the mathematics of the asymptotic analysis are inexorable, and verified by observation - the forcing is stronger on small scales and weaker on large scales; that’s all that is really needed to derive IMMD. In our MJO models, we showed that, in order to capture the westerly wind burst structure of the MJO, it was sufficient to force the planetary scales with momentum fluxes (Reynolds stresses) from westward tilted convective structures on the synoptic scales. Left unanswered was the cause of the westward tilted convection, though westward tilts had been observed repeatedly in MJO observing campaigns. The non-traditional terms in the Coriolis force (NCT) seem to provide an excellent candidate for westward tilts, but it is well known that these terms are too weak on scales greater than the mesoscale to affect the dynamics. However, the multiscale theories provide a distinct route for the NCT to affect the planetary scales - through upscale fluxes of momentum. We will show analytically that the net-NCT affects tropical convection by generating zero force in the vertical direction, a westward velocity field in regions of upward flow, and a recirculation in regions of downward flow, around a convective structure. The upscale fluxes from these circulations drive the vertical/westward tilt that was necessary to generate the westerly wind burst in the Majda/Biello models of the MJO. We will also show how these results, westward tilt and the westerly wind burst, can be created in simple laboratory experiments. We sincerely hope that Andy would have been gratified by these results, and excited by our experiment.

There has been increasing realization that the non-traditional Coriolis force terms may have a significant effect on convective circulation and organization in the tropics. In this talk, we introduce the concept of the net Coriolis force of a fluid dynamical flow. In order to compute the net Coriolis force, we assume incompressible flow - and therefore incompressible net Corolis force. Through the Leray projection we are able to construct, both, the pressure needed to maintain an incompressible force, and the net Coriolis force, itself. We explore the effects of the net Coriolis force on basic flows by decomposing the velocity field using the Helmholtz decomposition, and we describe poloidal and horizontal flows separately. We then compute the net Coriolis force associated with the Traditional Corolis terms (proportional to the sine of latitude) and, separately, the net Non-Traditional Coriolis terms (proportional to the cosine of latitude). We show that all poloidal circulations - which are flows which lack a vertical component of vorticity - are in vertical gesotrophic balance. Therefore, the pressure induced by such flows is simply computed without the need to invert a Laplacian. Using the Dynamics of Non-rotating Updraft Tori (DoNUT), which is a polodial circulation framework introduced by Igel & Biello (2020) to describe the full kinematic circulation of atmospheric convection, we show that the net non-traditional Coriolis force has zero component in the vertical direction, is westward in the regions of upward flow, and recirculates eastward poleward of the upward flow. The resulting circulations lead to vertical/westward oriented momentum flux from the resulting Reynold’s stress terms. We will conclude by discussing implications of these circulations for tropical convective organization.