Vertically resolved weak temperature gradient analysis of the Madden‐Julian Oscillation in SP‐CESM

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Abstract

Abstract The collective effects of convection can influence large‐scale circulations that, in turn, act to organize convective activity. Such scale interactions may play an important role in moisture‐convection feedbacks thought to be important to both convective aggregation and the Madden‐Julian Oscillation, yet such interactions are not fully understood. New diagnostics based on tropical weak temperature gradient (WTG) theory have begun to make this problem more tractable, and are leveraged in this study to analyze the relationship between various apparent heating processes and large‐scale vertical moisture advection in SP‐CESM. WTG theory provides a framework for accurately diagnosing intraseasonal variations in large‐scale vertical motion from apparent heating, allowing large‐scale vertical moisture advection to be decomposed into contributions from microphysical processes, subgrid scale eddy fluxes, and radiative heating. This approach is consistent with the column moist static energy (MSE) budget approach, and has the added benefit of allowing the vertical advection term of the column MSE budget to be quantitatively partitioned into contributions from the aforementioned apparent heating processes. This decomposition is used to show that the MJO is an instability strongly supported by radiative feedbacks and damped by horizontal advection, consistent with the findings of previous studies. Periods of low, moderate, and high MJO amplitude are compared, and it is shown that changes in the vertical structure of apparent heating do not play a dominant role in limiting the amplitude of the MJO in SP‐CESM. Finally, a diagnostic approach to scale analysis of tropical dynamics is used to investigate how the governing dynamics of various phenomena differ throughout wavenumber‐frequency space. Findings support previous studies that suggest the governing dynamics of the MJO differ from those of strongly divergent convectively coupled equatorial waves.

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