A conceptual spectral plume model for understanding tropical temperature profile and convective updraft velocities

Zhou, WY, Xie SP.  2019.  A conceptual spectral plume model for understanding tropical temperature profile and convective updraft velocities. Journal of the Atmospheric Sciences. 76:2801-2814.

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atmosphere, cape, climate change, cloud-ensemble, convection, cumulus parameterization, dynamics, entrainment, equilibrium, extreme events, instability, Meteorology & Atmospheric Sciences, part i, Radiative-convective, shallow, simulation, thunderstorms


The tropical tropospheric temperature is close to but typically cooler than that of the moist adiabat. The negative temperature deviation from the moist adiabat manifests a C-shape profile and is projected to increase and stretch upward under warming in both comprehensive climate models and idealized radiative-convective equilibrium (RCE) simulations. The increased temperature deviation corresponds to a larger convective available potential energy (CAPE) under warming. The extreme convective updraft velocity in RCE increases correspondingly but at a smaller fractional rate than that of CAPE. A conceptual model for the tropical temperature deviation and convective updraft velocities is formulated to understand these features. The model builds on the previous zero-buoyancy model but replaces the bulk zero-buoyancy plume by a spectrum of entraining plumes that have distinct entrainment rates and are positively buoyant until their levels of neutral buoyancy. Besides the negative temperature deviation and its increasing magnitude with warming, this allows the spectral plume model to further predict the C-shape profile as well as its upward stretch with warming. By representing extreme convective updrafts as weakly entraining plumes, the model is able to reproduce the smaller fractional increase in convective velocities with warming as compared to that of CAPE. The smaller fractional increase is mainly caused by the upward stretch in the temperature deviation profile with warming, which reduces the ratio between the integrated plume buoyancy and CAPE. The model thus provides a useful tool for understanding the tropical temperature profile and convective updraft velocities.