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Abstract Previous observational and modeling studies have suggested that moisture plays a dominant role in Madden–Julian oscillation (MJO) evolution. Using a realistic MJO simulation by incorporating the role of mesoscale stratiform heating in the Zhang–McFarlane deep convection scheme in the National Center for Atmospheric Research Community Atmosphere Model, version 5.3 (NCAR CAM5.3), this study investigates the factors responsible for the improved MJO simulation by examining moisture variations during different MJO phases. The results of column moist static energy (MSE) and moisture budgets show that during the suppressed phases of MJO, vertical advection acts to increase MSE anomalies for the development of deep convection while radiative heating and surface heat flux decrease MSE. The opposite holds true at the MJO mature phase. However, their roles largely cancel each other, leaving horizontal advection to play a major role in the low-level MSE increase during the suppressed phase of the MJO and MSE decrease after the MJO mature phase. A further analysis combining moisture and temperature budget equations is performed to demonstrate the effects of vertical advection and cloud processes within the column at each level. The vertical profiles of column-confined moisture tendency show that large-scale vertical advection induced by latent heat release and evaporation within shallow convective clouds is also important to the lower-tropospheric moistening during suppressed phases. This confirms the role of shallow convection in low-level moistening ahead of MJO deep convection. Radiative heating is vital across all MJO phases, and its warming effects keep the column humidity anomaly maintained in mature phases. None of these features are reproduced by the standard CAM5.3.
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Evaluating the Conservation of Energy Variables in Simulations of Deep Moist Convection
Abstract It is often assumed in parcel theory calculations, numerical models, and cumulus parameterizations that moist static energy (MSE) is adiabatically conserved. However, the adiabatic conservation of MSE is only approximate because of the assumption of hydrostatic balance. Two alternative variables are evaluated here: MSE − IB and MSE + KE, wherein IB is the path integral of buoyancy (B) and KE is kinetic energy. Both of these variables relax the hydrostatic assumption and are more precisely conserved than MSE. This article quantifies the errors that result from assuming that the aforementioned variables are conserved in large-eddy simulations (LES) of both disorganized and organized deep convection. Results show that both MSE − IB and MSE + KE better predict quantities along trajectories than MSE alone. MSE − IB is better conserved in isolated deep convection, whereas MSE − IB and MSE + KE perform comparably in squall-line simulations. These results are explained by differences between the pressure perturbation behavior of squall lines and isolated convection. Errors in updraftBdiagnoses are universally minimized when MSE − IB is assumed to be adiabatically conserved, but only when moisture dependencies of heat capacity and temperature dependency of latent heating are accounted for. When less accurate latent heat and heat capacity formulae were used, MSE − IB yielded poorerBpredictions than MSE due to compensating errors. Our results suggest that various applications would benefit from using either MSE − IB or MSE + KE instead of MSE with properly formulated heat capacities and latent heats.
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- Award ID(s):
- 1648681
- PAR ID:
- 10405562
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of the Atmospheric Sciences
- Volume:
- 78
- Issue:
- 10
- ISSN:
- 0022-4928
- Format(s):
- Medium: X Size: p. 3229-3246
- Size(s):
- p. 3229-3246
- Sponsoring Org:
- National Science Foundation
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