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Abstract In the study of subgrid-scale tropical convection, the importance of retaining the frequently omitted “nontraditional” component of the Coriolis force is increasingly being recognized. A number of recent papers have developed linear theories examining the behavior of a diabatic heat-source-driven convective circulation in the presence of the full Coriolis force, and it was shown that the nontraditional Coriolis terms drive vertical shears on the large scales through upscale fluxes of momentum. In the present work, we generalize these results to the nonlinear regime, using a formal asymptotic theory based upon the fact that rotation is a second-order effect compared with advection by the vertical component of velocity at subgrid scales. Ultimately, we demonstrate that the same basic flow structures persist, with a particular emphasis on the counterrotating vortex pair induced by the nontraditional Coriolis terms which drive a westward tilt in convection. We compute the form of the upscale momentum flux convergence in the nonlinear regime, greatly extending the regimes of validity provided by the simple analytical expressions previously given in the linear case. This study constitutes an important step toward being able to accurately and consistently parameterize the large-scale vertical shear driven by nonlinear, subgrid convective processes under the influence of the nontraditional Coriolis force terms.
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Balanced Convective Circulations in a Stratified Atmosphere. Part I: A Framework for Assessing Radiation, the Coriolis Force, and Drag
Abstract The so-called traditional approximation, wherein the component of the Coriolis force proportional to the cosine of latitude is ignored, is frequently made in order to simplify the equations of atmospheric circulation. For velocity fields whose vertical component is comparable to their horizontal component (such as convective circulations), and in the tropics where the sine of latitude vanishes, the traditional approximation is not justified. We introduce a framework for studying the effect of diabatic heating on circulations in the presence of both traditional and nontraditional terms in the Coriolis force. The framework is intended to describe steady convective circulations on anfplane in the presence of radiation and momentum damping. We derive a single elliptic equation for the horizontal velocity potential, which is a generalization of the weak temperature gradient (WTG) approximation. The elliptic operator depends on latitude, radiative damping, and momentum damping coefficients. We show how all other dynamical fields can be diagnosed from this velocity potential; the horizontal velocity induced by the Coriolis force has a particularly simple expression in terms of the velocity potential. Limiting examples occur at the equator, where only the nontraditional terms are present, at the poles, where only the traditional terms appear, and in the absence of radiative damping where the WTG approximation is recovered. We discuss how the framework will be used to construct dynamical, nonlinear convective models, in order to diagnose their consequent upscale momentum and temperature fluxes.
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- Award ID(s):
- 2224293
- PAR ID:
- 10479236
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of the Atmospheric Sciences
- Volume:
- 80
- Issue:
- 12
- ISSN:
- 0022-4928
- Format(s):
- Medium: X Size: p. 2915-2924
- Size(s):
- p. 2915-2924
- Sponsoring Org:
- National Science Foundation
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