Kaspi, Yohai and Flierl, Glenn R. and Showman, Adam P. (2009) The deep wind structure of the giant planets: Results from an anelastic general circulation model. Icarus, 202 (2). pp. 525-542. ISSN 0019-1035 http://resolver.caltech.edu/CaltechAUTHORS:20090808-142502728
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The giant gas planets have hot convective interiors, and therefore a common assumption is that these deep atmospheres are close to a barotropic state. Here we show using a new anelastic general circulation model that baroclinic vorticity contributions are not negligible, and drive the system away from an isentropic and therefore barotropic state. The motion is still aligned with the direction of the axis of rotation as in a barotropic rotating fluid, but the wind structure has a vertical shear with stronger winds in the atmosphere than in the interior. This shear is associated with baroclinic compressibility effects. Most previous convection models of giant planets have used the Boussinesq approximation, which assumes the density is constant in depth; however, Jupiter's actual density varies by four orders of magnitude through its deep molecular envelope. We therefore developed a new general circulation model (based on the MITgcm) that is anelastic and thereby incorporates this density variation. The model's geometry is a full 3D sphere down to a small inner core. It is nonhydrostatic, uses an equation of state suitable for hydrogen–helium mixtures (SCVH), and is driven by an internal heating profile. We demonstrate the effect of compressibility by comparing anelastic and Boussinesq cases. The simulations develop a mean state that is geostrophic and hydrostatic including the often neglected, but significant, vertical Coriolis contribution. This leads to modification of the standard thermal wind relation for a deep compressible atmosphere. The interior flow organizes in large cyclonically rotating columnar eddies parallel to the rotation axis, which drive upgradient angular momentum eddy fluxes, generating the observed equatorial superrotation. Heat fluxes align with the axis of rotation, and provide a mechanism for the transport of heat poleward, which can cause the observed flat meridional emission. We address the issue of over-forcing which is common in such convection models and analyze the dependence of our results on this; showing that the vertical wind structure is not very sensitive to the Rayleigh number. We also study the effect of rotation, showing how the transition from a rapidly to a slowly rotating system affects the dynamics.
|Additional Information:||Copyright © 2009 Elsevier. Received 3 November 2008; revised 24 February 2009; accepted 8 March 2009. Available online 25 March 2009. This work has been supported by NSF grant AST-0708106, funds from the Woods Hole Oceanographic Institution academic program and the NOAA Climate and Global Change Postdoctoral Fellowship Program administrated by the University Corporation for Atmospheric Research. We are grateful to Jean-Michel Campin for his assistance in building the anelastic model. We thank Alan Plumb, Joe Pedlosky, Richard Lindzen, Sara Seager and Tapio Schneider for their comments and suggestions during the preparation of this work, and two anonymous reviewers for their insightful and constructive comments.|
|Subject Keywords:||Jovian planets; Jupiter, atmosphere; Jupiter, interior|
|Official Citation:||Yohai Kaspi, Glenn R. Flierl, Adam P. Showman, The deep wind structure of the giant planets: Results from an anelastic general circulation model, Icarus, Volume 202, Issue 2, August 2009, Pages 525-542, ISSN 0019-1035, DOI: 10.1016/j.icarus.2009.03.026. (http://www.sciencedirect.com/science/article/B6WGF-4VXDV16-1/2/436913881e50a6eaa7583464e72ec9f3)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||George Porter|
|Deposited On:||02 Sep 2009 23:36|
|Last Modified:||26 Dec 2012 11:10|
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