Numerical simulations of atmospheric dynamics on the giant planets

Details Numerical simulations of atmospheric dynamics on the giant planets Numerical simulations of atmospheric dynamics on the giant planets

Jun 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009phdt.........7l&link_type=abstract

Proquest Dissertations And Theses 2009. Section 0009, Part 0606 131 pages; [Ph.D. dissertation].United States -- Arizona: The U

Computer Science

Atmospheric Dynamics, Jupiter, Saturn, Moist Convection, Superrotation, Subrotation, Uranus, Neptune, Zonal Jets

Scientific paper

The giant planets exhibit banded zonal jet streams that have maintained their structures over decades. There are long-standing questions: how deep the wind structures extend? What mechanisms generate and maintain the observed winds? Why are the wind structures so stable? To answer these questions, we performed three-dimensional numerical simulations of the atmospheric flow using the primitive equations.
First, we use a simple Newtonian cooling scheme as a crude approach to generate atmospheric latitudinal temperature differences that could be caused by latent heating or radiation. Our Jupiter-like simulations show that shallow thermal forcing confined to pressures near the cloud tops can produce deep zonal winds from the tropopause all the way down to the bottom of the simulated atmosphere (a few hundred bars). These deep winds can attain speeds comparable to the zonal jet speeds within the shallow, forced layer; they are pumped by Coriolis acceleration acting on a deep meridional circulation driven by the shallow- layer eddies.
Next, we explicitly include the transport of water vapor and allow condensation and latent heating to occur whenever the water vapor is supersaturated. Our simulations show that large-scale moist convection associated with condensation of water vapor can produce multiple zonal jets similar to those on the gas giants (Jupiter and Saturn) and ice giants (Uranus and Neptune). For plausible water abundances (3-5 times solar on Jupiter/Saturn and 30 times solar on Uranus/Neptune), our simulations produce about 20 zonal jets for Jupiter and Saturn and 3 zonal jets on Uranus and Neptune. Moreover, these Jupiter/Saturn cases produce equatorial superrotation whereas the Uranus/Neptune cases produce equatorial subrotation, consistent with the observed equatorial jet direction on these planets. Sensitivity tests show that the water abundance is the controlling factor; modest water abundances favor equatorial superrotation, whereas large water abundances favor equatorial subrotation. This provides a possible mechanism for the existence of equatorial superrotation on Jupiter and Saturn and the lack of superrotation on Uranus and Neptune.

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