Other
Scientific paper
Nov 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004dps....36.3013s&link_type=abstract
American Astronomical Society, DPS meeting #36, #30.13; Bulletin of the American Astronomical Society, Vol. 36, p.1135
Other
2
Scientific paper
Voyager observations showed that Saturn's equatorial jet blew eastward at 450 m/s in 1980-81. However, subsequent Earth observations between 1996-2002 showed the equatorial jet speed to be approximately 350 m/s (Sanchez-Lavega et al., 2003). Sanchez-Lavega et al. interpreted this difference to be a true slowdown, but uncertainties in cloud altitudes combined with Cassini CIRS observations of vertical wind shear raise questions about whether the difference represents a real slowdown or simply changes in the altitudes of the observed clouds. A major event that could have influenced the winds occurred in 1990, when a huge convective storm, called a Great White Spot (GWS), erupted in the equatorial region of Saturn (Sanchez-Lavega, 1994). Here, we test the hypothesis that a GWS-like convective event can cause a slowdown of Saturn's equatorial jet like that observed. Mechanisms for slowing the winds include (1) potential vorticity mixing caused by such a storm, which would transport eastward momentum to higher latitudes, (2) momentum transport away from the jet by storm-induced atmospheric waves and (3) direct vertical mixing with a hypothetical source of deep, slow-moving air. We present order-of-magnitude estimates and fully nonlinear numerical simulations of the atmospheric flow using the EPIC atmosphere model. We envision that GWS-like convective events transport moist air from the deep troposphere to the neutrally buoyant level near the tropopause. Accordingly, we added localized mass-pulses to the equatorial upper troposphere to represent the effects of a GWS in the EPIC model. Our estimates and preliminary simulations suggest that GWS-like events can only cause wind-speed variations exceeding 50 m/s when the storm mass is unrealistically large. To elucidate the dynamical mechanisms involved, we performed a range of simulations which showed that the background wind profiles and other parameters strongly influence the dynamical response to a GWS. We will summarize these simulations in our presentation. This study is supported by NSF grant AST-0206269.
Kursinski Robert E.
Sayanagi Kunio Max
Showman Adam P.
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