HR: 0800h
AN: P11C-0133    [Abstracts]
TI: Effects of a Large Convective Storm on the Equatorial Jet of Saturn
AU: * Sayanagi, K M
EM: sayanagi@physics.arizona.edu
AF: Department of Physics, Lunar and Planetary Lab, University of Arizona, 1629 E University Blvd, Tucson, AZ 85721 United States
AU: Showman, A P
EM: showman@lpl.arizona.edu
AF: Department of Planetary Sciences, Lunar and Planetary Lab, University of Arizona, 1629 E University Blvd, Tucson, AZ 85721 United States
AB: Observations of Saturn between 1994-2004 revealed that the equatorial cloud-top wind blows at ~275~ms^-1, approximately half the speed of the Voyager-observed speed, ~470~ms^-1, in 1981. It has been hypothesized that the equatorial wind has been slowed by a large equatorial disturbance called the Great White Spot (GWS) in 1990. However, the fact that the clouds are estimated to be higher today than in the Voyager era makes it difficult to observationally isolate the vertical shear effects on the cloud-tracking speed measurements from a true wind speed change. We perform numerical simulations, using the Explicit Planetary Isentropic Coordinate (EPIC) model, to determine whether a GWS-like storm can decelerate the equatorial jet. Possible deceleration mechanisms the storm may trigger are potential vorticity (PV) homogenization, which accelerates the equatorial wind westward, and atmospheric waves transporting momentum away from the jet. Our simulations show that the storm does slow the equatorial wind in the stratosphere, but much less than what has been observed. When our model is initialized with no wind, the storm caused a westward acceleration of as much as 60~ms^-1. When initialized with the Voyager wind profile, the largest slowdown we obtain is ~30~ms^-1. This is consistent with our order of magnitude calculation, which shows that it is difficult for an atmospheric wave that could plausibly be generated by a GWS to change the tropospheric wind by the observed magnitude. Our result also implies that the storm's PV homogenization effect is weak. Our simulations hint that smaller scale effects such as gravity waves may contribute in slowing the equatorial wind although further study is necessary to estimate their strengths. We also present effects of the storm on the equatorial cloud morphology and compare our simulation results to observations of the GWS evolution.
DE: 3346 Planetary meteorology (5445, 5739)
DE: 5704 Atmospheres (0343, 1060)
SC: Planetary Sciences [P]
MN: Fall Meeting 2005