**DPS Meeting, Madison, October 1998**

*Session 30. Jupiter I*

Contributed Oral Parallel Session, Wednesday, October 14, 1998, 2:00-3:20pm, Madison Ballroom D
[Previous] |
[Session 30] |
[Next]

## [30.07] Gravitational Signature of Jupiter's Deep Zonal Flows

*W.B. Hubbard (UAz)*

Groundbased and spacecraft-based measurements of Jupiter's
atmospheric motions show a pattern of zonal flows which
persists over decades. The flows alternate strongly with
latitude and show partial north-south symmetry. Peak zonal
cloud speeds with respect to the System III frame are about
100 m/s; Galileo Probe data at latitude 6.6 deg N show even
higher wind speeds at pressures up to 21 bars. If such zonal
flows persist to sufficiently high pressures and mass
densities, they can be detectable in Jupiter's external
gravity field.

I bound the effects of zonal flow on Jupiter's external
gravity by considering two extreme models. For the first
model, I assume that Jupiter's interior has constant
specific entropy, and is thus barotropic, such that the
planet rotates differentially on cylinders. In the second
model, I assume that zonal flows are confined to a very
shallow atmospheric region of negligible mass and thus have
no effect on the gravity. In both models, the mass
distribution is obtained from the solution to the
steady-state Euler equation ({\bf v}\cdot \nabla){\bf
v}+(\nabla P)/\rho-{\bf g}=0, where {\bf v} is the
fluid velocity vector due to System III rotation plus
differential flow (if any), P is the pressure, \rho is
the mass density, and {\bf g} is the gravity vector.

The difference in predicted gravity for the two models is
about 30 mgal at the equator, as measured by an orbiter at
an altitude of 1000 km. Gravity anomalies above the 10th
degree are almost entirely determined by the zonal flow
field, tend to be anticorrelated with eastward wind speeds,
and have an amplitude on the order of a milligal. The
maximum gravity anomalies should occur if the zonal flows
persist to a depth about 1000 km below the cloud layers
(corresponding to a pressure of about 10 kbar). Such gravity
anomalies would be readily detectable by a low Jupiter
orbiter equipped with Galileo-level orbit-tracking
technology.

[Previous] |
[Session 30] |
[Next]