Galileo probe measurements of the deep zonal winds of Jupiter

During the Galileo probe's descent into the upper atmosphere of Jupiter, data from the six science instruments on the probe were transmitted to the orbiter for 57.5 minutes. Accurate measurements of the probe's signal frequency, driven by an ultrastable oscillator (USO), enabled an accurate time history of the probe motions to be created. Removal from the frequency profile of known Doppler contributions, including the orbiter trajectory, the probe descent velocity, and the rotation of Jupiter, left a measurable frequency residual due to the horizontal and vertical winds of Jupiter, and probe spin and swing. Assumption of the dominance of the zonal horizontal winds allowed the frequency residuals to be inverted and resulted in the first in situ measurements of the deep zonal winds of Jupiter. It is found that beneath the cloud tops (about 5-700 mb) the winds are prograde, and rise rapidly to 170 m/s at 4 bars. Beyond 4 bars to the depth at which the link with the probe was lost, nearly 22 bars, the winds remain essentially constant and strong. When corrections for the effect of the adverse thermal environment on the probe USO frequency stability are included, the previously seen tendency for the zonal winds to increase at the deepest levels vanishes.