The atmosphere of Jupiter has a complex circulation which, until recently, has been observable only at the cloud tops(1,2); the mechanisms driving the winds, and the nature of the interior circulation, remained unknown(3). Recent analyses(4-6) of the radio signal from the Galileo probe, obtained during its descent into the jovian atmosphere, have suggested a vigorous interior circulation below the 4-bar level. Here we report an independent measurement of the winds below the cloud tops, making use of the data obtained by the two accelerometers on the descending probe. We find evidence for two distinct wind regimes, in general agreement with the Doppler radio measurements : a region of wind shear between 1 and 4 bar, where the wind speed increases dramatically with depth; and then a region of constant high-velocity winds down to at least the 17-bar level.