Because Jupiter is a large planet that rotates fast, the equatorial tangential velocity of the atmosphere is 12,7 km s-1, and decreases like the cosine of latitude. In the reference frame rotating with the planet the acceleration of gravity is 22,88 N kg-1 at the equator and 25 N kg-1 at the poles.
The structure of the upper atmosphere of Jupiter is reasonably well-known between 60 degrees north and south down to a pressure of 1 bar, thanks to the measurements of the Composite Infrared Spectrometer, during the swing-by of the Cassini spacecraft past Jupiter in late 2000 and early 2001 [RD.43]. In addition the equatorial atmosphere has been explored down to a pressure of 21 bars during the entry and descent of the Galileo probe [RD.44].
These measurements reveal that the structure of the atmosphere of Jupiter is relatively simple: a troposphere in convective equilibrium with a constant adiabatic lapse rate, topped by a well-defined tropopause at a minimum temperature of about 100 K above which the temperature increases to a temperature of 160 K and remains practically constant in the region of maximum deceleration and heat fluxes during entry. Above that constant temperature region, roughly above 300 km the temperature increases again.
The composition of the atmosphere of Jupiter has been measured by the Galileo probe between pressure levels of 0,51 bars and 21,1 bars [RD.44]. This composition is as follows (volume mixing ratio): H2 (86%), He (13,6%), CH4 (0,18%), N2 (0,07%). The above composition is valid for the troposphere and most of the stratosphere. The corresponding molar mass is 2,31x10-3 kg mol-1.
The atmosphere of Jupiter is subject to a small seasonal cycle and the equatorial stratosphere experiences cyclic temperature variations of about 10 K with a quasi-quadrennial cycle. This cycle seems to be related to wave activity [RD.45], and large-scale gravity waves have been observed by the Galileo Atmosphere Structure Instrument (ASI) during the Galileo entry [RD.46].