Temperature (K)

Figure 4.1. Equatorial temperature/pressure profiles of the giant planet atmospheres: Jupiter, solid line; Saturn, dotted line; Uranus, dashed line; Neptune. dot-dashed line.

the main ethane band at 12.2 ^m. If the stratosphere cools, this overlap rapidly disappears, effectively shutting off the cooling to space by ethane and acetylene. Hence the stratospheric temperatures of the giant planets would appear to be almost "thermostatted" by the presence of these molecules.

At even higher altitudes, significant ionization (and thus heating) of the atmosphere is allowed via solar extreme-ultraviolet (EUV) photons and bombardment with charged particles from the solar wind and cosmic rays. The breaking of gravity waves propagating vertically from the troposphere may also be important. A description of the ionospheres of the outer planets is beyond the scope of this book, but is well described by Atreya (1986).

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