The atmosphere of Saturn - an analysis of the Voyager radio occultation measurements

Abstract

• Unexpectedly complex influx of ring material found in Saturn's equatorial upper atmosphere, including organics, water and nanograins. • Ring influx leads to reduction in major ions (H + and H 3 +); heavier molecular ions dominate Saturn's low-altitude equatorial ionosphere. • Major molecular ions at low-altitude still uncertain, but are likely to include H 3 O + and HCO + , and the mean modeled ion mass is 11 Da.

The structure of Titan’s atmosphere from Cassini radio occultations

“…The signal was tracked all the way to the surface for S and X bands, while the Ka signal disappeared at about 10 km above the surface. The primary contribution to absorption is from pressure-induced absorption by N 2 (Ho et al, 1968;Borysow and Frommhold, 1986;Lindal et al, 1985). A more detailed analysis of atmospheric absorption on Titan at radio wavelengths will be given elsewhere.…”

“…It has been successfully used for many bodies in the solar system, including Jupiter and its satellites (Eshleman, 1975;Hinson et al, 1997), Saturn (Lindal et al, 1985), Uranus (Lindal et al, 1987), Neptune and Triton (Lindal, 1992), Mars (Cahoy et al, 2006), and Venus (Jenkins et al, 1994;Hinson and Jenkins, 1995). Prior to Cassini, the Voyager 1 spacecraft was occulted by Titan in 1979, early in Titan's northern spring (Lindal et al, 1983).…”

Saturn Atmospheric Structure and Dynamics

“…The knee was also seen in temperature profiles from Voyager radio occultations at 3°S and 74°S (Lindal et al, 1985). Fletcher et al (2007b) used Cassini CIRS data from 2004-2006, during southern mid-summer, to map the strength and pressure of the knee as a function of latitude ( Figure 7.11).…”

“…There is a well-defined tropopause at ~80 mbar, separating a strongly statically stable stratosphere with temperatures increasing with altitude, from a troposphere with temperatures increasing with depth. In the upper troposphere, the temperature gradient increases with depth down to approximately 400-500 mbar, where the gradient becomes nearly dry adiabatic (Lindal et al 1985;Fletcher et al 2007b). This transition to the adiabat likely indicates the radiative-convective boundary, with temperatures and dynamics at higher pressures determined primarily by convection, and the temperatures at lower pressures determined by solar heating and the solar driven circulation.…”

“…Beyond the first scale height above the water condensation level, the lapse rate is assumed to once again become dry adiabatic because the other condensate species release too little latent heat to have a significant effect. Above the 1 bar level dry adiabatic lapse rates have been retrieved from Voyager occultations (Lindal et al 1985) and Cassini CIRS , with a transition to a stable temperature gradient occurring at ~400-500 mbar.…”