Temperature and Composition of Saturn's Polar Hot Spots and Hexagon

Abstract

Saturn's poles exhibit an unexpected symmetry in hot, cyclonic polar vortices, despite huge seasonal differences in solar flux. The cores of both vortices are depleted in phosphine gas, probably resulting from subsidence of air into the troposphere. The warm cores are present throughout the upper troposphere and stratosphere at both poles. The thermal structure associated with the marked hexagonal polar jet at 77 degrees N has been observed for the first time. Both the warm cyclonic belt at 79 degrees N and the cold anticyclonic zone at 75 degrees N exhibit the hexagonal structure.

Saturn Atmospheric Structure and Dynamics

“…Allison et al (1990) proposed that the hexagon is a stationary Rossby wave imbedded in and meridionally trapped by the eastward jet, and forced by the interaction of the jet with the NPS. Matching the observed phase velocity requires that the Rossby wave be vertically trapped, which may be consistent with the confinement of the observed hexagon to the troposphere (Fletcher et al 2008). …”

“…In addition to the large scale equator-to-pole temperature gradients, between ~2-300 mbar there are temperature variations of 2-3 K on the scale of the zonal jets. Outside the equatorial region, the temperature gradients are correlated with the mean zonal winds, with warmer temperatures where the winds are cyclonic, and colder temperatures where the winds are anticyclonic (Conrath and Pirraglia 1983;Fletcher et al 2007bFletcher et al , 2008. Temperatures in the equatorial region have been observed to oscillate with a period of ~15 Earth years (Orton et al 2008; section 7.3.7).…”

“…Prior to 2009, however, the hexagon was detected in thermal emission by both CIRS and VIMS. Maps of upper tropospheric temperatures (100 to 800 mbar) by CIRS (Fletcher et al 2008) show a hexagonal warm band at 79°N, and a hexagonal cold band at 76°N (Fig. 7.20 left).…”

“…7.22 right). Hurricanes are warm-core features; the Saturn south polar vortex has enhanced VIMS 5 μm emission at the pole, indicating clearing at depth, and anomalously warm central temperatures in CIRS data just beneath the tropopause (by 5 K) and also in the stratosphere (by 3-4 K) (Fletcher et al 2008). The warm central core implies a decay of the vortex wind speed with altitude of ~10 m s -1 per scale height (26 km at the pole), which is also consistent with the slightly stronger wind speeds measured by VIMS at deeper levels (Dyudina et al 2008b).…”

Weak Jets and Strong Cyclones: Shallow-Water Modeling of Giant Planet Polar Caps

“…This discovery was followed in 2007 by infrared imaging of both polar hemispheres by the NASA Cassini mission, currently in orbit around Saturn. A surprising result was that both poles exhibited very localized tropospheric hot spots, though in 2007 one pole was receiving constant summer sunlight and the other was not (Fletcher et al 2008). These hot spots were 6-8 K warmer than fluid that is just 108 from the pole.…”