DYNAMICS OF TRITONS ATMOSPHERE

THE recent Voyager encounter established certain facts about Triton's atmosphere: the surface pressure is in the range 1.5-1.9 Pa (15-19 μbar)1; the surface temperature is 38±3K (ref. 2); molecular nitrogen is the dominant atmospheric constituent3; hazes and clouds are visible not only on the limb but also against the surface4; the wind in the southern hemisphere is to the northeast at low altitudes (as shown by streaks on the surface4) and to the west at high altitudes (as shown by geyser-like plume tails4). Triton rotates with a period of 5.877 days in a right-hand sense about the south pole, where the season now is late spring4. Here we argue that these features can be explained if Triton, like Mars5, has a global, well-structured atmosphere in equilibrium with surface frosts. The subliming frost cap produces a polar anticyclone at low altitudes, with northeastward winds of ∼5 m s-1 within the Ekman boundary layer. The temperature contrast between the cold frost-covered pole and the warm unfrosted equator produces westward winds at high altitudes. © 1990 Nature Publishing Group.