We report on a new series of CCD imaging obtained at Pic-du-Midi Obs. at red wavelengths (600-900 nm) of the longest-lived asymmetric feature in Saturn's atmosphere: the North Polar Spot (NPS).The observations covered a period of 1255 days spanning from May 1992 to November 1995. This completes our previous report on NPS data for the period 1990-1991 (Sanchez-Lavega et al., Science, 260, 329. 1993). Longitude measurements of NPS indicate an averaged longitudinal drift of -0.0296819 deg/(day) (relative to System III)for the whole 1990-1995 period, corresponding to a zonal velocity of +0.084 m/s. Combining the 1990-1995 data with the early 1980-1981 Voyager measurements of NPS indicates a steady angular acceleration of 2.8x10(-6) deg/(day)(-2) . Methane to continuum band filter photometry allowed us to determine the NPS absolute reflectivity, indicating that the NPS cloud tops are at pressure levels P < 90 mbar, well above the neighbouring clouds. A seasonal insolation model at latitude 75deg North that includes the extinction effect of a haze layer,together with a simple linear radiative response of the atmosphere to this external heating at different altitudes, suggest that the NPS life and motions are not dependent on the strong changes of the solar forcing. This work was supported in part by Universidad Pais Vasco project EA 050/95 and by the french Programme National de Planetologie.
AAS/Division for Planetary Sciences Meeting Abstracts #28
- Pub Date:
- September 1996