Thermal Emission From Saturn's Polar Cyclones. Issue 11 (5th June 2018)

• Record Type: Journal Article
• Authors: Achterberg, R. K.; Flasar, F. M.; Bjoraker, G. L.; Hesman, B. E.; Gorius, N. J. P.; Mamoutkine, A. A.; Fletcher, L. N.; Segura, M. E.; Edgington, S. G.; Brooks, S. M.
• Is Part Of: Geophysical research letters. Volume 45:Issue 11(2018)
• Page Start: 5312
• Page End: 5319
• Publication Date: 2018-06-05
• Subjects: Saturn -- Cassini -- temperatures; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2018GL078157
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We have used data from the Cassini Composite Infrared Spectrometer to map the temperatures in Saturn's polar cyclones at the highest spatial resolution obtained during the Cassini mission. We find temperature contrasts of 7 K in the upper troposphere within 1.4° of both poles, roughly 50 percent larger than earlier measurements at lower spatial resolution. The polar hot spots weaken with depth, disappearing near 500 mbar. In the stratosphere, the polar hot spot becomes broader, extending 4° from the poles, and weakens with altitude disappearing near 1 mbar. A thermal relaxation model shows that the tropospheric hot spot is consistent with adiabatic heating from subsidence with a vertical velocity of about −0.05 mm/s above 500 mbar. The observed temperature gradients imply that the winds in the polar cyclone decay with increasing altitude over roughly three pressure scale heights above the 200‐mbar level. Plain Language Summary: We have used data from the Composite Infrared Spectrometer to map the temperatures in Saturn's polar cyclones during the Cassini mission. The final orbits of the mission enabled the highest spatial resolution data (20 km) of the mission. The analysis of this data reveals temperature contrasts of 7 °C (11°F) in the upper troposphere within 1.4° of both poles which is roughly 50% larger than measurements taken at lower spatial resolution earlier in the mission. We find that the polar hot spot temperature contrast weakens with depth in the troposphere. It was discovered that the hot spot temperature contrast in the stratosphere is broader than seen in the troposphere and weakens with increased altitude. The tropospheric temperature contrasts can be explained by slowly descending vertical winds at a rate of 0.05 mm/s. We observed that the temperature gradients are consistent with rapidly decaying winds over increasing altitude at the tropopause. Key Points: Both poles have warm cyclonic vortices with 100‐mbar temperatures increasing by 7 K within 1.2 degrees of the pole Temperatures are consistent with subsidence of 0.05 mm/s at 100 mbar extending down to at least 500 mbar Temperature gradients imply that the cyclonic winds decay with altitude over three scale heights in the upper troposphere and stratosphere