Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p11b1272o&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P11B-1272
Physics
5709 Composition (1060), 5737 Magnetospheres (2756), 5744 Orbital And Rotational Dynamics (1221), 6207 Comparative Planetology, 6929 Ionospheric Physics (1240, 2400)
Scientific paper
Infrared observations of the polar regions of the outer planets have revealed similarities to the Earth's atmosphere and some new phenomena. The most dominant force which is apparent in time-dependent studies of the poles is seasonal radiative forcing, which was detected in Saturn's stratosphere as early as 1973. For Saturn, Uranus and Neptune, planets with substantial obliquities, the seasonally dependent changes are predictable and can be used to constrain abundances of optically active gases and the rate of restoration by stratospheric circulation. In the case of Neptune, recent evidence shows that the heating is sufficient to allow a "leak" from the reservoir of methane in the deep atmosphere into the polar stratosphere. New thermal images of Uranus show that the winter pole of Uranus which has only recently emerged fully from darkness is colder than when it was in the middle of winter when Voyager 2 visited, confirming the substantial seasonal phase delay associated with radiative heating and cooling models. Even Jupiter with its 3-degree obliquity shows clear evidence for seasonal forcing of temperatures in the upper troposphere and stratosphere. The second most prominent characteristic of the resolvable polar temperature fields in Jupiter and Saturn is the formation of polar vortices. Jupiter's polar vortices are cold, similar to those detected in the terrestrial planets; they have sharp equatorward boundaries which are characterized by Rossby waves which rotate at the speed of the local zonal wind flow and are coincident with the similarly irregular boundaries of a polar haze, also known as "polar hoods". The cold vortex at Saturn's northern winter pole is muted, but Saturn also has a unique "warm polar vortex" in the south (late summer) pole which shows no apparent wave structure. Saturn's warm polar vortex has no counterpart in the Earth's atmosphere, where summer radiative warming simply dissipates the cold winter vortex. Saturn also possesses dynamically driven hot regions within 2 degrees of its poles where dynamics is driving relatively dry air downwards, causing adiabatic warming and clearing the atmosphere; this phenomenon also has no terrestrial counterpart. Jupiter's upper polar stratosphere is warmed in discrete local regions by Joule heating from energetic particles cascading into the neutral atmosphere. The northern auroral-related polar "hot spot" has a very predictable geometry, but an amplitude that is variable over time scales of months. On the other hand, the stratosphere 25-30 degrees from Neptune's pole shows signs of ephemeral hot spots which are more likely to related to dynamics. These phenomena provide a rich basis of constraints for global climate models which must, at least for Jupiter, be coupled with models of auroral energy transport.
Encrenaz Th.
Fletcher Lauren
Greathouse Thomas
Leyrat Cedric
Orton Glenn
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