Seasonal Change on Saturn from 5 Years of Cassini/CIRS Observations

Details Seasonal Change on Saturn from 5 Years of Cassini/CIRS Observations Seasonal Change on Saturn from 5 Years of Cassini/CIRS Observations

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21430505f&link_type=abstract

American Astronomical Society, AAS Meeting #214, #305.05; Bulletin of the American Astronomical Society, Vol. 41, p.722

Astronomy and Astrophysics

Astronomy

Scientific paper

As Cassini completes its fifth year of orbital operations at Saturn, derivations of temperature and composition from the Composite Infrared Spectrometer (CIRS) are showing indications of seasonal change. Cassini arrived at Saturn shortly after winter solstice in the northern hemisphere, and will be present when Saturn goes through the spring equinox at the end of 2009. Thirty independent hemispherical mapping observations at 15.0 cm-1 resolution, comprising more than a million spectra, were binned with latitude for each date. Far-IR spectra (35-550 cm-1) were used to derive temperatures from 100-800 mbar and the para-hydrogen distribution (a tracer for vertical mixing) near 300 mbar. These were used as a priori for retrievals from mid-IR spectra (600-1450 cm-1) to update temperatures in the upper troposphere (75-250 mbar) and stratosphere (1-5 mbar), along with derivations of the distribution of mid-IR aerosol opacities and PH3 gas.
Stratospheric temperatures show the largest variability due to the short radiative timescales at higher altitudes, with cooling at southern mid-latitudes accompanied by a rapid warming at northern mid-latitudes. Equatorial and polar temperature changes are more complex, with dynamical perturbations due to Saturn's semi-annual oscillation at the equator (Orton et al., Nature, 453, 196-199) and atmospheric subsidence at the poles (Fletcher et al, 2008, Science, 319, 79-82). The warm southern stratospheric hood poleward of 70S shows signs of cooling, but high northern latitudes have yet to respond to the increased insolation. The north and south polar vortices, along with the northern hexagon, remained present in every CIRS observation. Tropospheric temperatures also show signs of variability. Super-equilibrium conditions of para-hydrogen (possibly indicative of more efficient aerosol catalysis) moved northwards from their location in 2005 (Fletcher et al., 2007, Icarus, 189, 457-478), consistent with Saturn's blue hues changing to the familiar ochre colours in the northern hemisphere as it becomes `hazier.'

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