Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p13c1684f&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P13C-1684
Physics
[3346] Atmospheric Processes / Planetary Meteorology, [5704] Planetary Sciences: Fluid Planets / Atmospheres
Scientific paper
Cassini, Voyager, and ground-based observations have provided strong evidence that temperature and constituent distributions in the stratosphere of Saturn are controlled by a complex interaction between photochemical, radiative, and dynamical processes. Knowledge of the mass transport circulation is therefore indispensable for a full and correct interpretation of spatial maps of trace species concentrations. We present an advanced model of the dynamical transport in Saturn's upper troposphere and stratosphere and derive the effective advective circulation and eddy transport coefficients required for use in two-dimensional (latitude-altitude) photochemistry-transport models. A three-dimensional Outer-Planet General Circulation Model (OPGCM) is used to generate the transport data. We find that the OPGCM adequately captures the global-scale, pole-to-pole temperature contrast, but overestimates mid- and high-latitude temperatures in the summer hemisphere by ~5 K. In addition, the model reproduces the local temperature minimum seen at the equator in Cassini/CIRS 0.1-mbar data but not the local maximum in 1-mbar temperatures (Guerlet et al. 2009), suggesting that It is capturing the phase of Saturn's Semiannual Oscillation associated with a temperature minimum at the equator but is not producing the opposite phase. The model predicts that a region of significant downward transport occurs in the 0.1 to 1-mbar layer near ±25° latitude during winter but not summer. This result supports the suggestion by Guerlet et al. (2010) that the observed local maxima in acetylene, diacetylene, and methylacetylene mixing ratios centered at 25°N in the winter hemisphere may reflect a region of pronounced downward transport, whereas the local minima seen at summer mid-latitudes may be associated with relatively weak vertical transport. The lateral eddy diffusion coefficient Kyy is found to typically be ~10^5-10^6 m^2s^-1 at mid-latitudes but is much smaller in the core of the equatorial jet.
Friedson Andrew James
Moses Julianne I.
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