کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1773653 1021142 2012 15 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
General circulation and transport in Saturn’s upper troposphere and stratosphere
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات علوم فضا و نجوم
پیش نمایش صفحه اول مقاله
General circulation and transport in Saturn’s upper troposphere and stratosphere
چکیده انگلیسی

We present a model for the general circulation and 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 Composite Infrared Spectrometer (CIRS) 0.1-mbar data but not the local maximum in 1-mbar temperatures, suggesting that it is capturing the phase of Saturn’s Semiannual Oscillation associated with a temperature minimum at the equator but not the opposite phase. The meridional circulation at low latitudes is found to be dominated by a seasonally reversing Hadley circulation, characterized by upwelling near the equator, cross-equatorial flow from summer to winter hemisphere, and strong subsidence centered near 25° latitude in the winter hemisphere. The cross-equatorial flow induces an asymmetry in which the equatorial jet is found to be stronger in the winter than in the summer stratosphere. The location of the subsidence near 25°N for Ls ∼ 310° coincides with local maxima in acetylene, diacetylene, and methylacetylene mixing ratios measured by Cassini/CIRS (Guerlet, S., Fouchet, T., Bézard, B., Moses, J.I., Fletcher, L.N., Simon-Miller, A.A., Flasar, F.M. [2010]. Icarus 209, 682–695). This result supports the suggestion by Guerlet et al. (2010) that the hydrocarbon abundances are enhanced at this latitude by pronounced downward transport of hydrocarbon-rich air from above. The lateral eddy diffusion coefficient is found to typically be ∼105–106 m2 s−1 at mid-latitudes, implying meridional eddy transport time scales of order 100–1000 years.


► We model the general circulation and dynamical transport in Saturn.
► The observed pole-to-pole temperature contrast is captured.
► A seasonally-reversing Hadley cell dominates meridional circulation at low latitudes.
► Subsidence predicted for 25N coincides with enhanced hydrocarbon abundances seen by Cassini/CIRS.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Icarus - Volume 218, Issue 2, April 2012, Pages 861–875
نویسندگان
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