Abstract
Thermal-IR imaging from space-borne and ground-based observatories
was used to investigate the temperature, composition and aerosol structure
of Jupiter’s Great Red Spot (GRS) and its temporal variability between
1995-2008. An elliptical warm core, extending over 8◦ of longitude and 3◦ of
latitude, was observed within the cold anticyclonic vortex at 21◦S. The warm
airmass is colocated with the deepest red coloration of the GRS interior. The
maximum contrast between the core and the coldest regions of the GRS was
3.0-3.5 K in the north-south direction at 400 mbar atmospheric pressure,
although the warmer temperatures are present throughout the 150-500 mbar
range. The resulting thermal gradients cause counter-rotating flow in the
GRS center to decay with altitude into the lower stratosphere. The elliptical
warm airmass was too small to be observed in IRTF imaging prior to 2006,
but was present throughout the 2006-2008 period in VLT, Subaru and Gemini
imaging.
Spatially-resolved maps of mid-IR tropospheric aerosol opacity revealed
a well-defined lane of depleted aerosols around the GRS periphery, and a
correlation with visibly-dark Jovian clouds and bright 4.8-µm emission. Ammonia
showed a similar but broader ring of depletion encircling the GRS.
This narrow lane of subsidence keeps red aerosols physically separate from
white aerosols external to the GRS. The visibility of the 4.8-µm bright periphery
varies with the mid-IR aerosol opacity of the upper troposphere.
Compositional maps of ammonia, phosphine and para-H2 within the GRS
interior all exhibit north-south asymmetries, with evidence for higher concentrations
north of the warm central core and the strongest depletions in
a symmetric arc near the southern periphery. Small-scale enhancements in
temperature, NH3 and aerosol opacity associated with localized convection
are observed within the generally-warm and aerosol-free South Equatorial
Belt (SEB) northwest of the GRS. The extent of 4.8-µm emission from the
SEB varied as a part of the 2007 ‘global upheaval,’ though changes during
this period were restricted to pressures greater than 500 mbar. Finally, a
region of enhanced temperatures extended southwest of the GRS during the
survey, restricted to the 100-400 mbar range and with no counterpart in visible
imaging or compositional mapping. The warm airmass was perturbed
by frequent encounters with the cold airmass of Oval BA, but no internal
thermal or compositional effects were noted in either vortex during the close
encounters.
AbstractThermal-IR imaging from space-borne and ground-based observatorieswas used to investigate the temperature, composition and aerosol structureof Jupiter’s Great Red Spot (GRS) and its temporal variability between1995-2008. An elliptical warm core, extending over 8◦ of longitude and 3◦ oflatitude, was observed within the cold anticyclonic vortex at 21◦S. The warmairmass is colocated with the deepest red coloration of the GRS interior. Themaximum contrast between the core and the coldest regions of the GRS was3.0-3.5 K in the north-south direction at 400 mbar atmospheric pressure,although the warmer temperatures are present throughout the 150-500 mbarrange. The resulting thermal gradients cause counter-rotating flow in theGRS center to decay with altitude into the lower stratosphere. The ellipticalwarm airmass was too small to be observed in IRTF imaging prior to 2006,but was present throughout the 2006-2008 period in VLT, Subaru and Geminiimaging.Spatially-resolved maps of mid-IR tropospheric aerosol opacity revealeda well-defined lane of depleted aerosols around the GRS periphery, and acorrelation with visibly-dark Jovian clouds and bright 4.8-µm emission. Ammoniashowed a similar but broader ring of depletion encircling the GRS.This narrow lane of subsidence keeps red aerosols physically separate fromwhite aerosols external to the GRS. The visibility of the 4.8-µm bright peripheryvaries with the mid-IR aerosol opacity of the upper troposphere.Compositional maps of ammonia, phosphine and para-H2 within the GRSinterior all exhibit north-south asymmetries, with evidence for higher concentrationsnorth of the warm central core and the strongest depletions ina symmetric arc near the southern periphery. Small-scale enhancements intemperature, NH3 and aerosol opacity associated with localized convectionare observed within the generally-warm and aerosol-free South EquatorialBelt (SEB) northwest of the GRS. The extent of 4.8-µm emission from theSEB varied as a part of the 2007 ‘global upheaval,’ though changes duringthis period were restricted to pressures greater than 500 mbar. Finally, aregion of enhanced temperatures extended southwest of the GRS during thesurvey, restricted to the 100-400 mbar range and with no counterpart in visibleimaging or compositional mapping. The warm airmass was perturbedby frequent encounters with the cold airmass of Oval BA, but no internalthermal or compositional effects were noted in either vortex during the closeencounters.
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