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, 44 (7), 3000-3008

The Great Cold Spot in Jupiter's Upper Atmosphere

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The Great Cold Spot in Jupiter's Upper Atmosphere

Tom S Stallard et al. Geophys Res Lett.

Abstract

Past observations and modeling of Jupiter's thermosphere have, due to their limited resolution, suggested that heat generated by the aurora near the poles results in a smooth thermal gradient away from these aurorae, indicating a quiescent and diffuse flow of energy within the subauroral thermosphere. Here we discuss Very Large Telescope-Cryogenic High-Resolution IR Echelle Spectrometer observations that reveal a small-scale localized cooling of ~200 K within the nonauroral thermosphere. Using Infrared Telescope Facility NSFCam images, this feature is revealed to be quasi-stable over at least a 15 year period, fixed in magnetic latitude and longitude. The size and shape of this "Great Cold Spot" vary significantly with time, strongly suggesting that it is produced by an aurorally generated weather system: the first direct evidence of a long-term thermospheric vortex in the solar system. We discuss the implications of this spot, comparing it with short-term temperature and density variations at Earth.

Keywords: Jupiter; aurora; infrared; ionosphere; thermosphere; vortex.

Figures

Figure 1
Figure 1
H3 + emission measured by the CRIRES on VLT. These observations were made on (a) 17 October and (b) 31 December 2012. Images of emission from the H3 + ν2 Q(1,0) line, top, have been scaled to highlight subauroral emission, as shown by the color bar, and clearly show a region of darkening in the ionosphere (highlighted with arrows). The H3 + emission from these images has been summed over the latitudinal region of the darkening (demarked within the images by horizontal dotted lines), to produce two plots of varying H3 + emission with system III longitude, bottom, one for 17 October and one for 31 December. Here the region of darkening can be clearly seen for both nights. We have calculated the mean temperature and column density, the two values displayed within each region, both inside the dark region (blue), and in the surrounding ionospheric regions (red). Using separate data, we have also calculated the mean equatorial emissions (dashed line), temperature, and column density for each night, measured within an hour of these observations (green).
Figure 2
Figure 2
A map of mean H3 + emission across the 5 year Connerney and Satoh H3 + Jupiter image database. A latitude/longitude orthographic projection is shown on the left and a polar projection on the right. All maps show the emission scaled against the peak auroral brightness at latitudes between 75°N and 75°S with a gamma stretch of 0.5, and the bottom maps show a narrow range of emission brightness, scaled to highlight the subauroral region, as shown by the color bar. We identify the ionospheric locations that magnetically map to the main auroral emission (solid line; 30 RJ and Io spot and tail (dashed‐line; 5.9 RJ) [Grodent et al., 2008], and to Amalthea (dotted line; 2.544 RJ) [Connerney et al., 1998]. Also shown are the jovigraphic longitude and latitude in 30° steps (grey dotted line).
Figure 3
Figure 3
A clipped region of the latitude/longitude map (30–80°N, 270–360°W), showing how emission from this region varies with time over the 1995–2000 period. Emission is scaled from the peak auroral brightness at latitudes between 75°N and 75°S with a gamma stretch of 0.5, to highlight the subauroral region, as shown in the color bar. Each frame has been smoothed by 2° of latitude and longitude, in order to improve the signal to noise ratio, and lines of 15° of latitude and longitude are shown (grey dotted line). Between 1995 and 1997, there are significant variations in this region, but no clear spot, and from 1998 onward a clear dark region occurs within each of these images, evolving in location and morphology.

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Cited by 2 PubMed Central articles

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