Fig. 1: | Nature Communications

Fig. 1

From: A hexagon in Saturn’s northern stratosphere surrounding the emerging summertime polar vortex

Fig. 1

Brightness temperature maps of the north polar stratosphere from 2013 to 2017. Brightness temperatures were averaged over the 1280–1320 cm−1 range sensing 0.5–5.0 mbar, and each map has the same temperature scale. The figure indicates the hexagonal boundary to the polar stratospheric hood. The panels provide maps for a August 17, 2013, b October 18, 2014, c June 9, 2016, d September 20, 2016, e November 8, 2016, f February 12, 2017, g April 17, 2017 and h August 26, 2017. Maps with spectral resolutions of 2.5 cm−1 (REGMAPs) and 15.0 cm−1 (FIRMAPs) were used here, spanning Cassini’s solstice mission and proximal orbits. These data were obtained from a relatively high orbital inclination to facilitate views of the north pole. Spectra have been averaged on an equal-area projection to reduce noise. Regions of dark blue represent missing data and defects—in particular, the central polar cyclone was partially obscured in the final FIRMAP of the mission acquired in August 2017 (h). The hexagonal boundary near 78–80° latitude is clearest in the October 2014 (b), November 2016 (e) and February 2017 (f) data. The sinusoidal variation of temperature is shown in Fig. 2e–f for two dates