Despite direct solar EUV heating of Saturn’s upper atmosphere representing a minor energy source only, it is however important to note that solar EUV and shorter wavelength radiation is responsible for the majority of ionisation, and thus conductivity, outside of the narrow band of high latitude electron precipitation. This, in turn, may control thermospheric temperatures. As shown in Fig. 2, the region of magnetospheric electric field is considerably wider than the electron precipitation region, so the Joule heating region extends over a much wider region as well. Therefore, solar radiation does affect high latitude temperatures by means of its role as source of ionisation. This causes hemispheric differences in high latitude temperatures at solstice. In our solstice simulation (R19) we find exospheric temperatures averaged from 74°S to 90°S (the summer polar region) of 490 K, while averaging over the same latitude band in the northern (winter) hemisphere gives a value of 430 K. This difference of 60 K is a direct result of enhanced ionisation in the summer hemisphere, leading to stronger Joule heating there. We expect solar cycle variations of high latitude temperatures to lie within the same approximate range, stronger in the summer hemisphere than winter hemisphere, where solar ionisation is considerably weaker. The solar ionisation-induced hemispheric differences in atmospheric conductivity should similarly affect the magnetosphere, highlighting an interesting Sun–atmosphere–magnetosphere coupling chain that deserves more thorough examination in future studies.
the summer polar region
74°S to 90°S
°S
solstice simulation (R19)
exospheric temperatures
490 K
K
solstice simulation (R19)
exospheric temperatures
430 K
K
difference
60 K
K