Saturn’s seasonal variability from four decades of ground-based mid-infrared observations

A multi-decade record of ground-based mid-infrared (7-25 $\mu$m) images Saturn is used to explore seasonal and non-seasonal variability in thermal emission over more than a Saturnian year (1984-2022). Thermal measured by 3-m 8-m-class observatories compares favourably with synthetic based on both Cassini-derived temperature records the predictions radiative climate models. 8-m class facilities are capable resolving contrasts scale Saturn's belts, zones, polar hexagon, cyclones, superimposed onto large-scale asymmetries. Seasonal changes brightness temperatures $\sim30$ K stratosphere $\sim10$ upper troposphere observed, as northern southern stratospheric vortices (NPSV SPSV) form spring dissipate autumn. The timings first appearance warm successfully reproduced models, confirming them be phenomena, albeit entrained within sharp boundaries influenced dynamics. Axisymmetric bands (4-5 per hemisphere) display gradients that strongly correlated zonal winds, indicating winds decay strength altitude, implying meridional circulation cells forming system cool zones belts. structure largely repeatable from (via comparison infrared 1989 2018), exception low-latitudes. Here we find evidence inter-annual variations because equatorial banding at 7.9 $\mu$m inconsistent $\sim15$-year period for oscillation, i.e., it not strictly semi-annual. Finally, observations between 2017-2022 extend legacy Cassini mission, revealing continued warming NPSV during summer. [Abr.]