Juno radio occultations reveal the structure of Jupiter's cold northern polar vortex

Context. Jupiter’s polar upper troposphere and stratosphere host a persistent cold vortex poleward of 65°N, but its detailed structure and dynamics have remained difficult to resolve. Aims. The goal is to characterize the thermal structure and dynamics of the polar vortex using new and complementary remote sensing techniques. Methods. We used a combination of high-resolution vertical profiles derived from Juno’s recent radio occultation measurements and mid-infrared imaging from the VLT/VISIR instrument. The former provided direct retrievals of temperature and density near and within the vortex, while VISIR imaging revealed spatial thermal contrasts across the region. Results. Our analysis confirms the presence of a steep meridional temperature jump at 65°N, of about 7±1 K at 100 mbar, which is consistent with a strong vertical wind shear and a prograde polar stratospheric jet reaching up to 80 ms−1 at the 10 mbar level. We find the atmosphere to be thermally stable above 0.55 bar, reaching a Brunt-Väisälä frequency of 0.025 s−1 in the mid-stratosphere. Thermal contrasts observed in the infrared data align with the vertical structures inferred from radio occultations, which validates the presence and extent of the cold vortex. Conclusions. These findings offer a quantitative analysis of the thermal structure and the dynamical behavior of Jupiter’s polar atmosphere and demonstrate the diagnostic power of combining radio occultation and thermal infrared techniques in planetary atmospheric studies.