Summer outbursts in the coma of comet 67P/Churyumov–Gerasimenko as observed by Rosetta–VIRTIS

We present wind speeds at the ~ 1 bar level at both Jovian polar regions inferred from the 5-μminfrared images acquired by the Jupiter InfraRed Auroral Mapper (JIRAM) instrument on the NationalAeronautics and Space Administration Juno spacecraft during its fourth periapsis (2 February 2017). Weadopted the criterion of minimum mean absolute distortion (Gonzalez & Woods, 2008) to quantify themotion of cloud features between pairs of images. The associated random error on speed estimates is 12 m/sin the northern polar region and 9.8 m/s at the south. Assuming that polar cyclones described by Adriani et al.(2018, https://doi.org/10.1038/nature25491) are in rigid motion with respect to System III, tangentialspeeds in the interior of the vortices increase linearly with distance from the center. The annulus of maximumspeed for the main circumpolar cyclones is located at approximatively 1,000 km from their centers, withpeak cyclonic speeds typically between 80 and 110 m/s and ~50 m/s in at least two cases. Beyond theannulus of maximum speed, tangential speed decreases inversely with the distance from the center withinthe Southern Polar Cyclone and somewhat faster within the Northern Polar Cyclone. A few small areas ofanticyclonic motions are also identified within both polar regions