Saturn’s North Polar Storms in 2019 and 2020

Between March and October 2018 there was an outbreak of convective storms in Saturn between planetographic latitudes 66°N and 75°N, that grew sequentially in time, interacting with each other, expanding zonally, and disturbing the whole region between both parallel circles (Sánchez-Lavega et al., 2020). We present a study of the evolution of the dynamical activity in this region throughout 2019 (from February 27 to November 28) and 2020 (from February 23 to August 9) based on images taken with a network of ground-based telescopes and in two OPAL observing campaigns with the Hubble Space Telescope (Simon et al., 2015) on June 19-20, 2019 and July 4-5, 2020. The images show the presence of discrete spots mainly concentrated in two latitude ranges, between 60°N and 64°N and between 74°N and 77°N. In the 63°N we have studied the motion and activity of the system formed by three coupled vortices (Anticyclone-Cyclone-Anticyclone ACA, del Río-Gaztelurrutia et al., 2018). At higher latitudes, discrete white spot activity was continuous throughout the study period. The most notorious case was the unexpected development of a new bright storm at latitude 74.6°N ± 1° similar to those of 2018, detected for the first time on March 25, 2020 that moved westward with a zonal velocity of -8 m/s in System III. It reached a size of about 5,000 km but expanded rapidly eastward, forming a tail of white clouds that reached a length of about 33,000 km on the equatorial side of the hexagon wave. Other discrete bright spots were observed in April and May at 77°N with origin probably linked to the first storm. We have studied in detail the motion of the six vertices of the hexagonal wave to see if they have been affected by the development of these storms, taking as a reference the measured motion in previous years (Hueso et al., 2020). We present numerical simulations of the dynamics of this storm based on the Shallow Water model (García-Melendo and Sánchez-Lavega, 2017) and we compare it with the storms in 2018.

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