Evolution of the Horizontal Winds in Jupiter's Great Red Spot From One Jovian Year of HST/WFC3 Maps

Abstract

The Great Red Spot is an enduring large anticyclone in Jupiter's atmosphere, situated in the South Tropical Zone (Figure 1). Anticyclonic flow in this zone is perturbed over the northern edge of the GRS so that it locally protrudes into the typically dark and reddish South Equatorial Belt (SEB) to the north. The SEB features dramatic global-scale changes in coloration, cloud properties, and convective activity (e.g., Fletcher et al., 2011Fletcher et al., , 2017Rogers, 1995;Sánchez-Lavega & Gómez, 1996), but the most notable change in the GRS itself is more monotonic in nature: a continuous decrease in size over more than 100 years of accurate observations (Simon et al., 2018).The size and longevity of the GRS make it unique among outer solar system vortices, yet it also serves as an archetype of a class of "pancake vortices"-anticyclones embedded in stably stratified fluids-also including vortices like the dark spots on Neptune and salt lens eddies in the Earth's oceans (e.g., Dowling, 1995;Hassanzadeh et al., 2012;Yim et al., 2016). Pancake vortices have a thickness much smaller than their horizontal dimensions, like the GRS whose horizontal scale is some 50 times greater than vertical scale, according to theoretical arguments based on laboratory experiments and Jovian vortex velocity fields (Lemasquerier et al., 2020). Terrestrial ocean eddies transport heat meridionally by both stirring (turbulent) and trapping (bulk transport) mechanisms (Sun et al., 2018). Trapping is limited on Jupiter because major vortices are bounded by jets that limit meridional migration, although trapping could be significant on Saturn, where poleward migration of the anticyclone created by the 2010 Great White Storm was observed

The depth of Jupiter’s Great Red Spot constrained by Juno gravity overflights

“…The shape of the GRS has evolved over the past several decades, with its longitudinal dimension shrinking and giving the vortex a more circular shape (18,19). We measured horizontal wind speeds in the GRS using optical data acquired about 25 days prior to PJ21 (17,20), taken as part of an annual Hubble Space Telescope observing program (21). Mean velocities measured in the high-speed ring are 106 m First release: 28 October 2021 science.org (Page numbers not final at time of first release) 3…”

“…The GRS velocity field (black arrows) at the time of PJ21 ( 20 , 32 ) with Juno tracks during PJ18 and PJ21 (gradient lines) is superimposed on JunoCam imaging of the GRS during PJ21 ( 33 ). The spacecraft altitude during the GRS closest approach (latitude 20°S) was 13,000 km during PJ18 and 19,000 km during PJ21, with eastward longitudinal offsets of 11° and 2°, respectively.…”

“…( A ) Density anomalies as a function of depth and latitude, for a transversal section taken at the longitude passing through the GRS center at the time of the velocity measurements ( 17 , 20 , 32 ). ( B ) Surface gravity anomalies as a function of longitude and latitude.…”

Kronoseismology. VI. Reading the Recent History of Saturn’s Gravity Field in Its Rings

“…We can also note that the variations in both the amplitudes and pattern speeds of these gravitational anomalies provide yet another means of better constraining their origins. On Jupiter, both the sizes and drift rates of long-lived storms like the Great Red Spot have been observed to change over timescales of years to decades (Simon et al 2018;Barrado-Izagirre et al 2021;Wong et al 2021;Morales-Juberías et al 2022), and the variations in these storms' drift rates around the planet are even comparable to those found in Saturn's gravitational anomalies. Detailed examinations of the evolution of the structures in Saturn's atmosphere over the course of the Cassini Mission and beyond could therefore potentially reveal features with histories that match some of the signals identified in this work.…”

Temporal Variations in Vertical Cloud Structure of Jupiter's Great Red Spot, Its Surroundings and Oval BA From HST/WFC3 Imaging

“…During its long lifetime, the GRS has undergone size, shape and color changes. Its size has decreased by half over the past 130 years, with its shape becoming more circular, and it was recently shown to be darkening (Rogers, 1995; Simon et al., 2018; Wong et al., 2021). Changes in the UV and methane band reflectivities have also been measured, implying a change in the vertical distribution of the clouds and hazes (Simon et al., 2018).…”