An enduring rapidly moving storm as a guide to Saturn’s Equatorial jet’s complex structure

Abstract

Saturn has an intense and broad eastward equatorial jet with a complex three-dimensional structure mixed with time variability. The equatorial region experiences strong seasonal insolation variations enhanced by ring shadowing, and three of the six known giant planetary-scale storms have developed in it. These factors make Saturn's equator a natural laboratory to test models of jets in giant planets. Here we report on a bright equatorial atmospheric feature imaged in 2015 that moved steadily at a high speed of 450 ms−1 not measured since 1980–1981 with other equatorial clouds moving within an ample range of velocities. Radiative transfer models show that these motions occur at three altitude levels within the upper haze and clouds. We find that the peak of the jet (latitudes 10° N to 10° S) suffers intense vertical shears reaching +2.5 ms−1 km−1, two orders of magnitude higher than meridional shears, and temporal variability above 1 bar altitude level.

Saturn's Global Zonal Winds Explored by Cassini/VIMS 5‐μm Images

“…Previous measurements of the VIMS zonal winds in 2004–2008 (Choi et al, ), which have the roughly same time frame as the ISS wind profile (Figure ), suggest even stronger equatorial winds. Therefore, we think the equatorial zonal winds are stronger by at least 50 m/s at the 2,000 hPa pressure level than at the 300–500 hPa pressure level, which is consistent with the analysis in a previous study (Sanchez‐Lavega et al, ).…”

“…Such a vertical shear of zonal winds in the middle and high latitudes is opposite to that in the equatorial region (5°S-5°N), in which the zonal winds are stronger at 2,000 hPa than at 300-500 hPa. It should be mentioned that it is also possible that the differences of zonal winds in the middle and high latitudes between the two pressure levels are due to the temporal variations, even though previous studies of the ISS winds (Garcia-Melendo, Perez-Hoyos, et al, 2011;Li et al, 2011;Sanchez-Lavega et al, 2016) and our examination of the temporal variations of the VIMS winds ( Figure 4) suggest that both of the ISS and VIMS zonal winds are likely stable over time in most latitudes.…”

“…Figure 1 displays the global profile of the VIMS 5-μm zonal winds around 2,000 hPa, which is compared with the global profile of the Cassini ISS continuum band zonal winds around 300-500 hPa. The VIMS 46 and ISS wind profiles shown in Figure 1 are from different times (VIMS winds mainly in 2015-16 and ISS winds mainly in 2004-08), but previous studies (e.g., Li et al, 2011;Sanchez-Lavega et al, 2016) suggest that the ISS zonal winds around 300-500 hPa did not significantly change with time during the Cassini period The investigations of the temporal variation of the VIMS zonal winds are lacking. Therefore, we cannot rule out the possibility that the difference between the two wind profiles shown in Figure 1 is due to temporal variations, even though it is more likely that the difference is due to the vertical shear of zonal winds on Saturn because the VIMS images and the ISS images probe different pressure levels.…”

“…The continuum band images recorded by the Cassini Imaging Science Subsystem (ISS; Porco et al, 2004) have been widely used to explore Saturn's zonal winds at the same level as the top visible clouds (e.g., Antuñano et al, 2015;Del Genio et al, 2007;Del Genio & Barbara, 2012;Dyudina et al, 2008Dyudina et al, , 2009Garcia-Melendo et al, 2010;Garcia-Melendo, Perez-Hoyos, et al, 2011;Li et al, 2011;Porco et al, 2005;Sanchez-Lavega et al, 2016;Sayanagi et al, 2013;Vasavada et al, 2006). The top visible clouds on Saturn are generally referred to as the ammonia clouds (e.g., West, 1983), residing around the 300-500 hPa pressure level (e.g., Perez-Hoyos & Sanchez-Lavega, 2006a;Tomasko & Doose, 1984;West, 1983).…”

Saturn atmospheric dynamics one year after Cassini: Long-lived features and time variations in the drift of the Hexagon

“…A bright White Spot (WS) in the North Equatorial Zone (NEZ) at 6.7±1.6 • N appeared in 2014 and was visible in many amateur observations acquired in 2014 and 2015. Sánchez-Lavega et al (2016) reported on the properties of this feature based on Cassini ISS images, ground-based data and HST images acquired on 29-30 June 2015. The bright cloud moved at 450 ms −1 .…”