We will present a series of Great Red Spot (GRS) velocity fields, derived using the ACCIV tool (Asay-Davis et al. 2009) with data acquired by the WFC3 instrument on the Hubble Space Telescope (HST) between 2012 and 2020. The 2020 data are anticipated for 24-25 August, after the DPS abstract deadline. Thanks to the combination of annual observations through the OPAL program (Simon et al. 2015) and higher-frequency coverage (Wong et al. 2020) during the Juno mission (Bolton et al. 2017), we are able to investigate short timescale variation relevant to the “flakes” that drew attention in 2019 (e.g., Sanchez-Lavega et al. 2019, Marcus et al. 2019).
We will combine the WFC3 velocity fields with previously published datasets from HST/ACS, Cassini ISS, Galileo SSI, and Voyager to investigate longer-term evolution of the velocity field dating back to 1979. Preliminary analysis indicates a broad consistency with the long-term shrinking of the east-west size of the GRS based on its visible cloud area, a roughly linear rate of change dating back to 1879 (Simon et al. 2018). Unlike the east-west diameter, the north-south diameter defined by the velocity field instead has remained largely constant over the 1979-2019 period. The circularization of the GRS velocity field implies either a decrease in background zonal wind shear over the same time period, or an increasing potential vorticity of the vortex (which would in turn imply changes in the vertical structure of the vortex, the stratification of the background atmosphere, or the relative vorticity of the flow).
Asay-Davis et al. 2009 - DOI 10.1016/j.icarus.2009.05.001
Bolton et al. 2017 - DOI 10.1007/s11214-017-0429-6
Marcus et al. 2019 - 2019AGUFM.P13B3505M
Sanchez-Lavega et al. 2019 - https://ui.adsabs.harvard.edu/abs/2019AGUFM.P44A..01S
Simon et al. 2015 - DOI 10.1088/0004-637X/812/1/55
Simon et al. 2018 - DOI 10.3847/1538-3881/aaae01
Wong et al. 2020 - DOI 10.3847/1538-4365/ab775f