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We measured the horizontal winds in Jupiter's Great Red Spot (GRS) using data from the WFC3/UVIS instrument on board the Hubble Space Telescope (HST). The data cover 11 epochs from 2009 to 2020. Long‐term monotonic trends in size and shape previously noted from the visible cloud appearance are paralleled by changes in the high‐speed ring around the vortex. The circularization of the GRS cannot be explained by changes in the horizontal wind shear of the surrounding environment. The velocity fields suggest no long‐term trend in the static stability inside or outside the vortex. Instead, the changes are accompanied by a 4%–8% increase in the mean wind speeds of the high‐speed ring from 2009 to 2020. Changes in the wind field coincided with the South Equatorial Belt Outbreak storms of 2016–2017, but not with 2019 "flaking" events involving detachment of red material from the main oval. Plain Language Summary: We measured the horizontal winds in Jupiter's Great Red Spot (GRS) using data from the WFC3/UVIS instrument on board the Hubble Space Telescope (HST). The data cover 11 time periods from 2009 to 2020. Winds blow fastest in a high‐speed ring around the outside of the GRS. Previous pictures of the clouds showed that the GRS was shrinking and becoming more like a circle and less like an oval. We measure similar changes in the high‐speed ring. We rule out some possible causes for the changes: changes in the wind shear of the surrounding atmosphere, or changes in how temperature varies with height. As the GRS shrinks and circularizes, the average wind speed in the high‐speed ring gets faster. Some changes in the GRS wind patterns happened at the same time as a giant nearby storm in 2016/2017, but we did not find changes at the same time as flaking events in 2019. By "flaking" we mean pictures showing that small areas of red, normally kept inside the GRS, detached and blew away from the spot. Key Points: A high‐speed ring marking the edge of the Great Red Spot velocity field has been shrinking and circularizing at a roughly constant rateMean wind speeds within the high‐speed ring have increased by 4%–8% from 2009 to 2020, at a roughly constant rateVelocity field changes coincided with a major 2016 storm, but we found no changes in 2019 when red material flaked away from the main oval [ABSTRACT FROM AUTHOR]

An examination of the dynamics of the middle atmosphere as reconstructed in the NASA Modern‐Era Retrospective analysis for Research and Applications, Version 2 (MERRA‐2) reveals the formation of large scale three‐dimensional (3D) vortices in the tropical stratosphere following both the vernal and autumnal equinoxes at times when the jet associated with the westerly phase of the semiannual oscillation (SAO) is maximal and extratropical influences from planetary waves are weakest. An empirical orthogonal function (EOF) analysis of the second matrix invariant of the velocity gradient tensor applied to the shear zones about the SAO reveals statistically stationary wave‐5 vortex structures that span more than 3,200 km in length and up to 40 km in the vertical. Eliassen‐Palm fluxes suggests the vortices are maintained by a combination of local (shear zones) and remote (vertically propagating tropical) sources of momentum. These large‐scale coherent features appear to be unique to the stratopause. Plain Language Summary: Application of methods commonly employed in engineering fluid mechanics to visualize vortices are used to examine a recent state of the art reconstruction of the middle atmosphere. This analysis reveals huge vortical structures present during the equinoctial seasons in the region of the tropical stratopause. These semiannual coherent features appear to be unique to the middle atmosphere spanning up to 30° longitude at ±15° latitude corresponding to around 3,200 km in length and between 10 hPa and 0.1 hPa encompassing up to 40 km in the vertical. Key Points: Empirical orthogonal function (EOF) analysis of the second matrix invariant of the velocity gradient tensor is applied to the shear zones about the tropical stratosphereWe identify large scale vortices near the tropical stratopause as reconstructed in the NASA MERRA‐2 atmospheric reanalysisThe vortices form following the vernal and autumnal equinoxes at times when the westerly jet is maximal [ABSTRACT FROM AUTHOR]

Submesoscale coherent vortices (SCVs) are numerous in high‐resolution numerical simulations, but their observations are scarce. Among the few in situ available measurements of SCVs, a vast majority concern anticyclones. No cyclonic SCV with large dynamical Rossby number (|ζ/f| > 1) has ever been sampled. This suggested that such small cyclones may lack robustness. Here, we present in situ measurements of an intense cyclonic SCV in the Arabian Sea. This eddy lay at 600 m depth, with a Rossby number Ro=O(1) and a dynamical Rossby number |ζ/f| > 1.5. This cyclone was most likely generated at the mouth of the Gulf of Aden. It trapped and advected Red Sea Water, from there on. This highlights the role of deep SCVs in the spreading of salty waters across the Arabian Sea. Plain Language Summary: Numerical simulations of the ocean reveal the presence of numerous submesoscale eddies, vortices with radii smaller than, or equal to, 10 km. Nevertheless, their observations at depth are scarce because sampling their hydrological and dynamical structures requires very high resolution measurements. The present study presents measurements of a deep submesoscale cyclone in the Arabian Sea, collected during the PHYSINDIEN 2019 experiment. This intense, submesoscale, subsurface cyclone was centered at 600 m depth; most likely, it was formed at the mouth of the Gulf of Aden. Then it carried highly saline waters from the Red Sea toward the open Arabian Sea. We underline that conditions leading to the formation of such submesoscale eddies are often met in this region. Thus, such deep eddies should be recurrent in this region and should play a key role in spreading salty waters. Key Points: A deep submesoscale cyclone was observed in the Arabian SeaThe cyclone contained Red Sea Water on its rimThis cyclone was generated at the mouth of Gulf of Aden, as a local current interacted with the bottom topography [ABSTRACT FROM AUTHOR]

The problem of transforming geospatial data into polar coordinates, a common task in the analysis of data centered on geophysical phenomena, is examined. The azimuthal equidistant projection is shown to be the optimal transform for this purpose. A mathematical and observational analysis of the errors incurred by using a common alternative transform is conducted and reveals that such errors can be significant at radii as small as a few hundred kilometers. When evaluating observed 200‐hPa wind fields near Atlantic tropical cyclones (TCs), median azimuthal maximum errors in total and radial wind range up to 10% within 700 km of the TC and up to 50% within 1,600 km of the TC. Errors are shown to depend strongly on the statistical characteristics of the data set and increase nonlinearly with latitude and radius. Plain Language Summary: Many analyses of Earth‐relative data benefit from transforming the data into different coordinate systems. For vortices, such as hurricanes, a polar coordinate system is often desirable or necessary. While converting data to polar coordinates is common, the process by which this is done can contain errors that are detrimental to any analysis performed with the data. In order to provide a reference for the magnitude of this problem, we evaluate how large these errors can be for theoretical and real‐world cases when using an approach commonly employed in contemporary studies. Results indicate that these errors can be substantial at radii as small as a few hundred kilometers, regardless of location on Earth. We show that utilizing a transform called the azimuthal equidistant projection will minimize these errors, so we recommend its use in vortex‐relative analyses. Key Points: The AE projection is ideal for transforming geospatial data to a feature‐centered polar spaceErrors incurred by using a common alternate transform can be substantial even at tropical latitudesThe recommended method for projecting scalar and vector fields onto polar spaces is provided [ABSTRACT FROM AUTHOR]