Papers by Shawn Brueshaber
<p>On November 29<sup>th</sup>, 2021, the Juno Spacecra... more <p>On November 29<sup>th</sup>, 2021, the Juno Spacecraft completed its 38<sup>th</sup> perijove as part of its Extended Mission. Three of the spacecraft’s instruments, JunoCam, JIRAM, and MWR, imaged a thunderstorm in the North Equatorial Belt (NEB) at approximately 9<sup>o</sup>N planetocentric latitude.  JunoCam and the MWR captured data from an altitude of a few thousand kilometers, following JIRAM’s images of the storm four hours before. Ground-based observers tracked this storm over a period of a few days, providing a planetary-scale perspective to Juno’s observations.  This region of the planet has been quite active throughout 2021 and 2022. </p><p> </p><p>The morphology of the storm as shown in JunoCam’s RGB filters (observations with the methane filter were not conducted), and from ground-based observers, is highly suggestive of a moist-convective thunderstorm complex with clouds reaching the upper troposphere. Furthermore, JunoCam images suggest that the storm is shaped by vertical shear as the presumed anvil is offset from a thicker region of white clouds. On Earth, vertical shear is necessary for non-tropical cyclone thunderstorm systems to persist for prolonged periods.  JunoCam imaging also suggests a previous anvil top located to the west of the optically thick clouds, which may indicate a temporarily-varying nature to the convection, which is consistent with ground-based observations showing upwelling at this location for several days before the Juno images. JIRAM’s observations show a cold spot at 4.78 µm near the region of the thickest white clouds, which would be expected from optically thick clouds blocking heat transport to space. Spectroscopic retrievals show a slight enhancement of H<sub>2</sub>0 and PH<sub>3</sub> compared to the surrounding region, which is expected from upwelling from the interior. The microwave radiometer (MWR) instrument detected numerous lightning flashes at 0.6 GHz (Channel 1) and several flashes at 1.2 and 2.4 GHz (Channels 2 and 3, respectively), which are correlated with JunoCam and JIRAM’s observations of optically thick clouds.  However, the brightness temperature signals of the storm in the MWR observations appears to be confined to the upper most 9 bars of the atmosphere ("weather layer") indicating that a deep-seated convective plume originating from beneath the water-cloud base is probably not responsible for this storm system.  Instead, a humidity or temperature front contained within the weather layer may be a likely source.</p><p> </p><p>These observations may ultimately shed light on the mechanisms that form, sustain, and characterize moist convective storms in hydrogen-dominated atmospheres.  Here we summarize our observations to date and compare the PJ38 storm to other storms in Jupiter's NEB and those on Saturn. </p>
Remote Sensing, Dec 30, 2022
<p>The Juno spacecraft’s polar orbit with periapses (perijove; PJ) wi... more <p>The Juno spacecraft’s polar orbit with periapses (perijove; PJ) within a few thousand kilometers of the 1-bar level has allowed for detailed observations of Jupiter’s thunderstorms from multiple instruments at unprecedented resolution.  Here, we detail the observations of a 2,500-km wide thunderstorm feature located in the North Equatorial Belt (at planetocentric latitude 9°N; Fig. 1) from the six channels of the Microwave Radiometer Instrument (MWR), from JunoCam’s RGB filters, from the Jovian Infrared Auroral Mapper’s (JIRAM) 5-micron band, and from supporting Earth-Based images taken during near the time of the 38<sup>th</sup> perijove. Juno flew over one such thunderstorm complex at close range (~5,000 km) on 29 Nov. 2021 for the first time with a favorable alignment to observe such a feature at low emission angles. JunoCam and MWR observations were taken nearly simultaneously while JIRAM’s data was collected approximately 4.5 hours prior. </p> <p>Moist convection is widely thought to play a large role in transporting heat from Jupiter’s interior through the weather layer (here defined as 10 to 0.7 bar) and then to space. In the process, heat transport allows for moist convection, which powers thunderstorms and generates small-scale turbulence that, through the inverse-cascade mechanism, generates large-scale vortices and zonal jets.  Convective instability allows for strong updrafts that carry volatiles such as NH<sub>3</sub> and H<sub>2</sub>O from the base of the water-cloud (and deeper) upwards to form cumulonimbus (CB) clouds.  The tops of these CB towers diverge outwards and are shaped by local winds to form an icy anvil cloud much as they do on Earth.</p> <p> </p> <p>Lightning is a defining characteristic of CB clouds and the MWR instrument detected numerous flashes in and around the bright white feature with a storm-like morphology clearly observed by JunoCam. JIRAM’s M-band filter images clearly show the structure of the cloud tops, matching observations from JunoCam once the zonally-averaged motion over the 4.5-hour time separation is accounted for. Figure 2 is a JIRAM image with a noticeable dark ‘notch,’ which is where the optically thick storm clouds are located. Preliminary spectral analysis from JIRAM shows a slightly enhanced signal of H<sub>2</sub>O and PH<sub>3</sub> near the anvil top but NH<sub>3</sub> ice is undetectable in these night-time JIRAM observations.</p> <p> </p> <p>Gaseous NH<sub>3</sub> and H<sub>2</sub>O are partially opaque to wavelengths sensed by the MWR instrument.  Each of the six channels of MWR have a sensitivity that peaks at different altitudes in the atmosphere, which allows us to sound the brightness temperature and the vertical structure from the cloud tops down to many tens of bars.  The brightness temperature is a combination of air temperature and humidity, and, at present, we are unable to deconvolve these two measurements. Nevertheless, sounding the brightness temperature provides information on the depth and structure of a tall atmospheric feature and we present brightness temperature maps for all six channels.</p> <p>We observe that this particular thunderstorm complex is visible from the cloud tops (~0.7 bar) down to approximately the level of the water cloud. Below this level, the thunderstorm signal is no longer apparent, which indicates that any dry convective updraft carrying MWR opacity-inducing vapor is either not present, or its air temperature and humidity are combined in such a way to mask its presence perfectly. If this thunderstorm is a result of dry convection from below the base of the water cloud lifting moist air to the level of free convection (LFC) then the effect of the dry convection is to lift vapor already located around the base of the water-cloud level rather than bringing up significantly moist air from deep below the base of the water cloud, or otherwise a signal would be detected in the short wavelength channels of MWR (See Fig. 3 for a cloud-top MWR map).</p> <p>The next several perijoves will feature an orientation for the MWR instrument that is conducive for low emission angle observations. Additionally, the latitude of perijove is slowly migrating northward and, if Juno does fly over new thunderstorms, we may have the opportunity to compare the vertical structure of multiple thunderstorms taken from different regions of the planet at high resolution from multiple instruments.</p> <p><img src="" alt="" /></p> <p>Figure 1: PJ38 Thunderstorm from JunoCam Image JNCE_2021333_38C00030_V01 (left) and close-up  (right: Image Credit:…
<p>The Juno Microwave Radiometer (MWR) has extended our knowledge of the structure ... more <p>The Juno Microwave Radiometer (MWR) has extended our knowledge of the structure and composition of Jupiter's atmosphere down to several hundred bars, revealing meridional variability at great depths (e.g. Li et al. 2017, Fletcher et al. 2021). It has revealed that some cyclonic and anticyclonic vortices may have roots at depths of hundreds of bars of pressure (Bolton et al. 2022), but 5-µm hot spots and associated plumes are restricted to shallow depths above the water cloud (Fletcher et al. 2021). We report ongoing work on evolution of axisymmetric bands, concentrating on two regions where large-scale changes have been observed in the visible and infrared.</p> <p>One of these is the Equatorial Zone (EZ), for which Figure 1 illustrates a dramatic color change. The color change in the central component (EZc, ~3°S – 1°N, planetocentric latitude) is more prominent than the northern component (EZn, ~2° - 6°N).  This change began in 2018, and by 2019 was as prominent as shown in 2021. In near-infrared bands of strong gaseous absorption, the EZc reflectivity increased dramatically (Fig. 2), but only temporarily for the EZn.</p> <p>Another region is the northern component of the North Equatorial Belt (NEBn, ~12°N to 15°N), whose change from a visibly dark to a bright region is also illustrated in Figure 1, with the southern component (NEBs, ~7°N to 11°N) remaining its typical dark color.  Figure 3 shows that this color is associated with a remarkable drop of its 5-µm brightness which dropped down to the faint emissions of the nearby cloudy and visually bright zones. This implies a major increase in the opacity of 0.7-5 bar clouds that are similar but more extreme than the quasi-periodic northward expansions of the NEB (Fletcher et al. 2017). This transformation took place in early 2021 when Jupiter was in solar conjunction.</p> <p>The very preliminary results of our initial examination of MWR observations (Fig. 4) plot antenna temperatures derived using averages over all longitudes sensed in which the center of the field of view lay within specified latitude ranges. Observations were selected only if 99% or more of the field of view included the planet and the emission angle was limited to 65° or less, after which they were converted to a nadir-equivalent emission using limb-darkening models that were fit to every latitude and each channel. All observations were made at close approaches of the spacecraft to Jupiter, known as ‘perijoves’ or PJs. Many perijoves between 2019 and 2022 did not contain any measurements of these regions meeting those selection criteria, due to unfavorable spacecraft pointing. Exceptions included special spacecraft orientations.    </p> <p>The EZc appears invariable in time, but the EZn underwent a ~7K drop in Channel-3 antenna temperatures - sensitive to conditions near ~9 bars - starting in early 2017, reaching a minimum in late 2017, then returning to its original values by early 2019.  Similar variability is evident in Channel 4, sensitive to the ~3-bar level, and a smaller one in Channel 5, which is sensitive to the ~1.5-bar level.  No change is detectable in Channel 6, sensitive to the ~0.7-bar level. The 2017 temperature drop has no obvious counterpart in reflected sunlight, although its “recovery” occurs during the reflectivity changes in 2019 (Figs. 1-2). To link the two, one must devise a causal relationship between a short-lived variation of absorber, likely gaseous ammonia, at 1.5-9 bars at 2016-2019 between 2°N and 6°N, and conditions at higher altitudes over a wider latitude range.</p> <p>If the NEBn variability between 2020 and 2021 (Figs. 1, 3) implies an increase of ammonia absorption, we would expect a decrease in antenna temperatures between our last trustworthy observation in 2019 April and observations in late 2021. This is indeed the case at 0.7 bars, represented by the 6-7K drop in Channel-6 antenna temperatures for the NEBn. This is also present in Channel 5 as a ~5K drop, but it is not detectable above the noise in the deeper-sounding channels, so this is not substantially present at pressures higher than ~1.5 bars. A ~5K drop in antenna temperatures in late 2016 is followed by a slower rise to its previous range by the end of 2017 in both Channels 5 and 6. Other channels do not show this variability, so this is another “shallow” phenomenon with no obvious connection to changes in cloud reflectivity.</p> <p>We will continue to examine variability in cloud reflectivity associated with these changes,  observe with increasingly favorable geometries for the next few perijoves, and examine other latitudes for variability.</p>…
<p>Jupiter’s cyclonic features are known to undergo transitions betwe... more <p>Jupiter’s cyclonic features are known to undergo transitions between quiescent states with smooth edges (often appearing as dark brown ‘barges’) to states with convective outbursts of billowing white clouds, chaotically churned into filamentary structures.  Cyclones in the latter state are known as ‘Folded Filamentary Regions’ (FFRs), and Voyager images (Ingersoll+1979, doi: 10.1038/280773a0) revealed them to be rapidly-varying turbulent regions, occurring in cyclonic domains on the poleward side of Jupiter’s prograde jets.  JunoCam visible-light observations (Orton+2017, doi:10.1002/2016GL072443, Rogers+2021, doi:10.1016/j.icarus.2021.114742), reveal the increasing prevalence of FFRs at mid-to-high latitudes.  They dominate the polar domain alongside smaller anticyclonic white ovals, drifting westward in latitude bands between the narrow prograde jets, and rapidly evolving over timescales of days. </p><p>The present study makes use of Juno’s ever-improving microwave observations of the north polar domain, as the latitude of closest-approach (“perijove”) moves northward.  We therefore focus on FFRs in the northern hemisphere, where we find them to occur in zonally-organised latitude bands even at high latitudes.  Statistics of the FFRs suggest that they occur on the poleward sides of the N4 (43.3<sup>o</sup>N, centric), N5 (52.3<sup>o</sup>N), and N7 (66.1<sup>o</sup>N) prograde jets (N6 at 61.2<sup>o</sup>N coincides with a ‘bland zone’ lacking notable FFRs), and scattered in the polar domain up to the octagon of circumpolar cyclones at 85<sup>o</sup>N.  JIRAM 5-µm imaging of both poles reveal FFRs as generally dark structures with elevated aerosol opacity blocking thermal infrared emission from the 4-6 bar level, coinciding with the white stratiform clouds observed by JunoCam. Clusters of small cumulus-like clouds, as well as curvilinear cloud streaks, provide texture to the flat stratiform clouds to give the appearance of a network of filaments.  Visibly-dark lanes border the brighter filaments, creating an intricate network of narrow, aerosol-free, and 5-µm-bright striations within each FFR.  This is in contrast to cyclonic features such as barges at lower latitudes, where an absence of overlying aerosols generally renders them 5-µm bright. </p><p>A survey of 1.4-50 cm observations acquired by Juno’s Microwave Radiometer (MWR) between PJ20 (May 2019) to PJ37 (October 2021) reveals that FFRs share a key characteristic with their low-latitude counterparts:  they are microwave-bright in channels sounding the 0.6-2.0 bar range (1.4-3.0 cm), become hard to distinguish from their surroundings near 5 bars (5.75 cm), but are then microwave-dark in the channel sounding 10-15 bar (11.5 cm). This suggests FFRs are depleted in ammonia gas and/or locally warmer at levels above the putative location of Jupiter’s water cloud, the latter implying a decay of cyclonic winds with altitude.  This shallow ammonia depletion is surprising, given the apparent convective nature of the FFRs - maybe NH<sub>3</sub>-rich plumes occupy a sufficiently small area of the cyclonic structure, so that they have negligible impact on the warm emission observed by MWR.  This shallow depletion is balanced by a local NH<sub>3</sub> enrichment (or local cooling) at depth, below the water cloud, like a cyclonic lens.  However, the extension of FFR signatures to deeper levels (p>20 bars) is currently unclear due to insufficient spatial coverage and resolution at the longest-wave channels, and confusion arising from auroral contributions to the MWR dataset at 50 cm.  </p><p>An inversion in microwave brightness with depth was previously identified for Jupiter’s larger-scale belts and zones (Fletcher+2021, doi:10.1029/2021JE006858) and mid-latitude discrete features (Bolton+2021, doi:10.1126/science.abf1015), and now appears to be common at high latitudes as well.  Geostrophy implies that cyclonic circulations (low-pressure centers) cause a rise in potential-temperature surfaces in deeper layers, potentially triggering moist convection in the water cloud (e.g., Dowling & Gierasch, 1989 Bull. Amer. Astron. Soc 21, 946; Fletcher+2017, doi:10.1016/j.icarus.2017.01.001), producing the distinct convective cloud structure observed by visible and infrared imaging: juxtaposed tall convective towers, deep water clouds, and narrow clear lanes (Imai+2020, doi:10.1029/2020GL088397). Lightning sferics measured by MWR at 50 cm/600 MHz are more frequent in the N4, N5, and N7 domains where FFRs are common…
<p><strong>Introduction</strong></p> &... more <p><strong>Introduction</strong></p> <p>The extended portion of NASA’s Juno mission began on 1 August 2021 and will continue through September 2025. The extended mission expands Juno’s science goals beyond those of the prime mission, as noted at the last EPSC (Orton et al.  EPSC2021-58).  Atmospheric studies will continue to be among the foremost of science goals and an area in which the world-wide community of Jupiter observers can provide significant contextual support.  Juno’s remote-sensing observations will take advantage of the migration of its closest approaches (“perijoves” or PJs) toward increasingly northern latitudes.  The observations should include close-ups of the circumpolar cyclones and semi-chaotic cyclones known as “folded filamentary regions”. A series of radio occultations will provide vertical profiles of electron density and the neutral-atmospheric temperature over several atmospheric regions. The mission will also map the variability of lightning on Jupiter’s night side.</p> <p><strong>Physical Details of the Mission</strong></p> <p>The sequence of orbits and key investigations of the primary and extended missions are shown in Figure 1.  We note that on PJ34, the orbital period was reduced from 53 days to 43-44 days. It will be reduced shortly after this meeting on PJ45 to 38 days and again on PJ57 to ~33 days.</p> <p><img src="" alt="" width="1015" height="914" /></p> <p><em>Figure 1. Progression of Juno orbits viewed from above Jupiter’s north pole with respect to local time of day. “PJ” designates a “perijove”, the closest approach to Jupiter on each numbered orbit. Following a Ganymede flyby on PJ34 (green orbit), the orbital period decreased from 53 days to 43-44 days (green + blue orbits). The “Great Blue Spot” (blue) orbits map an isolated patch of intense magnetic field. Following a close Europa flyby on PJ45 (aqua orbit), the period will decrease to ~38 days (orange orbits). Following close flybys of Io on PJ57 and PJ58 (black orbits) the period will decrease  to ~33 days (red orbits). In reflected sunlight, Jupiter will mostly appear as a crescent at perijoves following PJ58. </em></p> <p>Some characteristics of perijoves of the extended mission are shown in Table 1. We caution that while the day of year for the perijoves is reasonably fixed, the exact times may change by hours in either direction and the longitudes will change accordingly.  Timing for later orbits up to PJ76, may be affected by currently unmodeled anomalies in satellite masses that could change dates and times.</p> <p><img src="" alt="" width="1061" height="597" /></p> <p><em>Figure 2</em><em>.</em><em> Expected latitudes and longitudes to be measured by the 20 radio occultations of the Juno spacecraft between PJ52 and PJ77. Locations of ingress lie largely in the northern hemisphere - locations of egress in the southern hemisphere. Locations of the Galileo Probe and Voyager-1 radio occultations are also shown for reference. </em></p> <p><strong>Role of Amateur Astronomers</strong></p> <p>We’ve noted in the past at previous EPSC meetings how amateurs can contribute to the Juno mission via their collective world-wide 24/7 coverage of Jupiter. This applies also to the cadre of professional astronomers supporting the Juno mission and its reconnaissance of  the Jupiter system over a broad spectral range. In the past, these have alerted observers to strong interactions between the Great Red Spot and smaller anticyclones (Sanchez-Lavega et al. 2021. <em>J. Geophys. Res</em>. <strong>126</strong>, e006686) and the occurrence and evolution of prominent and unusual vortices, such as “Clyde’s spot” (Hueso et al. 2022. <em>Icarus</em> <strong>380</strong>,114994). During the last apparition, observations were made with the NASA Infrared Telescope Facility (IRTF) that showed slow-moving bright patches in the Equatorial Zone (EZ) that were observed more continuously among the amateur community with 890-nm (“methane”) filters. We also identified an intense 5-µm spot detected using IRTF imaging that coincided with an unusually dark spot in amateur methane-filtered images. The continued tracking of outbreaks in the southern part of the North Equatorial Belt (NEB) also greatly informed the Juno team and supporting astronomers regarding the systematic longitudinal distribution of outbreaks and the range of atmospheric features they generate. A perijove-by-perijove…
AAS/Division for Planetary Sciences Meeting Abstracts #48, Oct 1, 2016
AGU Fall Meeting Abstracts, Dec 7, 2020
My research investigates the polar atmospheric dynamics of the giant planets: Jupiter and Saturn ... more My research investigates the polar atmospheric dynamics of the giant planets: Jupiter and Saturn (gas giants), and Uranus and Neptune (ice giants). I conduct my research modifying and applying the Explicit Planetary Isentropic Coordinate global circulation code to model the polar regions of the four giant planets. The motivation behind my research is to uncover the reason why giant planet polar atmospheric dynamics differ. Jupiter features multiple circumpolar cyclones arranged in geometrical configurations, whereas Saturn features a single pole-centered cyclone. Uranus and Neptune also appear to have single pole-centered cyclones, albeit, larger than those on Saturn. It is widely accepted that moist-convective processes such as thunderstorms, are a leading candidate in generating small-scale turbulence, which self-organizes into larger structures, via a process called the inverse-cascade. In the polar regions, cyclonic vortices are the naturally preferred outcome of this self-organization. I model small-scale turbulence by continually adding or removing mass into the domain throughout the simulation at scales matching the size of thunderstorms. The continual injection of turbulence is known as a "forced-turbulence" model. The storms geostrophically balance into small cyclones (anticyclones) if mass is removed (added). Cyclones (anticyclones) drift poleward (equatorward) via the beta-drift mechanism, which leads to an accumulation of cyclonic vorticity at the pole. The resulting configurations, dynamics, and morphologies of polar cyclones are the subject of my numerical simulations. In Chapter 4, I show that the Burger Number, Bu-the ratio of the Rossby deformation radius to the planet radius squared-controls the morphology and number of polar cyclones. If Bu is sufficiently small, as expected for Jupiter, multiple circumpolar cyclones emerge from the forced-turbulent simulations. If Bu is sufficiently large, as expected for Saturn and the ice giants, a single pole-centered cyclone emerges instead. Four dynamical regimes are found
<p>Multi-Instrument Observations of a Jovian Thunderstorm from Juno and Ground-Base... more <p>Multi-Instrument Observations of a Jovian Thunderstorm from Juno and Ground-Based Telescopes</p><p> </p><ul><li>Brueshaber<sup>1</sup>, G. Orton<sup>1</sup>, S. Brown<sup>1</sup>, S. Levin<sup>1</sup>, A. Ingersoll<sup>2</sup>, C. Hansen<sup>3</sup>, D. Grassi<sup>4</sup>, A. Mura<sup>4</sup>, L. N. Fletcher<sup>5</sup>, S. Bolton<sup>6</sup></li> </ul><p> </p><p>On November 29<sup>th</sup>, 2021, the Juno Spacecraft completed its 38<sup>th</sup> perijove as part of its Extended Mission. Three of the spacecraft’s instruments, JunoCam, JIRAM, and MWR, imaged a thunderstorm in the NEB at approximately 9<sup>o</sup>N planetocentric latitude.  JunoCam and the MWR captured data from an altitude of a few thousand kilometers, following JIRAM’s images of the storm four hours before. Ground-based observers tracked this storm over a period of a few days, providing a planetary-scale perspective to Juno’s observations.</p><p> </p><p>The morphology of the storm as shown in JunoCam’s RGB filters (observations with the methane filter were not conducted), and from ground-based observers, is highly suggestive of a moist-convective thunderstorm complex with clouds reaching the upper troposphere. Furthermore, JunoCam images suggest that the storm is shaped by vertical shear as the presumed anvil is offset from a thicker region of white clouds. On Earth, vertical shear is necessary for non-tropical cyclone thunderstorm systems to persist for prolonged periods.  JunoCam imaging also suggests a previous anvil top located to the west of the optically thick clouds, which may indicate a temporarily-varying nature to the convection, which is consistent with ground-based observations showing upwelling at this location for several days before the Juno images. JIRAM’s observations show a cold spot at 4.78 µm near the region of the thickest white clouds, which would be expected from optically thick clouds blocking heat transport to space. Spectroscopic retrievals show a slight enhancement of H<sub>2</sub>0 and PH<sub>3</sub> compared to the surrounding region, which is expected from upwelling from the interior. The MWR instrument detected numerous lightning flashes at 0.6 GHz (Channel 1) and several flashes at 1.2 and 2.4 GHz (Channels 2 and 3, respectively), which are correlated with JunoCam and JIRAM’s observations of optically thick clouds.</p><p> </p><p>Given the close approach of the Juno spacecraft with three instruments observing the storm, this feature may be the most highly instrumented observation of a Jovian thunderstorm to date. The cloud morphology, size, optical thickness of its clouds, and lightning detection in this feature suggest that the storm is probably the equivalent of a terrestrial mesoscale convective complex, possibly composed of multiple individual thunderstorms as is the case on Earth.  However, differences between jovian and terrestrial thunderstorms exist, most notably the lack of a surface to help focus convection and the composition of the atmosphere.  Nevertheless, the observations that we detail here may ultimately shed light on the mechanisms that form, sustain, and characterize moist convective storms in hydrogen-dominated atmospheres.  Here we summarize our observations to date and perform a preliminary comparison to terrestrial and Saturnian thunderstorms.</p><p> </p><p><sup>1</sup> Jet Propulsion Laboratory and California Institute of Technology</p><p><sup>2 </sup>California Institute of Technology</p><p><sup>3</sup> Planetary Science Institute</p><p><sup>4</sup> Institute for Space Astrophysics and Planetology INAF-IAPS</p><p><sup>5</sup> School of Physics and Astronomy, University of Leicester</p><p><sup>6</sup> Southwest Research Institute</p>
MISSION CONCEPT FROM THE 2017 NASA-JPL PLANETARY SCIENCE SUMMER SEMINAR. M. C. Bouchard, S. M. Ho... more MISSION CONCEPT FROM THE 2017 NASA-JPL PLANETARY SCIENCE SUMMER SEMINAR. M. C. Bouchard, S. M. Howell, L. Chou, M. Thompson, S. Cusson, M. Marcus, H. Brodsky Smith, S. Bhattaru, J. J. Blalock, S. Brueshaber, S. Eggl, E. R. Jawin, K. E. Miller, M. Rizzo, K. Steakley, N. H. Thomas, K. Trent, M. Ugelow, C. J. Budney and K. L. Mitchell. Washington Univ. in St Louis, St. Louis, MO, JPL, CalTech, Pasadena, CA (PI: [email protected]), Univ. Illinois at Chicago, Chicago, IL, NASA JSC, Houston, TX , Univ. Michigan, Ann Arbor, MI , Univ. Maryland College Park, College Park, MD , ASU, Tempe, AZ, MIT, Cambridge, MA, Hampton Univ., Hampton, VA, Western Michigan Univ., Kalamazoo, MI, Brown Univ., Providence, RI, SwRI, San Antonio, TX, NASA GSFC, Greenbelt, MD, New Mexico State Univ. Main Campus, Astronomy, Las Cruces, NM, CalTech, Pasadena, CA, Univ. Colorado at Boulder, Boulder, CO
Bulletin of the AAS, 2021
Icarus, 2021
Summary Previous studies of Jupiter's wind patterns revealed the southernmost two prograde je... more Summary Previous studies of Jupiter's wind patterns revealed the southernmost two prograde jets at 58°S and 64°S (planetocentric), which we designate as the S5 and S6 jets, respectively, but the jets and the wind patterns further poleward were not well defined. The Juno mission has provided the first opportunity to study the South Polar Region (SPR). Here we use images from Juno's camera, JunoCam, to characterize these jets and the wind patterns further south. We measure the main wind systems using JunoCam images taken up to two hours apart. The S5 jet coincides with a slightly sinuous boundary in methane-band images. The S6 jet is faster, broader and highly undulating in latitude, generally coinciding with the sinuous edge of the methane-bright South Polar Hood, whose wave pattern is often regular with a mean wavelength of 25.5° (±2.6°) longitude. Peak wind speeds along the S6 jet range from 42 (±12) to 49 (±11) m/s, faster than previously recognized. Poleward of the S6 jet, at ~65–70°S, there is an irregular belt of chaotic cyclonic regions termed folded filamentary regions (FFRs), with several small anticyclonic white ovals (AWOs) on or near its southern edge. Some of these FFRs appear to be extending northeast into the S6 jet. More FFRs are scattered from ~70 to 80°S. Wind speeds in the FFRs are generally ~20–60 m/s, comparable to lower-latitude cyclonic circulations. We also generate semi-quantitative maps of local vorticity, and thence, mean zonal vorticity profiles as a function of latitude. These confirm the S6 jet as sinuous and the southernmost belt of FFRs as a stable belt. Further south, there is usually a weak cyclonic vorticity maximum near 78°S, which probably represents irregular structures such as FFRs. Supplementary ground-based images, spaced by up to 4 days, show westward drifts for the ~65–70°S belt, with a mean of ~ + 0.9°/day in System III longitude. AWOs can also be tracked, for months or even years. They drift westward with a uniform speed of +0.8°/day between 69.5 and 72.4°S, but towards higher latitudes, up to 76°S, they show a steep latitudinal gradient to faster (eastward) speeds, comparable to those measured around the south polar pentagon of circumpolar cyclones at ~80°S. Overall, the ~65–70°S belt and associated AWOs show dynamical behaviour similar to lower latitudes. Further south, there are no rapid continuous jets, but the loose enhancement of cyclonic structures near 78°S suggests a trace of zonal structure extending almost as far as the polar pentagon.
Bulletin of the AAS, 2021
Journal of Geophysical Research: Planets, 2019
The paper presents velocity fields with ~3-km spatial resolution of Saturn's north polar vortex (... more The paper presents velocity fields with ~3-km spatial resolution of Saturn's north polar vortex (NPV) retrieved using the optical flow method from a sequence of polar-projected cloud images captured by the Imaging Science Subsystem camera on board NASA's Cassini spacecraft. The fields of the velocity magnitude, velocity variation, relative vorticity, divergence and second invariant are determined to characterize the flow structures of the inner core of the NPV. The mean zonal and mean meridional velocity profiles of the NPV are compared with previous measurements. We also describe the relevant details of application of the optical flow method to planetary cloud tracking wind measurements. The mean zonal velocity profile is consistent with the previous measurements using correlation image velocimetry methods. The small but significant meridional velocity corresponds to outwardly spiraling streams observed in the region near the north pole (NP). The concentrated vorticity and second invariant within 1-degree planetographic latitude of the NP indicate strong rotational motion of the fluid. An analysis is presented to explore a possible physical origin of the observed spiraling node at the NP.
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Papers by Shawn Brueshaber