ArticlePublisher preview available

Clusters of Cyclones Encircling Jupiter's Poles

Authors:
Alberto Adriani at National Institute of Astrophysics
Alberto Adriani
A. Mura at National Institute of Astrophysics
A. Mura
Glenn S. Orton at California Institute of Technology
Glenn S. Orton
C. Hansen
C. Hansen
C. Hansen
  • This person is not on ResearchGate, or hasn't claimed this research yet.
Show all 32 authorsHide
Read publisher preview
Download citation
To read the full-text of this research, you can request a copy directly from the authors.

Abstract and Figures

The familiar axisymmetric zones and belts that characterize Jupiter’s weather system at lower latitudes give way to pervasive cyclonic activity at higher latitudes. Two-dimensional turbulence in combination with the Coriolis β-effect (that is, the large meridionally varying Coriolis force on the giant planets of the Solar System) produces alternating zonal flows. The zonal flows weaken with rising latitude so that a transition between equatorial jets and polar turbulence on Jupiter can occur. Simulations with shallow-water models of giant planets support this transition by producing both alternating flows near the equator and circumpolar cyclones near the poles. Jovian polar regions are not visible from Earth owing to Jupiter’s low axial tilt, and were poorly characterized by previous missions because the trajectories of these missions did not venture far from Jupiter’s equatorial plane. Here we report that visible and infrared images obtained from above each pole by the Juno spacecraft during its first five orbits reveal persistent polygonal patterns of large cyclones. In the north, eight circumpolar cyclones are observed about a single polar cyclone; in the south, one polar cyclone is encircled by five circumpolar cyclones. Cyclonic circulation is established via time-lapse imagery obtained over intervals ranging from 20 minutes to 4 hours. Although migration of cyclones towards the pole might be expected as a consequence of the Coriolis β-effect, by which cyclonic vortices naturally drift towards the rotational pole, the configuration of the cyclones is without precedent on other planets (including Saturn’s polar hexagonal features). The manner in which the cyclones persist without merging and the process by which they evolve to their current configuration are unknown.
Comparison of the polar cyclonic structures between PJ4 and PJ5 Here is the comparison between JIRAM 5-μm data acquired during PJ4 and PJ5. The letters identify possible recurrent structures and arrows show the suggested displacements that occurred in the 53-day interval between these two perijoves. The radiance scale is the same as in Fig. 1. When the region surrounding the north pole is not sunlit, there are no JunoCam observations of the NPC. Although the north pole was detected by JIRAM on PJ4, we were unable to determine whether or not it maintains a stable position over the geographic north pole because of insufficient coverage of the NPC during PJ5. However, the cyclonic structures A, B and C move northeast, migrating from the lower latitudes. The G and H internal structures, located between the NPC and the cyclones, are anticyclones and move westward in that narrow corridor between 85.5° N and 87° N to their new location observed during PJ5 between vortex D and the NPC. In contrast, JIRAM was able to observe the SPC in both PJ4 and PJ5. In fact, along with the cyclones G and H shown, the SPC moves northward, increasing its distance with respect to the geographic south pole by 1.5° between PJ4 and PJ5. On the other hand, JunoCam was able to observe the SPC at all perijoves, and found that it was always displaced from the south pole in approximately the same direction (towards a System III longitude of about 219° ± 21°), with its central latitude varying from 88.0° S at PJ1 up to 89.0° S at PJ4, and down to 88.4° S at PJ5. It remains to be seen whether this is a cyclic oscillation. The five cyclones remain at almost constant radial distances from the centre of the SPC (and thus not from the geographic south pole), so the whole pentagon drifts in latitude. Anticyclone A appears to move as much as about 1° south and about 24° east. It is forced and surrounded by the two cyclonic structures that consolidate themselves between PJ4 and PJ5 from the origins L, J, C and K. Finally, the anticyclone D disappears while F is expelled from its position and possibly moves to new position E.
Comparison of the polar cyclonic structures between PJ4 and PJ5 Here is the comparison between JIRAM 5-μm data acquired during PJ4 and PJ5. The letters identify possible recurrent structures and arrows show the suggested displacements that occurred in the 53-day interval between these two perijoves. The radiance scale is the same as in Fig. 1. When the region surrounding the north pole is not sunlit, there are no JunoCam observations of the NPC. Although the north pole was detected by JIRAM on PJ4, we were unable to determine whether or not it maintains a stable position over the geographic north pole because of insufficient coverage of the NPC during PJ5. However, the cyclonic structures A, B and C move northeast, migrating from the lower latitudes. The G and H internal structures, located between the NPC and the cyclones, are anticyclones and move westward in that narrow corridor between 85.5° N and 87° N to their new location observed during PJ5 between vortex D and the NPC. In contrast, JIRAM was able to observe the SPC in both PJ4 and PJ5. In fact, along with the cyclones G and H shown, the SPC moves northward, increasing its distance with respect to the geographic south pole by 1.5° between PJ4 and PJ5. On the other hand, JunoCam was able to observe the SPC at all perijoves, and found that it was always displaced from the south pole in approximately the same direction (towards a System III longitude of about 219° ± 21°), with its central latitude varying from 88.0° S at PJ1 up to 89.0° S at PJ4, and down to 88.4° S at PJ5. It remains to be seen whether this is a cyclic oscillation. The five cyclones remain at almost constant radial distances from the centre of the SPC (and thus not from the geographic south pole), so the whole pentagon drifts in latitude. Anticyclone A appears to move as much as about 1° south and about 24° east. It is forced and surrounded by the two cyclonic structures that consolidate themselves between PJ4 and PJ5 from the origins L, J, C and K. Finally, the anticyclone D disappears while F is expelled from its position and possibly moves to new position E.
… 
Annotated version of the JunoCam images of the poles The unannotated version is shown in Fig. 2. The composite components from each perijove pass that were used to create the figure are noted. Each corresponds to the polar image taken at a time that minimized the emission angle over most of the pole, as detailed in Extended Data Table 2. The PJ4 component is identical to its contribution in Fig. 1, with contributions from the other perijove passes, separated by approximately 90° in longitude, as noted. The northern cyclones forming the inner square (actually a rhombus) of the ditetragonal pattern are labelled by odd numbers and those forming the outer square by even numbers. The southern cyclones forming a quasi-pentagonal shape are numbered sequentially, with the largest spacing between cyclones labelled 1 and 5, indicated by the ‘gap’ label. Despite the time differences of 53 to 106 terrestrial days between JIRAM images acquired on PJ4, shown broadly in Fig. 1b and d, and JunoCam images in PJ1, PJ3 and PJ5, the positions of the cyclones are remarkably consistent in System III longitude.
Annotated version of the JunoCam images of the poles The unannotated version is shown in Fig. 2. The composite components from each perijove pass that were used to create the figure are noted. Each corresponds to the polar image taken at a time that minimized the emission angle over most of the pole, as detailed in Extended Data Table 2. The PJ4 component is identical to its contribution in Fig. 1, with contributions from the other perijove passes, separated by approximately 90° in longitude, as noted. The northern cyclones forming the inner square (actually a rhombus) of the ditetragonal pattern are labelled by odd numbers and those forming the outer square by even numbers. The southern cyclones forming a quasi-pentagonal shape are numbered sequentially, with the largest spacing between cyclones labelled 1 and 5, indicated by the ‘gap’ label. Despite the time differences of 53 to 106 terrestrial days between JIRAM images acquired on PJ4, shown broadly in Fig. 1b and d, and JunoCam images in PJ1, PJ3 and PJ5, the positions of the cyclones are remarkably consistent in System III longitude.
… 
The poles of Jupiter as they appear at visible and infrared wavelengths Projected maps of the regions surrounding the north pole (top) and south pole (bottom) from the JIRAM 5-μm M-filter observations (right panels) and JunoCam colour-composite images (left panels) during PJ4 on 2 February 2017. The latitude circle is 80° N or 80° S (planetocentric). Meridians are drawn every 15° of longitude, and 0° W in System III is positioned at the centre right of the images. By operating at thermal-infrared wavelengths, JIRAM observes the atmospheric structures regardless of solar illumination, whereas JunoCam’s optical images are restricted to only the illuminated hemisphere, which is why only part of the JunoCam map for the north pole is present. JIRAM radiance, ranging from 0.02 W m⁻² sr⁻¹ (dark red) to 0.8 W m⁻² sr⁻¹ (white) is corrected with respect to the emission angle; the radiance scale is logarithmic. The JunoCam images are corrected with respect to solar illumination angle, as discussed in ref. 5 and the colours of the maps have been stretched and balanced to enhance atmospheric features. Cyclonic features can be seen clustered around each pole with regular circular shapes, some with spiral arms. For the south polar region, we note that there is a wider longitude separation (a ‘gap’) between the cyclones near 180° W (centre left side) than between the other cyclones. Two smaller cold (dark red) features can be seen to the upper left of the NPC, which are anticyclonic vortices. PowerPoint slide
The poles of Jupiter as they appear at visible and infrared wavelengths Projected maps of the regions surrounding the north pole (top) and south pole (bottom) from the JIRAM 5-μm M-filter observations (right panels) and JunoCam colour-composite images (left panels) during PJ4 on 2 February 2017. The latitude circle is 80° N or 80° S (planetocentric). Meridians are drawn every 15° of longitude, and 0° W in System III is positioned at the centre right of the images. By operating at thermal-infrared wavelengths, JIRAM observes the atmospheric structures regardless of solar illumination, whereas JunoCam’s optical images are restricted to only the illuminated hemisphere, which is why only part of the JunoCam map for the north pole is present. JIRAM radiance, ranging from 0.02 W m⁻² sr⁻¹ (dark red) to 0.8 W m⁻² sr⁻¹ (white) is corrected with respect to the emission angle; the radiance scale is logarithmic. The JunoCam images are corrected with respect to solar illumination angle, as discussed in ref. 5 and the colours of the maps have been stretched and balanced to enhance atmospheric features. Cyclonic features can be seen clustered around each pole with regular circular shapes, some with spiral arms. For the south polar region, we note that there is a wider longitude separation (a ‘gap’) between the cyclones near 180° W (centre left side) than between the other cyclones. Two smaller cold (dark red) features can be seen to the upper left of the NPC, which are anticyclonic vortices. PowerPoint slide
… 
The poles observed by JunoCam during the first four passes at Jupiter A composite is shown of the polar regions observed by JunoCam not only during PJ4 but also at complementary longitudes, acquired during PJ1, PJ3 and PJ5 for regions not illuminated by sunlight during PJ4. The PJ4 projection has been preserved as in the left panels in Fig. 1; the remainder of the unfilled space is covered by a composite of images from the other perijove passes. The remaining regions that are dark in the left panels of Fig. 1 are a smooth composite of JunoCam images taken during PJ1, PJ3 and PJ5. The area in the centre of the north polar region (left panel) is dark because those latitudes were not illuminated. Elsewhere on Jupiter, cyclonic circulations assume various forms, especially at high latitudes, but none is a simple spiral with a circular outline, except for some very small ones. We note that, although they were imaged 53–106 days (1–2 Juno orbits) from the PJ4 observations, the positions and even the gross morphologies of the cyclones imaged during those orbits are not very different from their overall morphology in the PJ4 JIRAM map. The JunoCam map colours were chosen to enhance atmospheric features. PowerPoint slide
The poles observed by JunoCam during the first four passes at Jupiter A composite is shown of the polar regions observed by JunoCam not only during PJ4 but also at complementary longitudes, acquired during PJ1, PJ3 and PJ5 for regions not illuminated by sunlight during PJ4. The PJ4 projection has been preserved as in the left panels in Fig. 1; the remainder of the unfilled space is covered by a composite of images from the other perijove passes. The remaining regions that are dark in the left panels of Fig. 1 are a smooth composite of JunoCam images taken during PJ1, PJ3 and PJ5. The area in the centre of the north polar region (left panel) is dark because those latitudes were not illuminated. Elsewhere on Jupiter, cyclonic circulations assume various forms, especially at high latitudes, but none is a simple spiral with a circular outline, except for some very small ones. We note that, although they were imaged 53–106 days (1–2 Juno orbits) from the PJ4 observations, the positions and even the gross morphologies of the cyclones imaged during those orbits are not very different from their overall morphology in the PJ4 JIRAM map. The JunoCam map colours were chosen to enhance atmospheric features. PowerPoint slide
… 
High-resolution view of the polar vortices The left panel shows the north pole as seen in the 5-μm spectral region (JIRAM M-filter) at an average spatial resolution of 18 km per pixel. The right panel shows the south pole at an average spatial resolution of 25 km per pixel in the same filter. These maps represent the highest available spatial resolution of JIRAM images during PJ4. The red colour scale from black to white is associated with the apparent brightness temperature shown, covering 190–260 K. Some cyclones look more clearly structured with alternating cold (cloudier) and warm (clearer) banding as a function of radius. It also clearly depicts the mesoscale dynamics over Jupiter’s polar regions, showing a chaotic environment with many wavy structures and smaller anticyclones and cyclones developing among the largest ones. Such small anticyclonic eddies can be seen between some of the cyclones, especially around the NPC, where the largest of them measures about 1,200 km in diameter. There is a great structural difference between the NPC, which is dominated by a very small-scale cloud structure, and the SPC, which is characterized by a quasi-laminar behaviour. The SPC has a diameter of about 5,800 km and its centre is very peculiar, presenting an elongated ‘eye’ shape instead of the circular structure characterizing the centre of all of the other cyclones. PowerPoint slide
High-resolution view of the polar vortices The left panel shows the north pole as seen in the 5-μm spectral region (JIRAM M-filter) at an average spatial resolution of 18 km per pixel. The right panel shows the south pole at an average spatial resolution of 25 km per pixel in the same filter. These maps represent the highest available spatial resolution of JIRAM images during PJ4. The red colour scale from black to white is associated with the apparent brightness temperature shown, covering 190–260 K. Some cyclones look more clearly structured with alternating cold (cloudier) and warm (clearer) banding as a function of radius. It also clearly depicts the mesoscale dynamics over Jupiter’s polar regions, showing a chaotic environment with many wavy structures and smaller anticyclones and cyclones developing among the largest ones. Such small anticyclonic eddies can be seen between some of the cyclones, especially around the NPC, where the largest of them measures about 1,200 km in diameter. There is a great structural difference between the NPC, which is dominated by a very small-scale cloud structure, and the SPC, which is characterized by a quasi-laminar behaviour. The SPC has a diameter of about 5,800 km and its centre is very peculiar, presenting an elongated ‘eye’ shape instead of the circular structure characterizing the centre of all of the other cyclones. PowerPoint slide
… 
Figures - available from: Nature
This content is subject to copyright. Terms and conditions apply.
A preview of this full-text is provided by Springer Nature.
Learn more
Content available from Nature
This content is subject to copyright. Terms and conditions apply.
216 | NATURE | VOL 555 | 8 MARCH 2018
LETTER doi:10.1038/nature25491
Clusters of cyclones encircling Jupiter’s poles
A. Adriani1, A. Mura1, G. Orton2, C. Hansen3, F. Altieri1, M. L. Moriconi4, J. Rogers5, G. Eichstädt6, T. Momary2, A. P. Ingersoll7,
G. Filacchione1, G. Sindoni1, F. Tabataba-Vakili2, B. M. Dinelli4, F. Fabiano4,8, S. J. Bolton9, J. E. P. Connerney10, S. K. Atreya11,
J. I. Lunine12, F. Tosi1, A. Migliorini1, D. Grassi1, G. Piccioni1, R. Noschese1, A. Cicchetti1, C. Plainaki13, A. Olivieri13, M. E. O’Neill14,
D. Turrini1,15, S. Stefani1, R. Sordini1 & M. Amoroso13
The familiar axisymmetric zones and belts that characterize
Jupiter’s weather system at lower latitudes give way to pervasive
cyclonic activity at higher latitudes
1
. Two-dimensional turbulence
in combination with the Coriolis β-effect (that is, the large
meridionally varying Coriolis force on the giant planets of the Solar
System) produces alternating zonal flows
2
. The zonal flows weaken
with rising latitude so that a transition between equatorial jets and
polar turbulence on Jupiter can occur
3,4
. Simulations with shallow-
water models of giant planets support this transition by producing
both alternating flows near the equator and circumpolar cyclones
near the poles5–9. Jovian polar regions are not visible from Earth
owing to Jupiter’s low axial tilt, and were poorly characterized by
previous missions because the trajectories of these missions did
not venture far from Jupiter’s equatorial plane. Here we report
that visible and infrared images obtained from above each pole
by the Juno spacecraft during its first five orbits reveal persistent
polygonal patterns of large cyclones. In the north, eight circumpolar
cyclones are observed about a single polar cyclone; in the south, one
polar cyclone is encircled by five circumpolar cyclones. Cyclonic
circulation is established via time-lapse imagery obtained over
intervals ranging from 20 minutes to 4 hours. Although migration of
cyclones towards the pole might be expected as a consequence of the
Coriolis β-effect, by which cyclonic vortices naturally drift towards
the rotational pole, the configuration of the cyclones is without
precedent on other planets (including Saturn’s polar hexagonal
features). The manner in which the cyclones persist without merging
and the process by which they evolve to their current configuration
are unknown.
NASA’s Juno spacecraft10,11 has been operating in a 53-day highly
elliptical polar orbit of Jupiter since 5 July 2016. The spacecraft has
passed close to Jupiter six times now, on five of which occasions
instruments on board were able to sound the planet and observe
many interesting atmospheric structures12–15. The Juno spacecraft is
in a high-inclination orbit with perijove (the point in its orbit nearest
Jupiter’s centre) approximately 4,000 km above the cloud tops, passing
from pole to equator to pole in about two hours. From their unique
vantage point above the poles, JIRAM
16,17
(Jupiter InfraRed Auroral
Mapper) and JunoCam18, onboard Juno, obtained unprecedented
views of Jupiter’s polar regions. JIRAM is an infrared imager suitable
for atmospheric mapping and JunoCam is a pushframe visible camera.
Jupiter fly-bys took place during perijove passes PJ1 on 28 August
2016, PJ3 on 11 December 2016, PJ4 on 2 February 2017 and PJ5
on 27 March 2017 (no remote-sensing observations were collected
during PJ2).
The atmospheric structure in Jupiter’s polar regions is very different
from the well known axisymmetric banding of alternating belts and
zones at lower latitudes. The polar turbulence predicted by models is
consistent with initial close-up observations in the visible part of the
spectrum
15
. Cyclones, as opposed to anticyclones, were expected in
the polar regions as a result of the Coriolis β -effect9,19,20. What was
unexpected is their stable appearance, close clustering and symmetry
around each of the poles.
The Northern Polar Cyclone (NPC, Fig. 1) has a diameter of approxi-
mately 4,000 km (on the JIRAM infrared images). It is offset relative to
the geographic north pole of Jupiter by about 0.5° and is surrounded by
eight circumpolar cyclones (henceforth referred to as just ‘cyclones’) in
a double-squared geometric pattern (Figs 1 and 2). Counting alternat-
ing cyclones, four are centred at about 83.3°N and the other four are
centred at about 82.5°N. The square formed by the latter four cyclones
is shifted with respect to the square formed by the former four cyclones
by 45° longitude, forming a ‘ditetragonal’ shape, in which the angular
distances between the centre of one cyclone and the next vary from 43°
to 47°. All cyclones have similar dimensions with diameters ranging
from 4,000 km to 4,600 km. Spiral arms are prominent in their outer
regions, but tend to disappear in their inner regions except in the NPC
itself. These arms define an additional sphere of influence beyond the
cores of the cyclones in which co-rotating material can be found. The
four cyclones furthest from the NPC have broad cloud-covered inner
regions with sharp oblate boundaries. The four cyclones interspersed
between them have more diverse and irregular inner regions, with very
small-scale cloud textures; some of them appear chaotic and turbulent.
The Southern Polar Cyclone (SPC, Figs 1 and 2) is surrounded by
five large circumpolar cyclones in a quasi-pentagonal pattern. They
are of similar size, but are generally bigger than the northern cyclones,
with diameters ranging between 5,600 km and 7,000 km. The southern
cyclones present a range of morphologies, although the differences are
much less distinct than in the north. In particular, some of them display
a quasi-laminar circulation: the SPC and two adjacent cyclones have
cloud spirals converging to the centre, while the other three cyclones
appear to be very turbulent along their spiral cloud branches. The SPC
has an offset of about 1°–2° relative to the geographic south pole and
the angular distance between two adjacent cyclones is not as regular as
in the north: it can vary from 65° to 80° relative to the centre of rotation
of the SPC.
Figures 1 and 2 show the correspondence between the features in
JIRAM maps and in JunoCam images. Regions that are relatively bright
in the JunoCam images are cool in the JIRAM thermal infrared images
and regions that are relatively dark in the visible are warm. Because the
JIRAM thermal radiance in the approximately 5-μ m M-band is primarily
governed by cloud opacity, regions that appear warm can be interpreted
as relatively clear of clouds, allowing radiance from deeper, warmer
regions to be detected, and regions that appear cold must be cloudier.
1INAF-Istituto di Astrofisica e Planetologia Spaziali, Roma, Italy. 2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA. 3Planetary Science Institute, Tucson,
Arizona, USA. 4CNR-Istituto di Scienze dell’Atmosfera e del Clima, Bologna e Roma, Italy. 5British Astronomical Association, Burlington House, Piccadilly, London W1J 0DU, UK. 6Alexanderstraße
21, 70184 Stuttgart, Germany. 7Division of Geology and Planetary Sciences, California Institute of Technology, Pasadena, California, USA. 8Dipartimento di Fisica e Astronomia, Università di
Bologna, Bologna, Italy. 9Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA. 10Code 695, NASA/Goddard Space Flight Center, Greenbelt, Maryland,
USA. 11Planetary Sciences Laboratory, University of Michigan, Ann Arbor, Michigan, USA. 12Center for Astrophysics and Space Science, Cornell University, Ithaca, New York, USA. 13Agenzia Spaziale
Italiana, Roma, Italy. 14Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois, USA. 15Departamento de Fisica, Universidad de Atacama, Copayapu 485, Copiapò, Chile.
© 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
... The Juno mission has unveiled intriguing polygonal patterns of closely packed large-scale cyclones on Jupiter's poles (Adriani et al., 2018;Tabataba-Vakili et al., 2020). This discovery of closely packed polar vortices poses a challenging problem in comprehending the dynamics of the Jovian atmosphere. ...
Examination of Vorticity and Divergence on a Rotating Turbulent Convection Model of Jupiter's Polar Vortices
Article
Full-text available
  • May 2024
The correlation between divergence and vorticity has traditionally served as a signature of convection in rotating fluids. While this correlation has been observed in the JIRAM brightness temperature data for Jupiter's polar vortices, it is notably absent in the JIRAM images. This discrepancy presents a new challenge in determining whether this correlation can serve as a reliable signature of convection in rapidly rotating atmospheres. In this study, we analyzed data from a three‐dimensional simulation of Jupiter's polar vortices using a deep convection model. Our findings confirm the theoretical prediction of a negative correlation between divergence and vorticity in the northern hemisphere. Interestingly, this correlation is weaker within the cyclones compared to outside them. The skewness of upflows and downflows plays an important role in this negative correlation. We also observed that the correlation varies with height, being strongest near the interface and decaying away from it. The correlation diminishes when the resolution is reduced. Furthermore, our findings suggest that the geostrophic approximation may not be suitable for the Jovian atmosphere, particularly in the stable layer. Both tilting and stretching effects contribute to the material derivative of vorticity, with the tilting effect dominating in the unstable layer and the stretching effect prevailing in the stable layer. This suggests a transfer of vorticity from the convectively unstable layer to the stable layer. Consistent with observations, we also noted an upscale energy transfer from smaller to larger scales.
View
Frontogenesis at Jovian high latitudes
Article
Full-text available
  • Jun 2024
  • NAT PHYS
Frontogenesis is the process by which fronts, separating fluids of different temperatures, are generated in the terrestrial atmosphere and oceans. It is of interest to consider whether this process appears in other planetary atmospheres. Here we analyse infra-red images taken by the Juno spacecraft at the Jovian poles and reveal ubiquitous vortices with a diameter of hundreds to thousands of kilometres and filaments with a width of tens of kilometres embedded in between the vortices. Our analysis shows that the filaments are dynamically active, reminiscent of terrestrial frontogenesis. Furthermore, our results indicate that Jovian frontogenesis acts in concert with moist convection, with the former mechanism favouring the development of cyclones and the latter the development of anti-cyclones. Even though moist convection is the main driver, frontogenesis accounts for a quarter of the total transfer of potential to kinetic energy, enhancing the upscale transfer of energy to larger vortices. Frontogenesis contributes 40% to the vertical heat transport, efficiently redistributing heat from Jupiter’s interior to its tropopause. This study highlights the broad range of interacting scales from tens to thousands of kilometres and the diverse physical mechanisms active at Jovian high latitudes.
View
View
From a vortex gas to a vortex crystal in instability-driven two-dimensional turbulence
Article
  • Apr 2024
We study structure formation in two-dimensional turbulence driven by an external force, interpolating between linear instability forcing and random stirring, subject to nonlinear damping. Using extensive direct numerical simulations, we uncover a rich parameter space featuring four distinct branches of stationary solutions: large-scale vortices, hybrid states with embedded shielded vortices (SVs) of either sign, and two states composed of many similar SVs. Of the latter, the first is a dense vortex gas where all SVs have the same sign and diffuse across the domain. The second is a hexagonal vortex crystal forming from this gas when the linear instability is sufficiently weak. These solutions coexist stably over a wide parameter range. The late-time evolution of the system from small-amplitude initial conditions is nearly self-similar, involving three phases: initial inverse cascade, random nucleation of SVs from turbulence and, once a critical number of vortices is reached, a phase of explosive nucleation of SVs, leading to a statistically stationary state. The vortex gas is continued in the forcing parameter, revealing a sharp transition towards the crystal state as the forcing strength decreases. This transition is analysed in terms of the diffusivity of individual vortices using ideas from statistical physics. The crystal can also decay via an inverse cascade resulting from the breakdown of shielding or insufficient nonlinear damping acting on SVs. Our study highlights the importance of the forcing details in two-dimensional turbulence and reveals the presence of non-trivial SV states in this system, specifically the emergence and melting of a vortex crystal.
View
Moons and Jupiter Imaging Spectrometer (MAJIS) on Jupiter Icy Moons Explorer (JUICE)
Article
Full-text available
  • Mar 2024
  • SPACE SCI REV
The MAJIS (Moons And Jupiter Imaging Spectrometer) instrument on board the ESA JUICE (JUpiter ICy moon Explorer) mission is an imaging spectrometer operating in the visible and near-infrared spectral range from 0.50 to 5.55 μm in two spectral channels with a boundary at 2.3 μm and spectral samplings for the VISNIR and IR channels better than 4 nm/band and 7 nm/band, respectively. The IFOV is 150 μrad over a total of 400 pixels. As already amply demonstrated by the past and present operative planetary space missions, an imaging spectrometer of this type can span a wide range of scientific objectives, from the surface through the atmosphere and exosphere. MAJIS is then perfectly suitable for a comprehensive study of the icy satellites, with particular emphasis on Ganymede, the Jupiter atmosphere, including its aurorae and the spectral characterization of the whole Jupiter system, including the ring system, small inner moons, and targets of opportunity whenever feasible. The accurate measurement of radiance from the different targets, in some case particularly faint due to strong absorption features, requires a very sensitive cryogenic instrument operating in a severe radiation environment. In this respect MAJIS is the state-of-the-art imaging spectrometer devoted to these objectives in the outer Solar System and its passive cooling system without cryocoolers makes it potentially robust for a long-life mission as JUICE is. In this paper we report the scientific objectives, discuss the design of the instrument including its complex on-board pipeline, highlight the achieved performance, and address the observation plan with the relevant instrument modes.
View
Quasi-two-dimensional turbulence
Article
  • Nov 2023
Many fluid-dynamical systems met in nature are quasi-two-dimensional: they are constrained to evolve in approximately two dimensions with little or no variation along the third direction. This has a drastic effect in the flow evolution because the properties of three-dimensional turbulence are fundamentally different from those of two-dimensional turbulence. In three dimensions, energy is transferred on average towards small scales, while in two dimensions, energy is transferred towards large scales. Quasi-two-dimensional flows thus stand in a crossroad, with two-dimensional motions attempting to self-organize and generate large scales while three-dimensional perturbations cause disorder, disrupting any large-scale organization. Where is energy transferred in such systems? It has been realized recently that in fact the two behaviors can coexist with a simultaneous transfer of energy both to large and to small scales. How the cascade properties change as the variations along the third direction are suppressed has led to discovery of different regimes or phases of turbulence of unexpected richness in behavior. Here, recent discoveries on such systems are reviewed. It is described how the transition from three-dimensional to two-dimensional flows takes place, the different phases of turbulence met and the nature of the transitions from one phase to the other. Finally, the implications these new discoveries have on different physical systems are discussed.
View
Gas Giant Simulations of Eddy‐Driven Jets Accompanied by Deep Meridional Circulation
Article
  • Oct 2023
Jupiter's atmosphere comprises several dynamical regimes: the equatorial eastward flows and surrounding retrograde jets; the midlatitudes, with the eddy‐driven, alternating jet‐streams and meridional circulation cells; and the jet‐free turbulent polar region. Despite intensive research conducted on each of these dynamical regimes over the past decades, they remain only partially understood. Saturn's atmosphere also encompasses similar distinguishable regimes, but observational evidence for midlatitude deep meridional cells is lacking. Models offer a variety of explanations for each of these regions, but only a few are capable of simulating more than one of the regimes at once. This study presents new numerical simulations using a 3D deep anelastic model that can reproduce the equatorial flows as well as the midlatitudinal pattern of the mostly barotropic, alternating eddy‐driven jets and the meridional circulation cells accompanying them. These simulations are consistent with recent Juno mission gravity and microwave data. We find that the vertical eddy momentum fluxes are as important as the meridional eddy momentum fluxes, which drive the midlatitudinal circulation on Earth. In addition, we discuss the parameters controlling the number of midlatitudinal jets/cells, their extent, strength, and location. We identify the strong relationship between meridional circulation and the zonal jets in a deep convection setup, and analyze the mechanism responsible for their generation and maintenance. The analysis presented here provides another step in the ongoing pursuit of understanding the deep atmospheres of gas giants.
View
Observational evidence for cylindrically oriented zonal flows on Jupiter
Article
Full-text available
  • Oct 2023
  • Nat. Astron.
The atmospheric dynamics of Jupiter are dominated by strong zonal winds engulfing the planet. Since the first gravity measurements taken by Juno at Jupiter, the low-degree gravity harmonics (J3–J10) have been used to determine the depth and structure of the zonal winds observed at the cloud level, limiting inferences on the deep flows to the wide latitudinal structure of these harmonics. Here, using constraints on the dynamical contribution to gravity at high latitude, we present the gravity harmonics up to J40. We find an excellent correlation between these measurements and the gravity harmonics resulting from the observed cloud-level winds extending inwards cylindrically to depths of ~10⁵ bar (3,000 km). These measurements provide direct evidence that the flows penetrate inwards along the direction of the spin axis, confirming the cylindrical nature of the flow, which has been postulated theoretically since the 1970s. Furthermore, this detailed new gravity spectrum allows us to quantify the contribution of the various jets to the gravity signal, showing the dominance of the strong zonal flows around 20° latitude in both hemispheres.
View
Two-dimensional turbulence above topography: Vortices and potential vorticity homogenization
Article
  • Oct 2023
The evolution of unforced and weakly damped two-dimensional turbulence over random rough topography presents two extreme states. If the initial kinetic energy E is sufficiently high, then the topography is a weak perturbation, and evolution is determined by the spontaneous formation and mutual interaction of coherent axisymmetric vortices. High-energy vortices roam throughout the domain and mix the background potential vorticity (PV) to homogeneity, i.e., in the region between vortices, which is most of the domain, the relative vorticity largely cancels the topographic PV. If E is low, then vortices still form but they soon become locked to topographic features: Anticyclones sit above topographic depressions and cyclones above elevated regions. In the low-energy case, with topographically locked vortices, the background PV retains some spatial variation. We develop a unified framework of topographic turbulence spanning these two extreme states of low and high energy. A main organizing concept is that PV homogenization demands a particular kinetic energy level E ♯ . E ♯ is the separator between high-energy evolution and low-energy evolution.
View
The Dynamics of Jupiter's and Saturn's Weather Layers: A Synthesis After Cassini and Juno
Article
  • Oct 2023
Until recently, observations of the giant planets of our Solar System were confined to sampling relatively shallow regions of their atmospheres, leaving many uncertainties as to the dynamics of deeper layers. The Cassini and Juno missions to Saturn and Jupiter, however, have begun to address these issues, for example, by measuring their gravity and magnetic fields. The results show that the zonally coherent jets and cloud bands extend to levels where the electrical conductivity of the fluid becomes significant, whereas large-scale vortices, such as the Great Red Spot, are relatively shallow but may have deep-seated roots. The polar regions also exhibit intense cyclonic vortices that, on Jupiter, arrange themselves into remarkably regular “vortex crystals.” Numerical models seem able to capture some of this complexity, but many issues remain unresolved, suggesting a need for models that can represent both deep and shallow processes sufficiently realistic ally to compare with observations. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 56 is January 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
View
The first close-up images of Jupiter's polar regions: Results from the Juno mission JunoCam instrument: JunoCam Images of Jupiter's Poles
Article
Full-text available
  • May 2017
During Juno's first perijove encounter, the JunoCam instrument acquired the first images of Jupiter's polar regions at 50–70 km spatial scale at low emission angles. Poleward of 64–68° planetocentric latitude, where Jupiter's east-west banded structure breaks down, several types of discrete features appear on a darker background. Cyclonic oval features are clustered near both poles. Other oval-shaped features are also present, ranging in size from 2000 km down to JunoCam's resolution limits. The largest and brightest features often have chaotic shapes. Two narrow linear features in the north, associated with an overlying haze feature, traverse tens of degrees of longitude. JunoCam also detected an optically thin cloud or haze layer past the northern nightside terminator estimated to be 58 ± 21 km (approximately three scale heights) above the main cloud deck. JunoCam will acquire polar images on every perijove, allowing us to track the state and evolution of longer-lived features.
View
View
Multiple-wavelength sensing of Jupiter during the Juno mission's first perijove passage: Multiple-Wavelength Sensing of Jupiter
Article
  • May 2017
We compare Jupiter observations made around 27 August 2016 by Juno's JunoCam, Jovian Infrared Auroral Mapper (JIRAM), MicroWave Radiometer (MWR) instruments, and NASA's Infrared Telescope Facility. Visibly dark regions are highly correlated with bright areas at 5 µm, a wavelength sensitive to gaseous NH3 gas and particulate opacity at p ≤5 bars. A general correlation between 5-µm and microwave radiances arises from a similar dependence on NH3 opacity. Significant exceptions are present and probably arise from additional particulate opacity at 5 µm. JIRAM spectroscopy and the MWR derive consistent 5-bar NH3 abundances that are within the lower bounds of Galileo measurement uncertainties. Vigorous upward vertical transport near the equator is likely responsible for high NH3 abundances and with enhanced abundances of some disequilibrium species used as indirect indicators of vertical motions.
View
Characterization of the white ovals on Jupiter's southern hemisphere using the first data by the Juno/JIRAM instrument: JUPITER OVALS AS SEEN BY JIRAM/JUNO
Article
  • May 2017
During the first perijove passage of the Juno mission, the Jovian InfraRed Auroral Mapper (JIRAM) observed a line of closely spaced oval features in Jupiter's southern hemisphere, between 30°S and 45°S. In this work, we focused on the longitudinal region covering the three ovals having higher contrast at 5 μm, i.e., between 120°W and 60°W in System III coordinates. We used the JIRAM's full spectral capability in the range 2.4–3 μm together with a Bayesian data inversion approach to retrieve maps of column densities and altitudes for an NH3 cloud and an N2H4 haze. The deep (under the saturation level) volume mixing ratio and the relative humidity for gaseous ammonia were also retrieved. Our results suggest different vortex activity for the three ovals. Updraft and downdraft together with considerations about the ammonia condensation could explain our maps providing evidences of cyclonic and anticyclonic structures.
View
Preliminary results on the composition of Jupiter's troposphere in hot spot regions from the JIRAM/Juno instrument: Jupiter Hot Spots as Seen by JIRAM/Juno
Article
  • May 2017
The Jupiter InfraRed Auroral Mapper (JIRAM) instrument on board the Juno spacecraft performed observations of two bright Jupiter hot spots around the time of the first Juno pericenter passage on 27 August 2016. The spectra acquired in the 4–5 µm spectral range were analyzed to infer the residual opacities of the uppermost cloud deck as well as the mean mixing ratios of water, ammonia, and phosphine at the approximate level of few bars. Our results support the current view of hot spots as regions of prevailing descending vertical motions in the atmosphere but extend this view suggesting that upwelling may occur at the southern boundaries of these structures. Comparison with the global ammonia abundance measured by Juno Microwave Radiometer suggests also that hot spots may represent sites of local enrichment of this gas. JIRAM also identifies similar spatial patterns in water and phosphine contents in the two hot spots.
View
Jupiter’s magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits
Article
  • May 2017
Juno swoops around giant Jupiter Jupiter is the largest and most massive planet in our solar system. NASA's Juno spacecraft arrived at Jupiter on 4 July 2016 and made its first close pass on 27 August 2016. Bolton et al. present results from Juno's flight just above the cloud tops, including images of weather in the polar regions and measurements of the magnetic and gravitational fields. Juno also used microwaves to peer below the visible surface, spotting gas welling up from the deep interior. Connerney et al. measured Jupiter's aurorae and plasma environment, both as Juno approached the planet and during its first close orbit. Science , this issue p. 821 , p. 826
View
Jupiter's interior and deep atmosphere: The initial pole-To-pole passes with the Juno spacecraft
Article
  • May 2017
Juno swoops around giant Jupiter Jupiter is the largest and most massive planet in our solar system. NASA's Juno spacecraft arrived at Jupiter on 4 July 2016 and made its first close pass on 27 August 2016. Bolton et al. present results from Juno's flight just above the cloud tops, including images of weather in the polar regions and measurements of the magnetic and gravitational fields. Juno also used microwaves to peer below the visible surface, spotting gas welling up from the deep interior. Connerney et al. measured Jupiter's aurorae and plasma environment, both as Juno approached the planet and during its first close orbit. Science , this issue p. 821 , p. 826
View
Juno’s Earth flyby: the Jovian infrared Auroral Mapper preliminary results
Article
  • Aug 2016
The Jovian InfraRed Auroral Mapper, JIRAM, is an image-spectrometer onboard the NASA Juno spacecraft flying to Jupiter. The instrument has been designed to study the aurora and the atmosphere of the planet in the spectral range 2–5 μm. The very first scientific observation taken with the instrument was at the Moon just before Juno’s Earth fly-by occurred on October 9, 2013. The purpose was to check the instrument regular operation modes and to optimize the instrumental performances. The testing activity will be completed with pointing and a radiometric/spectral calibrations shortly after Jupiter Orbit Insertion. Then the reconstruction of some Moon infrared images, together with co-located spectra used to retrieve the lunar surface temperature, is a fundamental step in the instrument operation tuning. The main scope of this article is to serve as a reference to future users of the JIRAM datasets after public release with the NASA Planetary Data System.
View
Polar vortex formation in giant planet atmospheres under moist convection
Article
  • Dec 2014
A strong cyclonic vortex has been observed on each of Saturn’s poles, coincident with a local maximum in observed tropospheric temperature. Neptune also exhibits a relatively warm, although much more transient, region on its south pole. Whether similar features exist on Jupiter will be resolved by the 2016 Juno mission. Energetic, small-scale storm-like features that originate from the water-cloud level or lower have been observed on each of the giant planets and attributed to moist convection, suggesting that these storms play a significant role in global heat transfer from the hot interior to space. Nevertheless, the creation and maintenance of Saturn’s polar vortices, and their presence or absence on the other giant planets, are not understood. Here we use simulations with a shallow-water model to show that storm generation, driven by moist convection, can create a strong polar cyclone throughout the depth of a planet’s troposphere. We find that the type of shallow polar flow that occurs on a giant planet can be described by the size ratio of small eddies to the planetary radius and the energy density of its atmosphere due to latent heating from moist convection. We suggest that the observed difference in these parameters between Saturn and Jupiter may preclude a Jovian polar cyclone.
View
Corrigendum: Polar vortex formation in giant-planet atmospheres due to moist convection
Article
  • Oct 2015
A strong cyclonic vortex has been observed on each of Saturn's poles, coincident with a local maximum in observed tropospheric temperature(1-3). Neptune also exhibits a relatively warm, although much more transient(4), region on its south pol. Whether similar features exist on Jupiter will be resolved by the 2016 Juno mission. Energetic, small-scale storm-like features that originate from the water-cloud level or lower have been observed on each of the giant planets and attributed to moist convection, suggesting that these storms play a significant role in global heat transfer from the hot interior to space. Nevertheless, the creation and maintenance of Saturn's polar vortices, and their presence or absence on the other giant planets, are not understood. Here we use simulations with a shallow-water model to show that storm generation, driven by moist convection, can create a strong polar cyclone throughout the depth of a planet's troposphere. We find that the type of shallow polar flow that occurs on a giant planet can be described by the size ratio of small eddies to the planetary radius and the energy density of its atmosphere due to latent heating from moist convection. We suggest that the observed difference in these parameters between Saturn and Jupiter may preclude a jovian polar cyclone.
View