Clusters of Cyclones Encircling Jupiter's Poles

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Abstract
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.
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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.
… 
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
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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.
NASAs 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
Jupiters 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 Jupiters 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.
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Letter reSeArCH
8 MARCH 2018 | VOL 555 | NATURE | 217
Thus, the visibly bright discrete features in the JunoCam images in Figs 1
and 2 correspond to high-altitude clouds, while the darker background
corresponds to a deeper cloud deck. This corresponds to a general qual-
itative result from JunoCam observations made during PJ1, that visually
bright regions correspond to regions that are also relatively bright in the
890-nm band, which is sensitive to absorption by methane gas, implying
high-altitude clouds in those regions
14
. Figure 3, with the highest-resolu-
tion maps of the polar regions, gives a detailed view of the polar morphol-
ogies, showing JIRAM images corresponding to brightness temperatures
in the range 190–260 K.
In most cases, the cyclones are essentially in contact if the spiral
arms that extend beyond the core are included. In some cases, a single
5,000 km
5,000 km
Figure 1 | 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-μ m 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m2sr1 (dark red) to 0.8Wm2sr1
(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.
South poleNorth pole
Figure 2 | 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.
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Content courtesy of Springer Nature, terms of use apply. Rights reserved
Letter
reSeArCH
218 | NATURE | VOL 555 | 8 MARCH 2018
cloud streak connects the outer spiral arms of adjacent cyclones and
can be seen to be continuously stretched. The SPC is in contact with
the five cyclones around it. By contrast, the PJ4 JIRAM animation (see
Supplementary Videos) reveals a chaotic zone between the NPC and
the eight surrounding cyclones, within which there is a largely con-
tinuous westward (clockwise) flow at about 86°N; poleward of this,
the eastward (anticlockwise) flow of the NPC begins. This chaotic
zone appears to contain turbulent small-scale cloud textures and a
few small anticyclonic vortices. The largest of these, located between
the NPC and the cyclones, may be identical to a similar anticyclonic
vortex at PJ5, having moved westward by 31° longitude in Juno’s 53-day
orbital period. JIRAM data acquired during PJ4 cover a time span
of about 2 h at each pole, enabling us to monitor the movements of
the clouds and other structures that are evident within each cyclone,
which in turn permits the identification of cyclonic and anticyclonic
zones. The velocity field inside each cyclone is not straightforward
to evaluate from these data, both because the pointing inaccuracy of
JIRAM is not negligible when dealing with fine-scale structures inside
cyclones, and because detailed structures whose movement is visible
are not scattered uniformly. Table 1 provides a summary of preliminary
JIRAM measurements of the rotational speeds of individual cyclones
at 1,500 km from their respective centres.
The changes occurring in the polar polygons can be seen by the
JIRAM observations with a time lapse of about 53 terrestrial days
between PJ4 and PJ5 (Extended Data Fig. 1). By this analysis, the
northern eight cyclones appear to drift very slowly around the north
pole (or around the NPC), by approximately 2.6° eastward in System
III longitude. The changes between the observations taken by JunoCam
are based on images of the sunlit side of the poles during PJ1, PJ3, PJ4
and PJ5. On the other hand, JunoCam polar images have an overlap of
about 90°–180° in sunlit longitudes between successive perijove obser-
vations in similar 53-day intervals, and can also be compared with the
complete map from JIRAM at PJ4. They show that the eight cyclones
are preserved throughout the entire seven-month period, retaining
their individual morphological characteristics, and showing only minor
movements (Fig. 2). The visible sector of the octagon rotated around
the north pole as follows (positive is westward): PJ1 to PJ3, about
+ 2°; PJ3 to PJ4, to 7.5°; PJ4 to PJ5, 0° to 3.5°. Thus the octagon
has not shown any progressive rotation about the pole in System III
longitudes. Both instruments observe small meridional displacements
260 K
246 K
232 K
218 K
204 K
190 K
Figure 3 | High-resolution view of the polar
vortices. The left panel shows the north pole
as seen in the 5-μ m 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.
Table 1 | Spin velocities of the single cyclones
North pole South pole
Circumpolar
cyclone number
Angular velocity
(degmin1)
Tangent velocity
(kmh1)
Full rotation
hours
Circumpolar
cyclone number
Angular velocity
(degmin1)
Tangent velocity
(kmh1)
Full rotation
hours
NPC 0.17 267 35.3 SPC 0.19 299 31.6
10.22 343 27.5 1 (H) 0.13 204 46.1
3 (D) 0.21 337 28.0 20.17 273 34.5
4 (E) 0.10 157 60.0 30.16 252 37.5
5 (F) 0.12 296 48.0 40.21 330 28.6
60.19 295 32.0 5 (G) 0.17 273 34.5
70.22 354 26.6
80.12 296 48.0
Spin velocities were calculated at the radial distance of approximately 1,500 km from the spinning centres during PJ4 by JIRAM images. There were not enough data to compute the velocity of northern
circumpolar cyclone 2. The numbering of the northern circumpolar cyclones goes from 1 to 8 proceeding anticlockwise, with circumpolar cyclone 1 the one located at 0° longitude. The numbering of
the southern circumpolar cyclones starts from the circumpolar cyclone at 150° longitude and proceeds anticlockwise. Letters in parentheses identify the circumpolar cyclone, if present, in Extended
Data Fig. 1. A quick calculation assuming the gradient wind balance, which includes Coriolis, centrifugal and pressure forces, indicates pressure gradients of about 5–10Pakm1 at 1,500 km from the
circumpolar cyclone centres.
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Letter reSeArCH
8 MARCH 2018 | VOL 555 | NATURE | 219
of individual cyclones of the same order of magnitude. For the cyclones
at the south pole, JunoCam comparisons between perijove passes do
suggest a progressive anticlockwise zonal rotation relative to the SPC
of + 1° every 53days, as well as some wandering of individual cyclones.
There are large variations in the spacing of the cyclones around the pen-
tagon, associated with the opening and closing of a gap that is always
present between two of the cyclones. Just as in the north, the cyclones
have preserved their individual morphologies over the seven months
of observations.
Two questions arise from these data. The first is why the penta-
gon and octagon drift so slowly or not at all. By Stokes’ theorem, net
cyclonic vorticity at the centre would imply cyclonic circulation around
the periphery. The other question is why the vortices do not merge.
Saturn has a single cyclonic vortex at each pole. By analysing the con-
ditions for formation of each Saturn vortex and comparing them with
the conditions on Jupiter, it was predicted that the polar circulation
could be different on Jupiter
9
. Some studies
21
, applying the theory to
the merger of Jupiter’s white ovals in 1998–2000, have also shown that
like-signed vortices merge on a fast, advective timescale of four months
when they are no longer separated by opposite-signed vortices in a
single path, a ‘vortex street’. Mergers of the polar cyclones are possible,
but they have not occurred over seven months of observation, nor
is there any evidence of new structures appearing inside the cyclone
polygons. Finally, on the other hand, other studies22,23 show that poly-
gonal vortex patterns (vortex crystals) can develop owing to interaction
with a background of weaker vorticity and last indefinitely in a two-
dimensional Euler flow.
Online Content Methods, along with any additional Extended Data display items and
Source Data, are available in the online version of the paper; references unique to
these sections appear only in the online paper.
Received 24 July; accepted 15 November 2017.
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Acknowledgements The JIRAM project is founded by the Italian Space Agency
(ASI). In particular this work has been developed under the ASI-INAF agreement
number 2016-23-H.0. The JunoCam instrument and its operations are funded
by the National Aeronautics and Space Administration. A portion of this
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was supported by NASA funds to the Juno project and by NSF grant number
1411952.
Author Contributions A.A. and C.H. are the Juno mission instrument leads
for the JIRAM and JunoCam instruments, respectively, and they planned and
implemented the observations discussed in this paper. S.J.B. and J.E.P.C. are
respectively the principal and the deputy responsible for the Juno mission. A.A.,
A. Mura, G.O., J.R., A.I. and F.T.-V. were responsible for writing substantial parts
of the paper. M.E.O’N. helped with the interpretation of the cyclonic structure.
A. Mura, F.A., M.L.M. and D.G. were responsible for reduction and measurement
of the JIRAM data and their rendering into graphical formats. G.E., T.M., G.O. and
J.R. were responsible for the same tasks for JunoCam data. F.T.-V. and F.F. were
responsible for the geometric calibration of the JIRAM data. G.F., G.S., B.M.D. and
S.S. were responsible for the JIRAM data radiance calibrations. A.C., R.N. and
R.S. were responsible for the JIRAM ground segment. S.K.A., J.I.L., A. Migliorini,
D.T, G.P. and D.T. supervised the work. C.P., A.O. and M.A. were responsible for
the JIRAM project from the Italian Space Agency side.
Author Information Reprints and permissions information is available at
www.nature.com/reprints. The authors declare no competing financial
interests. Readers are welcome to comment on the online version of the paper.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional
claims in published maps and institutional affiliations. Correspondence and
requests for materials should be addressed to A.A. (alberto.adriani@iaps.inaf.it).
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Juno mission's rst perijove passage. Geophys. Res. Lett. 44, 4607–4614
(2017).
16. Adriani, A. et al. JIRAM, the Jovian Infrared Auroral Mapper. Space Sci. Rev. 213,
393–446 (2017).
17. Adriani, A. et al. Juno’s Earth yby: the Jovian Infrared Auroral Mapper
preliminary results. Astrophys. Space Sci. 361, 272 (2016).
18. Hansen, C. J. et al. JunoCam: Juno’s Outreach Camera. Space Sci. Rev. 213,
475–506 (2017).
19. Theiss, J. A generalized Rhines eect and storms on Jupiter. Geophys. Res. Lett.
33, L08809 (2006).
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to vortex crystals. Phys. Res. Lett. 75, 3277–3280 (1995).
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Letter
reSeArCH
METHODS
The Jovian InfraRed Auroral Mapper. The Jovian InfraRed Auroral Mapper
(JIRAM) is composed of an imager and a spectrometer that share the same
telescope16,17. The imager focal plane is equipped to observe the planet through
a bandpass filter centred at 4.78 μ m with a 480-nm bandwidth (M-band) and
a bandpass filter centred at 3.45 μ m with a 290-nm bandwidth (L-band). The
spectrometer’s slit is optically co-located with the imager’s field of view and its
spectral range covers the 2–5-μ m interval in 336 spectral bins (bands) resulting in
a spectral sampling of 8.9 nm per band across the full spectral range. The instru-
ment design allows for acquisition of simultaneous imager and spectrometer
observations: in this study, we used the data from the M-band filter, which covers
a field of view of about 1.75° by 6° with 128 × 432 pixels. The instantaneous field
of view is 240μ rad (see ref. 16 for instrumental details).
At the time of the observations, the Juno spacecraft was spinning almost per-
pendicular to the orbital plane. For each spin, JIRAM takes two images: one to the
target (nadir direction), and one to the anti-nadir direction, to evaluate the back-
ground, which is removed onboard. JIRAM is also equipped with a de- spinning
mirror that compensates for the spacecraft rotation and enables it to keep the target
image in the field of view during the data acquisition. The de-spinning mirror may
also be activated at different times with respect to the nadir direction, allowing
a scan of the planet in the spacecraft’s spinning plane. No pointing outside the
spinning plane is permitted.
The data shown in this paper (integrated radiance from 4.5 μ m to 5 μ m) have
been taken with 12 ms of integration time, resulting in a noise-equivalent radiance
lower than 5 × 105Wsr1m2. Table 1 shows exact times of observations (start
time, stop time and number of observations in that sequence or scan). JIRAM
observed both poles with high image quality and spatial resolution during PJ4 and
PJ5. Polar coverage during PJ4 was complete for regions within 30° latitude of both
poles with a spatial resolution varying between 12 km per pixel and 96 km per pixel
for the north pole and between 21 km per pixel and 62 km per pixel for the south
pole. JIRAM coverage of the poles during PJ5 was incomplete, limited by JIRAM’s
field of view and Junos spin axis orientation at perijove.
For PJ4 at the north pole we have complete data coverage with good emission
angle (that is, close to 90°), but to cover other parts of the planet we also use
radiance emitted at lower angles. Such radiance is partially depleted because the
absorption due to cold clouds occurs over a longer atmospheric path. A simple
correction was applied, mainly with the purpose of better identifying the same
features at both PJ4 and PJ5. Since during PJ4 JIRAM observed the same regions
of the north pole at different emission angles, those data were used to compile a
look-up table that, given radiances measured at emission angles lower than 90°,
permits scaling of the measured values to the radiances expected at 90° to make
the measurements more comparable to each other.
Data are jovian-located and then re-projected in System III planetocentric
geographical coordinates, using a polar orthographic projection. Geometric infor-
mation was obtained by using ad hoc algorithms based on the NAIF-SPICE tool
24
for each image. JIRAM raw data are calibrated in units of radiance (Wm
2
sr
1
)
as described16,17. The responsivity used in this study has been revised to a flat value
of 2 × 106 digital numbers (DN) per (Wm2sr1) by using the cruise-calibration
campaign data, performed by using the orange giant star Aldebaran (α Tauri) as
a reference target.
Finally, the diameters of the cyclones are calculated on the JIRAM infrared
images, defining the outer border of the cyclone where the smaller, anticyclonic
structures form and planetocentric coordinates are used throughout this report.
Images from JIRAM were processed using Matlab (Fig. 1 and Extended Data Fig. 1)
and ENVI-IDL (Fig. 3).
Processing of consecutive images allows for animations revealing motion, as
well as for quantitative analysis of cloud velocities. JIRAM data in Extended Data
Table 1 have been arranged in animations that show the movement of single
vortices during PJ4 observations. Each sequence or scan has been composed into
a mosaic, and then each mosaic became a frame of the video. We provide nine
Supplementary Videos for the north pole (eight for circumpolar cyclones plus
the NPC); each video is made of 11 images. We also provide six Supplementary
Videos for the south pole (five for circumpolar cyclones plus the SPC); each video
is made of 6 images.
JunoCam. JunoCam is a visible-spectrum camera designed to acquire images
through broadband red, green and blue filters mounted directly on a CCD
detector, with an 889-nm methane absorption band filter acquiring an image on a
separate rotation typically 30 s later. JunoCam is rigidly mounted on the spinning
spacecraft. That way, it uses the spacecraft rotation to take a full panorama within
about 30 s consisting of up to 82 narrow exposures, referred to as the ‘pushframe
mode. Usually, it takes partia l panoramas of the target of interest. The camera has
a horizontal field of view of about 58°, and a Kodak KAI-2020 charge-coupled
device (CCD) sensor with four filter stripes, a red, a green, a blue (RGB) and a
narrow-band 890-nm infrared filter attached on the 1,600 × 1,200 light-sensitive
pixels. For each of the four filters, there is an corresponding readout region of
1,600 × 128 pixels which can be transferred into the resulting raw image. This
transfer is not immediate, but the 12-bit data number of each pixel is encoded as
an 8-bit value, and tiles of 16 × 16 pixels are compressed in either a lossy or lossless
manner. Usually, the encoding of the 12-bit data as an 8-bit value is nonlinear,
according to a ‘companding’ function. Motion blur is mostly avoided by a technique
called time delay integration. In colour (RGB) mode, for each exposure, three of
the four readout regions are added as stripes to the raw image. Full details of the
instrument and its operation are available in ref. 18.
JunoCam observed the same polar regions as JIRAM on PJ4 and PJ5—as well
as complementary longitudinal regions on PJ1 and PJ3—but as a visible imager, it
acquires images in reflected light. A complete polar view must be pieced together
from the unshadowed portions of images collected during multiple perijove passes.
Observations were made in both north and south polar regions during PJ1, PJ3,
PJ4 and PJ5. Polar imaging in PJ5 was scheduled over extended periods of time
to cover more longitudes as the planet rotates through daylight, which enabled
time-lapse measurments that include measurements of rotation of the cyclones.
With an approximate geometrical camera model, including its pointing for each
exposure, the appropriate three-dimensional vector was calculated for each pixel in
a given reference frame, for example, J2000. Position and pointing information are
inferred from SPICE data
24
, with some manual adjustment. Jupiter is modelled as
a MacLaurin spheroid on Jupiter’s 1-bar level. A planetocentric coordinate system
assigns a three-dimensional position to each longitude/latitude pair. The three-
dimensional vector, pointing from Juno to the three-dimensional position, com-
pletes the connection of each longitude/latitude pair to colour information. With
this method, each raw JunoCam image of Jupiter is reduced to an approximately
geometrically calibrated polar-map projection.
Because Jupiter is rotating and Juno is moving rapidly, the illumination for each
JunoCam image changes rapidly. Comparison of images requires approximate normali-
zation of the images. For now, this is achieved in a heuristic way, essentially stretching
contrast over regions of approximately similar solar incidence angles, subtracting
the mean brightness for these bins, and accounting for changing light scattering
of a presumed haze layer as a function of emission angle, which can be obtained for
sufficiently small crops by high-pass filtering. For the JunoCam maps shown in Figs 1
and 2, this correction was made down to a maximum solar illumination angle of
66°, above which the signal-to-noise ratio drops below a value of 3 per pixel. Further
nonlinear brightness stretching and saturation enhancement brings out detail.
Time sequences of 2 to 3 frames of polar images were made on all perijove passes
to track cloud motions. After PJ1, it was clear that the limited time sequence on that
orbit verified the visible impression that the features surrounding the poles whose
‘arms’ implied cyclonic motion really were cyclones. A special effort was made in PJ5
to create longer sequences of time-lapse images that would illustrate subtler motions
of the polar features by imaging over a longer time interval. The sequences given
below represent three of the best of those animations. A sequence of images from
the north pole is available at http://junocam.pictures/gerald/uploads/20170424/
anim/jnc_pj05_N_089_to_105_blend4_enh.html. A sequence of images from the
south pole is available at http://junocam.pictures/gerald/uploads/20170331/anim/
jnc_pj05_polarS_60px_lin_interpolated_21frames_1200x1200.html. A close-up
version of that south polar sequence is available at http://junocam.pictures/
gerald/uploads/20170406/anim/jnc_pj05_south_polar_animation_111_to_121_
8frames_20fps_1200px.html.
History and terminology of cyclone clusters. The term ‘ditetragonal’ has
been introduced in the context of crystallography, since it is one of the ten two-
dimensional crystallographic point groups (see table 10.1.2.1 in ref. 25). In the
non-Euclidean geometry of the curved polar region, a two-dimensional pentag-
onal rather than a hexagonal pattern would be conceivable, similar to the surface
of a pentagon-dodecahedron (see table 10.1.2.2 in ref. 25). But since the size of
the vortices does not fit exactly to the geometry of a pentagon-dodecahedron, an
unstable structure switching between a hexagon and pentagon could occur, or an
oscillating pentagon for vortices of similar sizes. Besides the ‘vortex crystals’
22,23
mentioned above, similar vortex patterns also occur in rotating superfluid helium II
for quantum-mechanical reasons26. Theoretical predictions of such quantized
vortices reach back to Onsager
27
and Feynman
28
, although Landau
29
introduced
rotons in 1941. The first experimental observations30 were in 1979.
Data availability. The data used for this study will be available once the proprietary
period ends, namely about six months after the data were collected by Juno, from
the NASA’s Planetary Data System at https://pds.jpl.nasa.gov/tools/data-search/.
The JunoCam data are all available for direct download from the Mission Juno web
site in both raw and processed form: https://www.missionjuno.swri.edu/junocam/
processing.
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Content courtesy of Springer Nature, terms of use apply. Rights reserved
Letter reSeArCH
24. Acton, C. H. Ancillary data services of NASA’s navigation and ancillary
information facility. Planet. Space Sci. 44, 65–70 (1996).
25. Hahn, Th. (ed.) International Tables for Crystallography Vol. A, 5th edn, 768, 786
(Springer, 2005).
26. Aref, H. et al. Vortex crystals. Adv. Appl. Mech. 39, 1–79 (2003).
27. Gorter, C. J. The two uid model of helium II. Nuovo Cimento 6 (Suppl. 2),
245–250 (1949); see discussion by L. Onsager, 249–250.
28. Feynman, R. P. in Progress in Low Temperature Physics Vol. 1 (ed. Gorter, C. J.)
Ch. II, 17–53 (Elsevier, 1955).
29. Landau, L. D. The theory of superuidity of helium II. Zh. Eksp. Teor. Fiz. 11, 592
(1941).
30. Yarmchuk, E. J., Gordon, M. J. V. & Packard, R. E. Observation of stationary
vortex arrays in rotating superuid helium. Phys. Rev. Lett. 43, 214–217
(1979).
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Content courtesy of Springer Nature, terms of use apply. Rights reserved
Letter
reSeArCH
Extended Data Figure 1 | Comparison of the polar cyclonic structures
between PJ4 and PJ5. Here is the comparison between JIRAM 5-μ m
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.
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Letter reSeArCH
Extended Data Figure 2 | 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.
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Letter
reSeArCH
Extended Data Table 1 | JIRAM start time, stop time and number of observations for the different datasets used for this study
utc
, coordinated universal time. (1) Approach phase, low resolution; used only to ll small gaps in Fig. 1; (2) minimum emission angle, high resolution, used to make most of the mosaic in Fig. 1.
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Letter reSeArCH
Extended Data Table 2 | Details of the JunoCam observations
The observations listed correspond to those used in Figs 1 and 2 and in Extended Data Fig. 2.
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2.
3.
4.
5.
6.
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  • ... On February 2 nd 2017, during the fourth fly-by, JIRAM had the opportunity to observe the polar atmosphere of Jupiter for the first time [Adriani et al. 2018]. Those observations, together with those of the visible JunoCam imager [Hansen et al, 2014], allowed us to survey for the first time the dynamical structure of the polar atmosphere of the planet. ...
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    ... In Figures 2 and 3 we present the sequence of ten South Pole observations summarized in Table 1. As already stated by Adriani et al. [2018] following the PJ4 observation in February 2017, the South Pole configuration is quite different from the northern one. The South Pole observations have continued on regular basis, and here we report about the evolution between PJ4 and PJ18. ...
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  • ... Most recently, the Juno mission has significantly extended the observational record to include close orbital passes over both poles of Jupiter, where a whole new set of phenomena have been discovered. At high latitudes, Jupiter's cloud bands and zonal jets are much less evident and the dominant features close to the poles are regular arrays of almost circular, cyclonic vortices surrounding a single cyclone sitting close to the pole itself (Adriani et al. 2018). Infrared images (Adriani et al. 2018) reveal a wealth of small-scale structure associated with such vortices, but most remarkable is the extent to which the eightfold or fivefold cyclone arrays have remained stable and persistent over timescales of at least 1-2 years. ...
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  • ... The Juno mission's JunoCam instrument , conceived as a publicoutreach camera, has provided a surprising wealth of scientific results. These include the first close-up examination of Jupiter's polar regions (Orton et al. 2017a), in particular the unexpected presence and properties of constellations of cyclonic vortices around each pole (Adriani et al. 2018a, Tabataba-Vakili et al. 2020). JunoCam's proximity to Jupiter's cloud tops has also provided high-resolution details of Jupiter's Great Red Spot and its environment ). ...
    ... Current SPICE data show good agreement with these maps, with the limb-fitting approach showing an uncertainty better than 2° in the position of the south pole, as reported by Tabataba-Vakili et al. (2020). Further details of this mapping process are provided by Adriani et al. (2018a: see their Supplementary Information) and by Tabataba-Vakili et al. (2019). All JunoCam images are publicly available on the Mission Juno web site: https://www.missionjuno.swri.edu/junocam/processing. Figure 1 shows an example of a full JunoCam image, rendered in a cylindrically mapped format, together with an excerpt ("crop") of the image in which we identify wave-like features. ...
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  • ... The inhomogeneous pattern of 5 μm emission is primarily observed from ground-based facilities (Westphal 1969;Harrington et al. 1996;Ortiz et al. 1998), since the terrestrial atmosphere has good transparency in the infrared M-band (Tokunaga 2000), and large telescopes can provide images with excellent angular resolution, particularly when improved with an adaptive optics approach or a lucky-imaging approach , where many short exposures are taken and the sharpest frames are co-added. NASA's giant planet flagship orbiters, Galileo and Cassini, carried imaging spectrometers that covered the 5 μm range (Carlson et al. 1992;Miller et al. 1996), and Juno's JIRAM instrument has produced low-resolution spectra and stunning images of Jupiter's atmosphere, particularly in polar regions (Sindoni et al. 2017; Adriani et al. 2018b). ...
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  • Preprint
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    The Cassini and Juno probes have revealed large coherent cyclonic vortices in the polar regions of Saturn and Jupiter, a dramatic contrast from the east-west banded jet structure seen at lower latitudes. Debate has centered on whether the jets are shallow, or extend to greater depths in the planetary envelope. Recent experiments and observations have demonstrated the relevance of deep convection models to a successful explanation of jet structure and cyclonic coherent vortices away from the polar regions have been simulated recently including an additional stratified shallow layer. Here we present new convective models able to produce long-lived polar vortices. Using simulation parameters relevant for giant planet atmospheres we find flow regimes that are in agreement with geostrophic turbulence (GT) theory in rotating convection for the formation of large scale coherent structures via an upscale energy transfer fully three-dimensional. Our simulations generate polar characteristics qualitatively similar to those seen by Juno and Cassini: they match the structure of cyclonic vortices seen on Jupiter; or can account for the existence of a strong polar vortex extending downwards to lower latitudes with a marked spiral morphology and the hexagonal pattern seen on Saturn. Our findings indicate that these vortices can be generated deep in the planetary interior. A transition differentiating these two polar flows regimes is described, interpreted in terms of different force balances and compared with previous shallow atmospheric models which characterised polar vortex dynamics in giant planets. In addition, the heat transport properties are investigated confirming recent scaling laws obtained in the context of reduced models of GT.
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    We present a power spectral analysis of two narrow annular regions near Jupiter’s South Pole derived from data acquired by the Jovian Infrared Auroral Mapper (JIRAM) instrument onboard NASA’s Juno mission. In particular, our analysis focuses on the dataset acquired by the JIRAM M‐band imager (hereafter IMG‐M) that probes Jupiter’s thermal emission in a spectral window centered at 4.8 μm. We analyze the power spectral densities of circular paths outside and inside of cyclones on images acquired during six Juno perijoves (PJ). The typical spatial resolution is around 55 km pixel⁻¹. We limited our analysis to six acquisitions of the South Pole from February 2017 to May 2018. The power spectral densities both outside and inside the circumpolar ring seem to follow two different power laws. The wavenumbers follow average power laws of ‐0.9±0.2 (inside) and ‐1.2±0.2 (outside), and of ‐3.2±0.3 (inside) and ‐3.4±0.2 (outside), respectively beneath and above the transition in slope located at ~ 2.×10⁻³ km⁻¹ wavenumber. This kind of spectral behavior is typical of two‐dimensional turbulence. We interpret the 500 km length scale, corresponding to the transition in slope, as the Rossby deformation radius. It is compatible with the dimensions of a subset of eddy features visible in the regions analyzed, suggesting that a baroclinic instability may exist. If so, it means that the quasi‐geostrophic approximation is valid in this context.
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    We describe a simple classroom demonstration of a fluid-dynamic instability. The demonstration requires only a bucket of water, a piece of string and some used tealeaves or coffee grounds. We argue that the mechanism for the instability, at least in its later stages, is two-dimensional barotropic (shear-flow) instability and we present evidence in support of this. We show results of an equivalent basic two-dimensional numerical non-linear model, which simulates behavior comparable to that observed in the bucket demonstration. Modified simulations show that the instability does not depend on the curvature of the domain, but rather on the velocity profile.
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    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.
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    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.
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    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.
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    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.
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    The Juno spacecraft acquired direct observations of the jovian magnetosphere and auroral emissions from a vantage point above the poles. Juno’s capture orbit spanned the jovian magnetosphere from bow shock to the planet, providing magnetic field, charged particle, and wave phenomena context for Juno’s passage over the poles and traverse of Jupiter’s hazardous inner radiation belts. Juno’s energetic particle and plasma detectors measured electrons precipitating in the polar regions, exciting intense aurorae, observed simultaneously by the ultraviolet and infrared imaging spectrographs. Juno transited beneath the most intense parts of the radiation belts, passed about 4000 kilometers above the cloud tops at closest approach, well inside the jovian rings, and recorded the electrical signatures of high-velocity impacts with small particles as it traversed the equator.
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    On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter, passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter’s poles show a chaotic scene, unlike Saturn’s poles. Microwave sounding reveals weather features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow low-latitude plume resembling a deeper, wider version of Earth’s Hadley cell. Near-infrared mapping reveals the relative humidity within prominent downwelling regions. Juno’s measured gravity field differs substantially from the last available estimate and is one order of magnitude more precise. This has implications for the distribution of heavy elements in the interior, including the existence and mass of Jupiter’s core. The observed magnetic field exhibits smaller spatial variations than expected, indicative of a rich harmonic content.
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    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.
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    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.
  • Article
    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.
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    Full-text available
    JIRAM is an imager/spectrometer on board the Juno spacecraft bound for a polar orbit around Jupiter. JIRAM is composed of IR imager and spectrometer channels. Its scientific goals are to explore the Jovian aurorae and the planet's atmospheric structure, dynamics and composition. This paper explains the characteristics and functionalities of the instrument and reports on the results of ground calibrations. It discusses the main subsystems to the extent needed to understand how the instrument is sequenced and used, the purpose of the calibrations necessary to determine instrument performance, the process for generating the commanding sequences, the main elements of the observational strategy, and the format of the scientific data that JIRAM will produce. Keywords Juno · Jupiter · Image spectrometer · Jovian atmosphere · Jovian aurorae