Europlanet Science Congress 2021
Virtual meeting
13 – 24 September 2021
Europlanet Science Congress 2021
Virtual meeting
13 September – 24 September 2021

OPS4

A new view of Jupiter, Saturn, and giant planets from the polar-orbiting Juno and Cassini spacecraft

The Juno mission is providing crucial new data sets addressing Jupiter's interior, atmosphere and magnetosphere that challenge current theories of formation, evolution and dynamics of both Jupiter and giant planets in general. The Juno results when combined with data sets from previous missions such as Cassini, Galileo, and Voyager as well as exoplanet observations and models, is providing a new opportunity for the study of comparative planetology. This session welcomes contributions on a wide variety of topics regarding Jupiter, Saturn and giant planets in general: gravity and magnetic field analysis and interpretation, giant planet magnetospheres, aurorae, radiation environments, atmospheric dynamics, planet interiors and satellite interactions. The session also welcomes remote observations acquired in support of Juno and Cassini, and discussions of formation scenarios and evolutionary pathways of planetary bodies in our Solar System and beyond.

Convener: Yasmina M Martos | Co-conveners: Arrate Antunano, Scott Bolton, Bertrand Bonfond, George Clark, Stavros Kotsiaros, Yamila Miguel

Session assets

Discussion on Slack

Oral and Poster presentations and abstracts

Chairpersons: Arrate Antunano, Yamila Miguel, Yasmina M Martos
Atmosphere: composition, dynamics
EPSC2021-173
|
solicited
Henrik Melin, Leigh Fletcher, Patrick Irwin, and Davide Grassi

The polar orbit of the Juno spacecraft provides an unprecedented view of Jupiter's atmosphere as it passes above the cloud tops every 53 days. The spectrum in the near infrared is dominated by reflected sunlight from aerosols (both condensate clouds and hazes) in the troposphere, as well as absorptions by the molecular species present. In addition, thermal emission longward of 4.5 µm provides access to the gaseous composition and aerosols below the top-most clouds.  Of particular importance in shaping the spectra are ammonia, phosphine and water, in addition to minor contributions from species such as arsine, germane and carbon monoxide. These regions also include emissions by ionospheric H3+. Here, we produce meridionally averaged zonal profiles from the Juno-JIRAM observations obtained during PJ3, which provide almost complete latitude coverage. To analyse the observations, we use the radiative transfer and retrieval code NEMESIS (Irwin et al., 2008), which has been updated to cover this wavelength with the latest line-data from HITRAN. Our aim is to analyse both the reflected-sunlight region (2-4 µm) and the thermal emission region (4-5 µm) simultaneously for the first time, building on the work of Grassi et al. (2019) and Grassi et al. (2020).  We investigate the appropriate set of aerosol and haze layers, starting with NH4SH at 1.3 bars, NH3 and 0.7 bars and two grey hazes: one in the troposphere and one in the stratosphere.  The optical properties of these aerosols are tested to find the optimal cloud structure to reproduce the full JIRAM spectrum. From the retrievals of the zonally-averaged spectra we investigate whether spatial variations of tropospheric composition are truly required to fit the data, comparing gaseous contrasts to the expected circulation patterns associated with Jupiter’s belts and zones.

How to cite: Melin, H., Fletcher, L., Irwin, P., and Grassi, D.: Zonal Profiles of Jupiter's Tropospheric Abundances from Near-Infrared Juno JIRAM Spectroscopy, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-173, https://doi.org/10.5194/epsc2021-173, 2021.

EPSC2021-59
Glenn Orton, James Sinclair, Angela Burke, Takuya Fujiyoshi, Yasumasa Kasaba, Thomas Momary, Ryan Chan, and Leigh Fletcher

Motivation

Recent close-up views of Jupiter’s polar regions by NASA’s Juno spacecraft are providing a wealth of information about the dynamics and composition of Jupiter’s poles. We present thermal imaging observations from a series of repeated observations over fifteen years.  These images complement the observations made by the Juno spacecraft by observing in a spectral region not covered by its instrumentation, providing a near-global context for the narrow fields-of-view of Juno’s Microwave Radiometer and JunoCam instruments and providing a long term baseline to study Jovian atmospheric evolution. In this work, we specifically focus on the distinct thermal signatures of Jupiter’s northern and southern polar regions in both the troposphere and stratosphere. Although Cassini CIRS maps of Jupiter in 2000 could see this transition to coll polar vortices (e.g. Simon-Miler et al. 2006, Fletcher et al. 2016), the spatial resolution of the 8-m facility provides access to higher latitudes.

Data

We present thermal imaging from the Subaru Telescope using the COoled Mid-Infrared Camera and Spectrometer (COMICS, Kataza et al., 2000), between 7.8 and 25 μm. These data map temperatures in the upper troposphere (100 – 500 mbar) and stratosphere (20 – 0.5 mbar), and they constrain the distribution of tropospheric gases and condensate aerosols. This data set covers 2005 to 2020, allowing for the investigation of long-term trends, as well as comparisons with Juno and Juno-supporting observations at other wavelengths from 2016 onward.   

Preliminary Results

Figure 1 illustrates the composite polar maps of brightness temperature for each hemisphere using images measured in January, 2017. The retrieved temperatures in each latitude circle were derived from these data were binned over  μ (= cosine of emission angle) and the centre-to-limb variation was inverted using the NEMESIS radiative transfer code (Irwin et al., 2008). The results demonstrated that tropospheric temperatures exhibit a steep decline of at least 2 K poleward of 60°N-63°N (planetocentric), which we believe marks the boundary of a tropospheric polar vortex. A similar drop in temperature takes place more gradually over 54°S-64°S. The precise latitude of the inferred vortex boundary varies slightly between observations in both hemispheres. No seasonal trends in these latitude variations were observed. Stratospheric polar temperatures are affected by auroral-related heating at 140° – 230°W (System III) at high-northern latitudes (>55°N) and 330° – 90°W at high-southern latitudes (<70°S).  Away from regions affected by auroral heating, the boundaries of the vortex in the stratosphere appear to be similar to those in the troposphere, as stated above.  However, unlike the uniformly colder temperatures of the polar vortices in the troposphere, temperatures in the polar vortices in the stratosphere appear be the same or even warmer than lower latitudes, with the south polar region appearing warmer and the north polar region cooler in 2016-2020.  To first order, the zonally variable latitude boundaries of the polar vortices appear to be coincident with the boundaries of distinct regions of overlying hazes known as the polar caps, which are detected in reflected sunlight.  This suggests the dynamical boundaries are controlled by a Rossby wave and important contributions by these aerosols to the radiative balance within these polar regions (see Zhang et al 2015, Guerlet et al. 2020).

Figure 1. Polar projection of brightness temperatures in Jupiter from observations made by the Subaru/ COMICS instrument in January of 2017.  The top panels for the north (left) and the south (right) display a composite brightness temperature map for observations made with a filter centered at 7.80 µm that is sensitive to stratospheric temperatures near 10 mbar of atmospheric pressure. The bottom panels for the north (left) and south (right) are made similar with a filter centered at 17.65 µm that is sensitive to temperatures near 190 mbar of atmospheric pressure.

The location of polar-vortex temperature change is indicated by the arrows.  The cooler temperatures associated with the north polar vortex at 190 mbar (upper left) is the most prominent. There is essentially no meridional stratospheric temperature change detectable at high-southern latitudes (lower right); the compact brightening close to 0° W longitude is the result of auroral-related heating of the stratosphere (see, for example, Sinclair et al., 2021, and references therein).

References

Fletcher, L. N. et al. 2016.  Icarus. 278, 128-161.

Guerlet, S., et al. 2020. Icarus, 351:113935. doi: https://doi.org/10.1016/j.icarus.2020.113935. 129

Irwin, P. G. J. et al. 2008. J. Quant. Spectr. Rad. Transfer 109, 1136-1150. 

Kataza, H. et al. 2000. Proc. SPIE 4008, 114-1152

Simon-Miller, et al. 2006. Icarus 180, 98-112.

Sinclair, J. A. et al. 2019. Nature Astronomy 3, 607-613.

Zhang, X., R. A. 2016. Nature Communications 6:10231. Doi 10.1038/ncomms10231.

How to cite: Orton, G., Sinclair, J., Burke, A., Fujiyoshi, T., Kasaba, Y., Momary, T., Chan, R., and Fletcher, L.: Jupiter’s  Polar Vortices in the Mid-Infrared as Observed by Subaru/COMICS Prior to and During the Juno Mission, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-59, https://doi.org/10.5194/epsc2021-59, 2021.

EPSC2021-190
|
ECP
Padraig Donnelly, Aymeric Spiga, Sandrine Guerlet, and Matt James

Abstract

The Saturn DYNAMICO Global Climate Model (GCM) is a high-resolution, multi-annual numerical simulation of Saturn’s atmospheric dynamics [1], combining a radiative-convective equilibrium model [2] and a hydrodynamical solver on an icosahedral grid. The model reproduces well the observed behaviour of jets and eddy-momentum transfer to the mean flow. Vortices arise naturally in the model over time but until now they have not been given direct consideration.

Analysis of large-scale vortices in the GCM is performed by investigating; (1) the long-term statistical distribution and organization of vortices and (2) the short-term evolution of individual discrete features. The metrics used in both studies provide direct comparison to observations, albeit with some methodological differences.

Long-term analysis

This study uses a vortex selection method similar to previous observational studies of Jupiter and Saturn [3, 4, 5, 6]. We seek to address whether the Saturn GCM replicates the hemispheric symmetries and asymmetries of vortices measured on Saturn by [4, 5, 6], as well as studying the formation conditions and long-term temporal evolution of vortex distributions.

Those studies collectively observe Saturn intermittently over roughly one half of a Saturnian year between northern winter and summer solstice. The Saturn GCM offers a much-expanded view with a timeseries spanning three full model years after spin-up (to be extended further by four years), with vortex measurements obtained at each seasonal peak.

The model offers consistent spatial resolution across each global map throughout the timeseries (½-degree latitude-longitude bins corresponding to ~10-500 km/pixel from pole-equator). It constrains well the size and location of vortices, the horizontal wind field components and the magnitude and sign of horizontal vorticity.

Figure 1: Overall distribution of high-latitude vortices at ~700 mbar level for entire timeseries. (Left) histogram of vortex count with mean atmospheric temperature in red. (Centre) instantaneous zonal wind speed at the vortex centre with the mean zonal wind profile. (Right) average vortex size (average of major and minor axes) and vorticity sign with Rossby deformation radius (LD, orange) and the Rayleigh Kuo-criterion for barotropic instability (R-K, black). Mean profiles are averaged over the entire timeseries and shaded areas represent one standard deviation between all individual profiles.

Short-term analysis

This method is also applied to short term model outputs to investigate the appearance and disappearance, lifetime vs. size relationship, latitudinal and longitudinal drift and merging events. This analysis allows for the tracking of “ambiguous blobs” of vorticity with a cadence of 1 model day to study the thermal and dynamical conditions related to cyclogenesis and vortex evolution. This also provides insights into vortex behaviour and the proximity interactions with the local flow, jets, and other vortices.

Summary and Conclusions

The long-term analysis reveals that the Saturn GCM can largely replicate well the trends seen in previous observations. Some disagreement with the data can be explained methodologically. Otherwise, this presents avenues of future study like refinement of the method (employing a machine learning approach for vortex detection), inclusion of more detail in model (e.g., moist convection) and exploration of the primordial epoch of the model (for a deeper understanding of vortex behaviour in the absence of strong zonal circulations).

PTD and the France authors were supported by Agence Nationale de la Recherche (ANR) and the UK author acknowledges the Science and Technology Facilities Council (STFC).

References

[1] Spiga et al. (2020), Icarus, 335, http://dx.doi.org/10.1016/j.icarus.2019.07.011.

[2] Guerlet et al. (2014), Icarus, 238, https://doi.org/10.1016/j.icarus.2014.05.010.

[3] Li et al. (2004), Icarus, 172, https://doi.org/10.1016/j.icarus.2003.10.015.

[4] Vasavada et al. (2006), J. Geophys. Res. Planets, 111, https://doi.org/10.1029/2005JE002563.

[5] Trammell et al. (2014), Icarus, 242, https://doi.org/10.1016/j.icarus.2014.07.019.

[6] Trammell et al. (2016), J. Geophys. Res. Planets, 121, https://doi.org/10.1002/2016JE005122.

 

How to cite: Donnelly, P., Spiga, A., Guerlet, S., and James, M.: Statistical Analysis of Large-Scale Vortices in the Saturn DYNAMICO GCM, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-190, https://doi.org/10.5194/epsc2021-190, 2021.

EPSC2021-57
John Rogers, Gerald Eichstädt, Candice Hansen, Glenn Orton, and Thomas Momary

Introduction

The polygons of cyclones at Jupiter’s poles – a pentagon at the south pole and an octagon at the north pole, each centred on another cyclone – were discovered at Juno’s first few perijoves by the JunoCam and JIRAM instruments [ref.1].  JunoCam images showed that the configurations remained stable for the next two years, up to perijove (PJ) 15 [ref.2].  Here we summarise their behaviour up to PJ33 in 2021 April; with the orbital period of 53 days, this covers 4½ years.

The data are polar projection maps produced from JunoCam images as described in [ref.2].

South polar cluster

The five southern circumpolar cyclones (CPCs) surround the central South Polar Cyclone (SPC).  However, the SPC is not at the pole, but displaced by 1°-3° latitude, always into the same quadrant of longitude; and there is a gap between two of the CPCs (CPC-1 & 2), in the same quadrant [ref.2].

This asymmetry of the pentagon has persisted until now (Figures 1&2).  At PJ23 a smaller, compact cyclone was present in the gap, suggesting that the pentagon might be turning into a hexagon, but at PJ24 it was replaced by a chaotic cyclonic region and the asymmetric pentagonal structure was then restored.

We proposed [ref.2] that the cluster is a ‘vortex crystal’ whose configuration could be explained geometrically, if we adopt two conjectures: that the cyclones have a maximum size that prevents them growing larger or merging, and that the central cyclone must be smaller than the mean size of the others (as observed).  In this case, tight packing of the cyclones  produces a pentagon with a gap; and to pack the cyclones as close as possible to the pole, the cluster must be displaced towards the side of the gap, with the largest cyclone on the opposite side, as observed. 

Consistent with this model, as the cluster wanders somewhat, the gap tends to be widest when the SPC is furthest from the pole (Figure 3).  However, when the SPC longitude is greatest, it lies alongside CPCs-2 & 3 rather than CPCs-1 & 2; and at these times a gap opens up between CPCs-2 & 3, supplementing or replacing the gap between CPCs-1 & 2, as the model would predict.  

We noted [ref.2] that the wandering of the SPC appeared to be cyclic.  The record over 4½ years confirms this, showing that it performs loops with a period of 11.5 (±1) months (Figure 4).  The loops are of varying sizes, but show a progressive drift in one direction.  The rate of this drift of cycles has been very uneven, but if it were interpreted as precession of the cycles around the pole, the rate would be ~8° (±8°) per year.

Independently of this cyclic motion, the whole pentagon shows a very slow rotation about the SPC, which is stable in the long term: we estimated +1.5°/PJ from PJ1 to PJ15 [ref.2].  Up to PJ32, the average rotation is  +1.21 (±0.07) °/PJ, i.e. 8.3 (±0.5) °/yr.

Figures 1 & 2.  Maps of the south polar cluster, down to 75°S at the edges.  CPCs are numbered.  The red cross marks the south pole, grey crosses 80°S; L3=0 to left.

Figure 3 (left).  Width of the gap in the pentagon. The angle between CPCs-1 & 2 as measured from the SPC, at each PJ, is plotted against the distance of the SPC from the pole (measurements of the cyclone centres). Brown points represent PJs when there was also a gap between CPCs-2 & 3, i.e. the angle between them was >76° (it is normally ~70°).

Figure 4 (right).  Position of the centre of the SPC (colour-coded by PJ) with respect to the south pole (white cross).  PJs in the first and latest cycles are numbered (except PJ1 & PJ31).  The SPC has been cycling anticlockwise throughout.  Background image from PJ25.

 

North polar cluster

The north polar octagon originally consisted of 8 CPCs of alternating morphology (‘filled’ and more diverse types), so it was best described as a ditetragon, centred on the North Polar Cyclone (NPC) [refs.1 & 2].  JunoCam has less complete coverage of the north polar region than of the south.  Nevertheless, about half the cluster is imaged at each PJ and over four PJs a high-quality map can be assembled (Figure 5).  And as the sun rose on the north pole, the NPC (previously observed only by JIRAM in 5-µm thermal emission) has become visible to JunoCam.

In 2017, the polygon was a ditetragon with one anticyclonic oval (AO) north of CPC-7.  

In 2018, one of the diverse CPCs gradually turned into a fifth ‘filled’ CPC; meanwhile, CPC-7 was increasingly displaced to lower latitude, away from the NPC, by the AO just north of it. By 2020, another AO had appeared on the opposite side, north of CPC-3.

In 2021 (from PJ32 onwards), the AO north of CPC-7 disappeared and CPCs-6 & 8 closed up together. So we discuss whether the cluster is still a (distorted) octagon, or now a heptagon, with CPC-7 excluded from it, joining several smaller ‘filled’-type cyclones as satellites of the polygon (Figure 5).  Moreover, the NPC is displaced by ~0.6-1.2° from the pole – possibly a response to the new asymmetry, comparable to the displacement of the SPC.

These rearrangements could be random, or temporary, or seasonal in response to the sun rising over the north pole.  JunoCam will continue to monitor the polar clusters during the extended mission.

Figure 5:  Composite map of the north polar cluster, PJ30-PJ33, down to 75°N at the edges.  The PJ33 sector was rotated 7° and translated slightly.  CPCs are numbered.  Unnumbered arrows indicate smaller peripheral cyclones (yellow) and anticyclonic ovals (red).

 

Acknowledgements:

Some of this research was funded by NASA. A portion of this was distributed to the Jet Propulsion Laboratory, California Institute of Technology.

References:

1. Adriani et al., Nature 555, 216-219 (2018).

2. Tabataba-Vakili et al., Icarus 335 (2020), paper 113405 (online 2019).

How to cite: Rogers, J., Eichstädt, G., Hansen, C., Orton, G., and Momary, T.: Behaviour of Jupiter’s polar polygons over 4 years, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-57, https://doi.org/10.5194/epsc2021-57, 2021.

EPSC2021-223
|
ECP
Bilal Benmahi, Thibault Cavalié, Thomas K. Greathouse, Vincent Hue, Rohini Giles, Sandrine Guerlet, Aymeric Spiga, and Richard Cosentino

Since 30 years, an equatorial oscillation of the temperature structure with a quasi-period of 4 years has been discovered in the atmosphere of Jupiter (Orton et al. 1991, Leovy et al. 1991). This phenomenon results in a complex vertical and horizontal structure of prograde and retrograde jets. However, the wind structure of the stratosphere in the equatorial zone of Jupiter has not been measured directly. It has only been inferred in the tropical region from the thermal wind balance using temperatures measured in the jovian stratosphere and the cloud-top wind speeds measured as a initial condition (e.g. Flasar et al. 2004). But temperatures are not constrained between the upper troposphere and the middle stratosphere from observations, limiting thus the accuracy of the thermal wind balance.

In this study, we derive self-consistently for the first time the structure of the tropical winds by utilizing wind and temperature observations all performed in the stratosphere. The wind speeds were obtained by Cavalié et al. (2021) at 1 mbar in Jupiter's stratosphere in both the equatorial and tropical regions in March 2017 with ALMA. The stratospheric thermal field was measured a few days before from the equator to the mid-latitudes with Gemini/TEXES (Giles et al. 2020). For the derivation of the wind, we use both the thermal wind equation (Pedlosky 1979) and the equatorial thermal wind equation (Marcus et al. 2019). In this paper, we will present and discuss our results.

How to cite: Benmahi, B., Cavalié, T., Greathouse, T. K., Hue, V., Giles, R., Guerlet, S., Spiga, A., and Cosentino, R.: The equatorial wind structure in Jupiter’s stratosphere from direct wind and temperature measurements with ALMA and IRTF/TEXES, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-223, https://doi.org/10.5194/epsc2021-223, 2021.

EPSC2021-237
Thibault Cavalié, Bilal Benmahi, Thierry Fouchet, Raphael Moreno, Emmanuel Lellouch, Sandrine Guerlet, Aymeric Spiga, and Arielle Moullet

Saturn's cloud-top zonal winds have been measured since the Voyager days. Contrary to Jupiter, the jets are mostly prograde and with a noticeable broad super-rotating jet between 35°S and 35°N with peak velocities reaching ~450 m/s between 10°S and 10°N (e.g. Sanchez-Lavega et al. 2000). The Cassini mission revealed, during its Grand Finale, that these winds extend as deep as 8000 km below the clouds (Galanti et al. 2019). Above the tropopause, in the stratosphere, there has been no direct determination of the zonal winds, although thermal wind balance calculations have shown the signature of Saturn's semi-annual oscillation (SAO) in the tropical zone (Fouchet et al. 2008, Guerlet et al. 2011, 2018). These derivations lack an initial condition, in terms of wind speeds, located in the sensitivity zone of the temperature measurements. It thus remains unknown if the SAO jets alternate in direction as a function of altitude. In addition, more and more sophisticated general circulation models are being developed to constrain the dynamics of Saturn's stratosphere (Friedson & Moses 2012, Spiga et al. 2020, Bardet et al. 2021). These models now crucially need observational constraints.

We used the Atacama Large Millimeter/submillimeter Array (ALMA) to map Saturn's stratospheric zonal winds. We derive the zonal winds as a function of latitude from the Doppler shifts induced by the winds on the spatially and spectrally resolved spectral lines. In this paper, we will present and discuss our results.

How to cite: Cavalié, T., Benmahi, B., Fouchet, T., Moreno, R., Lellouch, E., Guerlet, S., Spiga, A., and Moullet, A.: First direct measurements of the zonal winds in Saturn's stratosphere, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-237, https://doi.org/10.5194/epsc2021-237, 2021.

EPSC2021-402
|
ECP
|
solicited
James Blake, Leigh Fletcher, Arrate Antunano, Henrik Melin, Mike Roman, Glenn Orton, Naomi Rowe-Gurney, Oliver King, and Mael Es-Sayeh

Abstract

Thermal-infrared imaging observations spanning more than three decades from the VISIR instrument on the VLT, COMICS on Subaru and archived observations from NASA IRTF are used to characterise Saturn’s seasonal changes. Radiative transfer modelling (using NEMESIS [8]) provides the northern hemisphere temperature progression of the atmosphere over 15 years (2005-2020), both during and beyond the Cassini mission. Comparisons with a record of temperature variability from Cassini/CIRS measurements [10] establish the ability to replicate ground-based observations with CIRS temperature and composition inputs to NEMESIS. Imaging observations taken one Saturn year apart (1989-2018) show the limited extent of the interannual variability of Saturn’s northern hemisphere climate. Further comparisons from VISIR observations in 2017 and COMICS in 2020 show the seasonal progression of Saturn since the demise of Cassini. We characterize the seasonal atmospheric temperature progression of Saturn over the course of a full Saturnian year for the first time.

Introduction

With the culmination of Cassini's unprecedented 13-year exploration of the Saturn system in September 2017, and with no future missions currently scheduled to visit the ringed world, the requirement to build on Cassini's discoveries now falls upon Earth-based observatories. Mid-infrared observations have been used to characterise features such as the extreme temperatures within an enormous storm system in 2011 [1,6], the cyclic variations in temperatures and winds associated with the 'Quasi-Periodic Oscillation' (QPO) in the equatorial stratosphere [2] and the onset of a seasonal warm polar vortex over the northern summer pole [3].

Saturn's axial tilt of 27º subjects its atmosphere to seasonal shifts in insolation [4], the effects of which are most significant at the gas giant's poles. The north pole emerged from northern spring equinox in 2009 (planetocentric solar longitude Ls=0º), and northern summer solstice in May 2017 (Ls=90º), providing Earth-based observers with their best visibility of the north polar region since 1987, with its warm central cyclone and long-lived hexagonal wave [5,6].

Studying these interconnected phenomena within Saturn's atmosphere (particularly those that evolve with time in a cyclic fashion) requires regular temporal sampling throughout Saturn's long 29.5-year orbit. We present here a showcase of research from the wealth of archived observations from VLT/VISIR and Subaru/COMICS since 2005, as well as infrared imagery obtained from NASA/IRTF throughout the 1980s.

1.1 Temperature progression

Methane (CH4) is used to determine stratospheric temperatures due to its even distribution across the planet. Figure 1 shows the changes in the stratospheric and tropospheric conditions as seen by VISIR over 3 years; these images are representative of a range of filters between 7-20 µm. We probe changes in the atmospheric 2D temperature brightness distribution across the planet disc in VISIR and COMICS observations taken from April 2005 (Ls=303.6º) to July 2020 (Ls=124.6º); thereby discerning the spatial variability as well as temporal (figure 2). VISIR observations concurrent with the Cassini/CIRS observations are used to cross-check the time-series from Cassini, which can be extended beyond the end-of-mission with the newer VISIR and COMICS observations. These profiles provide a new measure of long-term temperature variability in the context of an established model.

1.2 Interannual Variability

VISIR imaging from September 2017 have provided a unique opportunity, as they were acquired nearly one Saturn year apart from the 1989 observations of Gezari et al, (1989) [7], which were the first images of Saturn in the mid-IR to be taken with a 2D detector, rather than raster scanning. Examining the differences in brightness temperatures and composition indicate limited interannual variation for Saturn’s northern hemisphere (Figure 3). This also provides unique insight into the timescale of Saturn’s equatorial stratospheric oscillation which will be contrasted with a previously suggested biennial cycle [2]. The seasonal temperature progression measured in Section 1.1 also enables us to place this interannual variability in a wider context and provides further opportunity for insightful comparison with the comparatively shorter-term temperature variability.

Figure 1: VISIR observations from P95-102 sensing the troposphere (right) and stratosphere (left).  Polar warming is evident in the stratosphere; but is considerably smaller than that seen during southern summer and in the historical record of the 1980s.  The warm polar hexagon is seen at the north pole, the first such observation from the ground. Work to remove residual striping is ongoing and has been successfully applied to the 2017 images. 2015-16 images have been published by Fletcher et al., 2017 [2].

 

 

(a)

(b)

Figure 2: (a) The latitudinal brightness temperature progression of COMICS and VISIR ground-based observations from 2005 (dark blue) to 2017 (dark red), (b) the latitudinal brightness temperature progression of CIRS observations (from Fletcher et al, 2009) from 2005 (dark blue) to 2017 (dark red). 

Figure 3: A comparison of a latitudinal brightness temperature profile sampled from a 12.4µm observation (of Gezari et al. 1989) in red and a latitudinal bright temperature profile from a synthetic image generated using the temperatures and composition from CIRS observations in 2017 shown in black. The contrast between these profiles shows the degree of interannual variability at 12.4µm.

Acknowledgements

This research is funded by a European Research Council consolidated grant under the European Union’s Horizon 2020 research and innovation program, grant agreement 723890. We would like to thank co-author Mael Es-Sayeh for his significant contribution to this research.

References

[1] Fletcher et al., 2012, Icarus 221, p560-586

[2] Fletcher et al., 2017, Nature Astronomy, 1, p765-770

[3] Fletcher et al. 2015, Icarus. 251, 131-153

[4] Fletcher et al., 2015, https://arxiv.org/abs/1510.05690

[5] Fletcher et al., 2008, Science. 319, 79-81

[6] Fouchet et al., 2016, Icarus, 277, p196-214

[7] Gezari et al., 1989, Nature, 342, 777–780

[8] Irwin et al. 2008, JQSRT 109:1136-1150

[9] Orton et al., 2008, Nature 453, p198

[10] Fletcher et al. 2009, Icarus 200, 154-175

How to cite: Blake, J., Fletcher, L., Antunano, A., Melin, H., Roman, M., Orton, G., Rowe-Gurney, N., King, O., and Es-Sayeh, M.: Saturn’s Seasonal Atmosphere: Cassini CIRS contrasts to ground-based observations, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-402, https://doi.org/10.5194/epsc2021-402, 2021.

EPSC2021-408
Manuel López-Puertas, Alejandro Sánchez-López, Maya García-Comas, Bernd Funke, Thierry Fouchet, and Ignas Snellen

CH4 plays a key role in the thermal structure of Jupiter's upper atmosphere and hence knowing its vertical distribution is crucial for its understanding. Methane concentrations have been inferred previously from the analyses of solar occultation, He and Ly-α airglow, and the ISO/SWS radiance measurements around 3.3 µm, showing all rather different values, particularly around the homopause. Even different analyses of the same ISO/SWS radiance spectra yield very different CH4 volume mixing ratio profiles. Here, we present a new analysis of the ISO/SWS radiance spectra by using a comprehensive non-Local Thermodynamic Equilibrium (non-LTE) model and the most recent collisional rates measured in the laboratory. Further, we briefly discuss the potential effects of non-LTE on CH4 3.3 µm emission of temperate Jupiter exoplanets.

How to cite: López-Puertas, M., Sánchez-López, A., García-Comas, M., Funke, B., Fouchet, T., and Snellen, I.: CH4 abundance in Jupiter's upper atmosphere: A re-analysis of the ISO/SWS 3.3 µm non-LTE emission, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-408, https://doi.org/10.5194/epsc2021-408, 2021.

EPSC2021-551
Naiara Barrado-Izagirre, Jon Legarreta, Agustín Sánchez-Lavega, Santiago Pérez-Hoyos, Ricardo Hueso, Peio Iñurrigarro, Jose Felix Rojas, Iñaki Ordoñez-Etxeberria, and Iñigo Mendikoa

Jupiter’s atmosphere holds a large variety of vortices. In the transition region between the North Equatorial Band (NEBn) and North Tropical Zone (NTrZ) there are convective storms, cyclones and anticyclones at nearby latitudes and atmospheric waves. In this complex region there is a large anticyclone the North Tropical Oval (NTrO) located at 19ºN planetographic latitude that persists since at least 2006 and it is one of the longest-lived anticyclonic ovals in the planet, following the Great Red Spot and oval BA.

The NTrO has endured a complex dynamic history. It experienced one major merger with other oval in February 2013. It has also suffered color changes, with a change from white to red in September 2013 and then, in December 2014, back to white, but with a remaining external red ring. Moreover, it has survived major disturbances of the region. A North Temperate Belt Disturbance (NTBd) occurred in October 2016, which fully covered the oval, leaving it undistinguishable for months. When it reappeared, it was at the expected longitude from its previous longitudinal tracking with a similar appearance, a white large oval and same color and morphology from 2017 to 2021. It also survived the NTB disturbances that occurred in 2012 and 2020. In 2020 the region shows several other ovals in the vicinity so observations in 2021 will probably be able to show interactions between the NTrO and these new ovals.

To describe the historic evolution of this anticyclone we use JunoCam, Hubble Space Telescope (HST), IOPW database and PlanetCam-UPV/EHU multi-wavelength observations. We have retrieved a very complete track of the oval with major changes in its drift rate in specific periods of time. JunoCam and HST images have been used to measure its size and internal rotation obtaining a mean value of (10,500±1,000) x (5,800±600) km for the size and a mean relative vorticity of -(2±1)·10-5s-1. While GRS and BA have higher vorticity values than their environments, the NTrO’s vorticity is nearly the same as the ambient vorticity of its surroundings. This may suggest that this oval is probably sustained by the zonal jets confining it.

Using HST and PlanetCam observations, we have characterized its color changes measuring the color and altitude-opacity indices. The results obtained for these indices show that the oval is higher and has redder clouds than its environment but has lower cloud tops than other large ovals like the GRS, and it is less red than the GRS and oval BA.

Despite the external changes, including mergers and planetary-scale disturbances, and internal ones, in the form of morphology, altitude and color changes, none of them destroyed the vortex. The main characteristics of the oval remain unaltered. The drift rate and vorticity are visibly connected to its latitudinal location. The stability of the vortex to all the different changes of the area and its latitudinal changes suggest that the vortex is sustained by the atmosphere at levels much deeper than the observable cloud level.

How to cite: Barrado-Izagirre, N., Legarreta, J., Sánchez-Lavega, A., Pérez-Hoyos, S., Hueso, R., Iñurrigarro, P., Rojas, J. F., Ordoñez-Etxeberria, I., and Mendikoa, I.: Temporal evolution of the NTrO, the third largest oval on Jupiter, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-551, https://doi.org/10.5194/epsc2021-551, 2021.

EPSC2021-134
Arrate Antunano, Leigh N Fletcher, Glenn S Orton, Henrik Melin, Padraig T. Donnelly, Michael T Roman, James A Sinclair, and Yasumasa Kasaba

1. Overview

Jupiter's banded structure undergoes remarkable global-scale disturbances that can completely change its appearance from the deep troposphere below the cloud deck (2-7 bar) to the stratosphere (~1 mbar). These events can alter Jupiter's cloud structure, aerosols, and temperature field through mechanisms that are not well understood, and provide relevant insights into Jupiter’s time-variable atmospheric dynamics. Characterizing Jupiter's atmospheric changes in the long-term is crucial to better understand the origin and nature of the planetary scale disturbances, distinguishing between seasonal or mechanical forcing, and enables further investigation of the coupling of Jupiter's belts and zones that could explain the presence of 'Global Upheavals' (Rogers, 1995). In this study, we will describe how Jupiter's temperatures and aerosols vary over long spans of time, from the top NH3 clouds to the stable mid-stratosphere, and we will show that although Jupiter's troposphere and stratosphere exhibit a large number dynamical phenomena, there exists quasi-periodic patterns that may aid in future predictions of planetary-scale changes to the banded structure.

2. Ground-Based Observations

Continued monitoring of Jupiter from ground-based observatories from the past 40 years has provided an unprecedented resource for understanding the cyclic/non-cyclic environmental changes  in temperature, aerosols, and composition governing Jupiter’s dynamic atmosphere. More recently, ground-based observations have provided essential temporal, spectral and spatial resolution to support observations from the Juno spacecraft. Our study uses ground-based mid-infrared observations captured between 1983 and 2019 at wavelengths between 7.9 µm and 24.5 µm by 7 different instruments: the BOLO-1 (1983-1993), AT-1 (1983-1993), MIRAC (1993-1999), MIRLIN (1996-2003) and MIRSI (2003-2011) instruments mounted at the 3-m NASA Infrared Telescope Facility (IRTF) in Hawai'i; the VISIR (2006-2011, 2016-2018) instrument mounted at the 8-m Very Large Telescope (VLT) in Chile; and the COMICS (2005-2019) instrument on the 8-m Subaru Telescope in Hawai'i. Examples of Jupiter images at different wavelengths are given in Figure 1.

Figure 1. Examples of images of Jupiter captured by the MIRSI instrument at 7 different wavelengths.

3. Multi-Year Cycles of Variability

As mentioned above, Jupiter’s belts and zones endure dramatic global-scale changes over short-timescales, where belts expand, contract and even entirely disappear in a complex and turbulent way (e.g., Fletcher et al., 2017, doi:10.1002/2017GL073806). The most remarkable examples of this are the South Equatorial Belt (SEB, at 7°-17° S) fading and revival cycles (e.g., Sánchez-Lavega & Gomez, 1996, doi:10.1006/icar.1996.0067; Fletcher et al., 2017, doi:10.1016/j.icarus.2017.01.001), where the typically warm and dark belt at visible wavelengths transforms into a cold, cloud-covered whitish zone in timescales of months, remaining disturbed for years before energetic storms trigger the revival of the belt. A similar ‘revival’ process occurs semi-periodically at the North Temperate Belt (NTB, at 21°-28° N), where energetic convective storms rising from the water layer in the deep troposphere at this belt interact with the background flow producing a new low-albedo band over the southern half of the NTB (e.g., Sánchez-Lavega et al., 2017, doi: 10.1002/2017GL073421). At lower latitudes, the North Equatorial Belt (NEB, at 7°-17° N) is observed to expand northward in time intervals of 3 to 5 years, causing a gradual decrease in reflectivity (darkening) at the neighbouring North Tropical Zone (NTrZ, at 18°-21° N), typically originated from wave-like bulges of materials impinging on the NTrZ (e.g. Rogers, 1995; Fletcher et al., 2017, 10.1002/2017GL073383). Finally, Jupiter’s Equatorial Zone (EZ, within ±7° of the equator) experiences a rare 7-year cyclic disturbance, where the typically white (NH3 cloud-covered) and cold EZ displays a new 5-μm-bright (NH3 cloud-free) band encircling the planet south of the equator, accompanied by a reddish coloration at visible wavelengths (e.g., Antuñano et al., 2018, doi: 10.1029/2018GL080382; Rogers, 1995).

 

In this presentation, we will show zonal-mean brightness temperature maps spanning the period between 1983 and 2019 at 5 different wavelengths (7.9 µm, 8.6 µm, 10.7 µm, 18.7 µm and 20.5 µm) and between 1996 and 2019 at 8 wavelengths (same list plus 13.0 µm, 17.6 µm and 24.5 µm). We will describe the temporal and latitudinal variability of the brightness temperature at each of these wavelengths, looking for potential correlation/anticorrelation between changes at different belts that could help to reveal the processes underpinning the jovian global upheavals. We will also compare changes at different wavelengths to better understand the vertical extent of the global-scale disturbances in Jupiter’s banded structure.

4. Temperature and Aerosol Opacity: Variability

Zonal-mean radiance profiles at different wavelengths can be stacked together to form 5-point (7.9 µm, 8.6 µm, 10.7 µm, 18.7 µm and 20.5 µm) spectral image cubes between 1983 and 2019 and 8-point (the same plus 13.0 µm, 17.6 µm, and 24.5 µm) spectral image cubes between 1996 and 2019. These spectral image cubes can then be inverted independently using the radiative-transfer and retrieval code NEMESIS (Irwin et al., 2008, doi:10.1016/j.jqsrt.2007.11.006), to obtain crude estimations of stratospheric temperatures at 10-20 mbar (constrained by the 7.9 µm wavelength), upper-tropospheric (100-300 mbar) and mid-tropospheric (~500 mbar) temperatures (constrained by the 17.6 µm-24.5 µm and 10.7 µm, respectively), and tropospheric aerosol opacity at 400-600 mbar (constrained by the 8.6 µm wavelength).

 

Here, we will show stratospheric and tropospheric temperature and aerosol opacity maps between 1983 and 2019. We will describe the timescales of the variability observed in these maps by presenting a Lomb-Scargle analysis, and we will compare their periodicity to previously reported cyclic activity in Jupiter’s atmosphere, describing how temperature and aerosols vary during the planetary-scale disturbances. We will also compare the periodicity found at different belts, showing an NEB-SEB anticorrelation in the aerosol opacity and mid-tropospheric temperatures, and differences in the temperature field and aerosol opacity between hemispheres will be discussed. Finally, we will reveal a tropospheric-stratospheric coupling associated with Jupiter's Equatorial Stratospheric Oscillation. 

How to cite: Antunano, A., Fletcher, L. N., Orton, G. S., Melin, H., Donnelly, P. T., Roman, M. T., Sinclair, J. A., and Kasaba, Y.: Cycles of Variability in Jupiter's Atmosphere from Ground-Based Mid-Infrared Observations, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-134, https://doi.org/10.5194/epsc2021-134, 2021.

EPSC2021-667
Gerald Eichstädt, Candice Hansen, and Glenn Orton

 

Abstract

Traditionally, Jupiter's zonal wind profile is described as a function of latitude. Statistical data are integrated along circles of latitude. It is straightforward to apply the same principle to zonal vorticity profiles based on vorticity maps. This approach assumes implicitly a rotational symmetry of Jupiter's zonal structure with respect to Jupiter's rotation axis. However, the centers of both clusters of circumpolar cyclones turned out to be displaced from the respective pole. An appropriate description of zonal profiles requires a more flexible framework. This presentation is dedicated to a flexible geometrical way that a vorticity profile can be defined, as well as to the level of detail to which statistical data are described in the profile. The general approach is applicable well beyond zonal vorticity profiles, but our focus is on vorticity data retrieved from JunoCam [1] images.

 

Geometry

The circles of latitudes form a family of concentrical circles parameterized by the latitude as the only parameter. Let's call this parameter the “index” that is mapped to its circle of latitude. We obtain additional flexibility by a continuous distortion of the family of concentrical circles and by restricting the resulting family of curves to valid areas of interest without distorting our vorticity map. This generalized family of curves is sufficiently flexible to investigate profiles of 2-dimensional structures beyond zonal vorticity profiles. For even more flexibility in our evaluation, we can merge several such families of curves of the same index set into a single family of curves by concatenating corresponding curves.

A curve of the family is embedded into a vorticity map. So, each arc length position of the curve is mapped to a vorticity value.

 

Statistics

Rather than plotting a diagram of vorticity as a function of arc length, we are more interested in the statistical vorticity distribution covered by the respective curve of our family of curves. This construction induces a mapping that assigns each index a vorticity distribution function.

These vorticity distribution functions can be discussed as they are, or they are reduced to usual statistical parameters such as the mean, standard deviation, or higher-order statistical moments. Profiles as a function of our index can be plotted as diagrams when based on such statistical parameters.

 

Modified Zonal Vorticity Profile

With these general considerations, we return to our initial motivation: A modification of a zonal vorticity profile (ZVP) based on a modified pole close to the center of the south polar cyclone with modified circles of latitude continuously approximating the traditional definition of circles of latitude for lower latitudes.