1
|
Moses JI, Cavalié T, Fletcher LN, Roman MT. Atmospheric chemistry on Uranus and Neptune. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20190477. [PMID: 33161866 PMCID: PMC7658780 DOI: 10.1098/rsta.2019.0477] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 06/16/2020] [Indexed: 05/04/2023]
Abstract
Comparatively little is known about atmospheric chemistry on Uranus and Neptune, because remote spectral observations of these cold, distant 'Ice Giants' are challenging, and each planet has only been visited by a single spacecraft during brief flybys in the 1980s. Thermochemical equilibrium is expected to control the composition in the deeper, hotter regions of the atmosphere on both planets, but disequilibrium chemical processes such as transport-induced quenching and photochemistry alter the composition in the upper atmospheric regions that can be probed remotely. Surprising disparities in the abundance of disequilibrium chemical products between the two planets point to significant differences in atmospheric transport. The atmospheric composition of Uranus and Neptune can provide critical clues for unravelling details of planet formation and evolution, but only if it is fully understood how and why atmospheric constituents vary in a three-dimensional sense and how material coming in from outside the planet affects observed abundances. Future mission planning should take into account the key outstanding questions that remain unanswered about atmospheric chemistry on Uranus and Neptune, particularly those questions that pertain to planet formation and evolution, and those that address the complex, coupled atmospheric processes that operate on Ice Giants within our solar system and beyond. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.
Collapse
Affiliation(s)
- J. I. Moses
- Space Science Institute, 4765 Walnut Street, Suite B, Boulder, CO 80301, USA
| | - T. Cavalié
- Laboratoire d’Astrophysique de Bordeaux, University of Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
- LESIA, Observatoire de Paris, 92195 Meudon, France
| | - L. N. Fletcher
- School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
| | - M. T. Roman
- School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
| |
Collapse
|
2
|
Léard P, Lecoanet D, Le Bars M. Multimodal Excitation to Model the Quasibiennial Oscillation. PHYSICAL REVIEW LETTERS 2020; 125:234501. [PMID: 33337230 DOI: 10.1103/physrevlett.125.234501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Accepted: 10/19/2020] [Indexed: 06/12/2023]
Abstract
The quasibiennial oscillation (QBO) of stratospheric winds is the most striking example of mean-flow generation and reversal by the nonlinear interactions of internal waves. Previous studies have used an idealized monochromatic forcing to investigate the QBO. Here we instead force a more realistic continuous wave spectrum. Unexpectedly, spreading the wave energy across a wide frequency range leads to more regular oscillations. We also find that different forcing spectra can yield the same QBO. Multimodal wave forcing is thus essential for understanding wave-mean-flow interactions in nature.
Collapse
Affiliation(s)
- P Léard
- Aix Marseille Université, CNRS, Centrale Marseille, IRPHE, Marseille 13013, France
| | - D Lecoanet
- Northwestern University, Engineering Sciences and Applied Mathematics, Evanston, Illinois 60208, USA
| | - M Le Bars
- Aix Marseille Université, CNRS, Centrale Marseille, IRPHE, Marseille 13013, France
| |
Collapse
|
3
|
Ingersoll AP. Cassini Exploration of the Planet Saturn: A Comprehensive Review. SPACE SCIENCE REVIEWS 2020; 216:122. [PMID: 35027776 PMCID: PMC8753610 DOI: 10.1007/s11214-020-00751-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Accepted: 10/10/2020] [Indexed: 06/14/2023]
Abstract
Before Cassini, scientists viewed Saturn's unique features only from Earth and from three spacecraft flying by. During more than a decade orbiting the gas giant, Cassini studied the planet from its interior to the top of the atmosphere. It observed the changing seasons, provided up-close observations of Saturn's exotic storms and jet streams, and heard Saturn's lightning, which cannot be detected from Earth. During the Grand Finale orbits, it dove through the gap between the planet and its rings and gathered valuable data on Saturn's interior structure and rotation. Key discoveries and events include: watching the eruption of a planet-encircling storm, which is a 20- or 30-year event, detection of gravity perturbations from winds 9000 km below the tops of the clouds, demonstration that eddies are supplying energy to the zonal jets, which are remarkably steady over the 25-year interval since the Voyager encounters, re-discovery of the north polar hexagon after 25 years, determination of elemental abundance ratios He/H, C/H, N/H, P/H, and As/H, which are clues to planet formation and evolution, characterization of the semiannual oscillation of the equatorial stratosphere, documentation of the mysteriously high temperatures of the thermosphere outside the auroral zone, and seeing the strange intermittency of lightning, which typically ceases to exist on the planet between outbursts every 1-2 years. These results and results from the Jupiter flyby are all discussed in this review.
Collapse
Affiliation(s)
- Andrew P Ingersoll
- Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Blvd, Pasadena, CA 91125, USA
| |
Collapse
|
4
|
Semin B, Garroum N, Pétrélis F, Fauve S. Nonlinear saturation of the large scale flow in a laboratory model of the quasibiennial oscillation. PHYSICAL REVIEW LETTERS 2018; 121:134502. [PMID: 30312087 DOI: 10.1103/physrevlett.121.134502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Revised: 07/26/2018] [Indexed: 06/08/2023]
Abstract
The quasibiennial oscillation (QBO) is the nearly periodic reversal of the large scale flow generated by internal waves in the equatorial stratosphere. Using a laboratory model experiment, we study the instability that generates the QBO and investigate its nonlinear regime. We report the first quantitative measurements of the nonlinearly saturated velocity of the flow. We show that the QBO is generated by a bifurcation that is either supercritical or subcritical depending on the dominant dissipative process. This is confirmed by a nonlinear analysis in the vicinity of the instability threshold.
Collapse
Affiliation(s)
- B Semin
- Laboratoire de Physique Statistique, École Normale Supérieure, PSL Research University, Université Paris Diderot Sorbonne Paris-Cité, Sorbonne Universités UPMC, Univ Paris 06, and CNRS, 24 rue Lhomond, 75005 Paris, France
| | - N Garroum
- Laboratoire de Physique Statistique, École Normale Supérieure, PSL Research University, Université Paris Diderot Sorbonne Paris-Cité, Sorbonne Universités UPMC, Univ Paris 06, and CNRS, 24 rue Lhomond, 75005 Paris, France
| | - F Pétrélis
- Laboratoire de Physique Statistique, École Normale Supérieure, PSL Research University, Université Paris Diderot Sorbonne Paris-Cité, Sorbonne Universités UPMC, Univ Paris 06, and CNRS, 24 rue Lhomond, 75005 Paris, France
| | - S Fauve
- Laboratoire de Physique Statistique, École Normale Supérieure, PSL Research University, Université Paris Diderot Sorbonne Paris-Cité, Sorbonne Universités UPMC, Univ Paris 06, and CNRS, 24 rue Lhomond, 75005 Paris, France
| |
Collapse
|
5
|
Sánchez-Lavega A, García-Melendo E, Pérez-Hoyos S, Hueso R, Wong MH, Simon A, Sanz-Requena JF, Antuñano A, Barrado-Izagirre N, Garate-Lopez I, Rojas JF, Del Río-Gaztelurrutia T, Gómez-Forrellad JM, de Pater I, Li L, Barry T. An enduring rapidly moving storm as a guide to Saturn's Equatorial jet's complex structure. Nat Commun 2016; 7:13262. [PMID: 27824031 PMCID: PMC5105178 DOI: 10.1038/ncomms13262] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2015] [Accepted: 09/16/2016] [Indexed: 11/09/2022] Open
Abstract
Saturn has an intense and broad eastward equatorial jet with a complex three-dimensional structure mixed with time variability. The equatorial region experiences strong seasonal insolation variations enhanced by ring shadowing, and three of the six known giant planetary-scale storms have developed in it. These factors make Saturn's equator a natural laboratory to test models of jets in giant planets. Here we report on a bright equatorial atmospheric feature imaged in 2015 that moved steadily at a high speed of 450 ms-1 not measured since 1980-1981 with other equatorial clouds moving within an ample range of velocities. Radiative transfer models show that these motions occur at three altitude levels within the upper haze and clouds. We find that the peak of the jet (latitudes 10° N to 10° S) suffers intense vertical shears reaching +2.5 ms-1 km-1, two orders of magnitude higher than meridional shears, and temporal variability above 1 bar altitude level.
Collapse
Affiliation(s)
- A Sánchez-Lavega
- Departamento Física Aplicada I, Universidad del País Vasco UPV/EHU, Escuela de Ingeniería de Bilbao, Alameda Urquijo s/n, 48013 Bilbao, Spain
| | - E García-Melendo
- Departamento Física Aplicada I, Universidad del País Vasco UPV/EHU, Escuela de Ingeniería de Bilbao, Alameda Urquijo s/n, 48013 Bilbao, Spain.,Fundació Observatori Esteve Duran, c/ Montseny, 46-Urb. El Montanyá, Seva 08553, Barcelona, Spain
| | - S Pérez-Hoyos
- Departamento Física Aplicada I, Universidad del País Vasco UPV/EHU, Escuela de Ingeniería de Bilbao, Alameda Urquijo s/n, 48013 Bilbao, Spain
| | - R Hueso
- Departamento Física Aplicada I, Universidad del País Vasco UPV/EHU, Escuela de Ingeniería de Bilbao, Alameda Urquijo s/n, 48013 Bilbao, Spain
| | - M H Wong
- University of California, Department of Astronomy, 501 Campbell Hall, Berkeley, California 94720, USA
| | - A Simon
- NASA Goddard Space Flight Center/690, 8800 Greenbelt Road, Greenbelt, Maryland 20771, USA
| | - J F Sanz-Requena
- Universidad Europea Miguel de Cervantes, Departamento de Ciencias Experimentales, C/Padre Julio Chevalier, 2, 47012 Valladolid, Spain
| | - A Antuñano
- Departamento Física Aplicada I, Universidad del País Vasco UPV/EHU, Escuela de Ingeniería de Bilbao, Alameda Urquijo s/n, 48013 Bilbao, Spain
| | - N Barrado-Izagirre
- Departamento Física Aplicada I, Universidad del País Vasco UPV/EHU, Escuela de Ingeniería de Bilbao, Alameda Urquijo s/n, 48013 Bilbao, Spain
| | - I Garate-Lopez
- Departamento Física Aplicada I, Universidad del País Vasco UPV/EHU, Escuela de Ingeniería de Bilbao, Alameda Urquijo s/n, 48013 Bilbao, Spain
| | - J F Rojas
- Departamento Física Aplicada I, Universidad del País Vasco UPV/EHU, Escuela de Ingeniería de Bilbao, Alameda Urquijo s/n, 48013 Bilbao, Spain
| | - T Del Río-Gaztelurrutia
- Departamento Física Aplicada I, Universidad del País Vasco UPV/EHU, Escuela de Ingeniería de Bilbao, Alameda Urquijo s/n, 48013 Bilbao, Spain
| | - J M Gómez-Forrellad
- Fundació Observatori Esteve Duran, c/ Montseny, 46-Urb. El Montanyá, Seva 08553, Barcelona, Spain
| | - I de Pater
- University of California, Department of Astronomy, 501 Campbell Hall, Berkeley, California 94720, USA
| | - L Li
- Department of Physics, University of Houston, Houston, Texas 77204, USA
| | - T Barry
- Broken Hill Observatory, 406 Bromide Street, Broken Hill, New South Wales 2880, Australia
| |
Collapse
|
6
|
Godin OA. Diffraction of acoustic-gravity waves in the presence of a turning point. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2016; 140:283. [PMID: 27475153 DOI: 10.1121/1.4955283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Acoustic-gravity waves (AGWs) in an inhomogeneous atmosphere often have caustics, where the ray theory predicts unphysical, divergent values of the wave amplitude and needs to be modified. Unlike acoustic waves and gravity waves in incompressible fluids, AGW fields in the vicinity of a caustic have never been systematically studied. Here, asymptotic expansions of acoustic gravity waves are derived in the presence of a turning point in a horizontally stratified, moving fluid such as the atmosphere. Sound speed and the background flow (wind) velocity are assumed to vary gradually with height, and slowness of these variations determines the large parameter of the problem. It is found that uniform asymptotic expansions of the wave field in the presence of a turning point can be expressed in terms of the Airy function and its derivative. The geometrical, or Berry, phase, which arises in the consistent Wentzel-Kramers-Brillouin approximation for AGWs, plays an important role in the caustic asymptotics. In the dominant term of the uniform asymptotic solution, the terms with the Airy function and its derivative are weighted by the cosine and sine of the Berry phase, respectively. The physical meaning and corollaries of the asymptotic solutions are discussed.
Collapse
Affiliation(s)
- Oleg A Godin
- Department of Physics, Naval Postgraduate School, Monterey, California 93943-5216, USA
| |
Collapse
|
7
|
Moses JI, Armstrong ES, Fletcher LN, Friedson AJ, Irwin PGJ, Sinclair JA, Hesman BE. Evolution of Stratospheric Chemistry in the Saturn Storm Beacon Region. ICARUS 2015; 261:149-168. [PMID: 30842685 PMCID: PMC6398963 DOI: 10.1016/j.icarus.2015.08.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The giant northern-hemisphere storm that erupted on Saturn in December 2010 triggered significant changes in stratospheric temperatures and species abundances that persisted for more than a year after the original outburst. The stratospheric regions affected by the storm have been nicknamed "beacons" due to their prominent infrared-emission signatures (Fletcher, L.N. et al. [2011]. Science 332, 1413). The two beacon regions that were present initially merged in April 2011 to form a single, large, anticyclonic vortex (Fletcher, L.N. et al. [2012]. Icarus 221, 560). We model the expected photochemical evolution of the stratospheric constituents in the beacons from the initial storm onset through the merger and on out to March 2012. The results are compared with longitudinally resolved Cassini/CIRS spectra from May 2011. If we ignore potential changes due to vertical winds within the beacon, we find that C2H2, C2H6, and C3H8 remain unaffected by the increased stratospheric temperatures in the beacon, the abundance of the shorter-lived CH3C2H decreases, and the abundance of C2H4 increases significantly due to the elevated temperatures, the latter most notably in a secondary mixing-ratio peak located near mbar pressures. The C4H2 abundance in the model decreases by a factor of a few in the 0.01-10 mbar region but has a significant increase in the 10-30 mbar region due to evaporation of the previously condensed phase. The column abundances of C6H6 and H2O above ~30 mbar also increase due to aerosol evaporation. Model-data comparisons show that models that consider temperature changes alone underpredict the abundance of C2H x species by a factor of 2-7 in the beacon core in May 2011, suggesting that other processes not considered by the models, such as downwelling winds in the vortex, are affecting the species profiles. Additional calculations indicate that downwelling winds of order -10 cm s -1 near ~0.1 mbar need to be included in the photochemical models in order to explain the inferred C2H x abundances in the beacon core, indicating that both strong subsiding winds and chemistry at elevated temperatures are affecting the vertical profiles of atmospheric constituents in the beacon. We (i) discuss the general chemical behavior of stratospheric species in the beacon region, (ii) demonstrate how the evolving beacon environment affects the species vertical profiles and emission characteristics (both with and without the presence of vertical winds), (iii) make predictions with respect to compositional changes that can be tested against Cassini and Herschel data, and higher-spectral-resolution ground-based observations of the beacon region, and (iv) discuss future measurements and modeling that could further our understanding of the dynamical origin, evolution, and chemical processing within these unexpected stratospheric vortices that were generated after the 2010 convective event.
Collapse
Affiliation(s)
- Julianne I Moses
- Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA
| | - Eleanor S Armstrong
- Atmospheric, Oceanic & Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK
| | - Leigh N Fletcher
- Atmospheric, Oceanic & Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK
| | | | - Patrick G J Irwin
- Atmospheric, Oceanic & Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK
| | - James A Sinclair
- Atmospheric, Oceanic & Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK
| | - Brigette E Hesman
- Department of Astronomy, University of Maryland, College Park, MD, 20742, USA
| |
Collapse
|
8
|
Li L, Achterberg RK, Conrath BJ, Gierasch PJ, Smith MA, Simon-Miller AA, Nixon CA, Orton GS, Flasar FM, Jiang X, Baines KH, Morales-Juberías R, Ingersoll AP, Vasavada AR, Del Genio AD, West RA, Ewald SP. Strong temporal variation over one Saturnian year: from Voyager to Cassini. Sci Rep 2013; 3:2410. [PMID: 23934437 PMCID: PMC3740281 DOI: 10.1038/srep02410] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Accepted: 07/22/2013] [Indexed: 11/09/2022] Open
Abstract
Here we report the combined spacecraft observations of Saturn acquired over one Saturnian year (~29.5 Earth years), from the Voyager encounters (1980-81) to the new Cassini reconnaissance (2009-10). The combined observations reveal a strong temporal increase of tropic temperature (~10 Kelvins) around the tropopause of Saturn (i.e., 50 mbar), which is stronger than the seasonal variability (~a few Kelvins). We also provide the first estimate of the zonal winds at 750 mbar, which is close to the zonal winds at 2000 mbar. The quasi-consistency of zonal winds between these two levels provides observational support to a numerical suggestion inferring that the zonal winds at pressures greater than 500 mbar do not vary significantly with depth. Furthermore, the temporal variation of zonal winds decreases its magnitude with depth, implying that the relatively deep zonal winds are stable with time.
Collapse
Affiliation(s)
- Liming Li
- University of Houston, Houston, TX, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
9
|
Affiliation(s)
- Tamas I. Gombosi
- Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI 48109, USA
| | - Andrew P. Ingersoll
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
| |
Collapse
|
10
|
|