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Cited by 110Astro and Planetary ScienceIonosphere and magnetosphere dynamicsStellar, planetary, and galactic studies

The DOI matches its Crossref record; 36 of the 36 references it cites were found in a registry or an index; none of the 26 sources its claims cite is checked for support yet.

Cassini imaging of Saturn: Southern hemisphere winds and vortices

Open access
Vasavada, A. R., Hörst, S. M., Kennedy, M. R., Ingersoll, A. P., Porco, C. C., Del Genio, A. D., West, R. A.·2006·Journal of Geophysical Research: Planets
DOI 10.1029/2005je002563
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Abstract

High‐resolution images of Saturn's southern hemisphere acquired by the Cassini Imaging Science Subsystem between February and October 2004 are used to create maps of cloud morphology at several wavelengths, to derive zonal winds, and to characterize the distribution, frequency, size, morphology, color, behavior, and lifetime of vortices. Nonequatorial wind measurements display only minor differences from those collected since 1981 and reveal a strong, prograde flow near the pole. The region just southward of the velocity minimum at 40.7°S is especially active, containing numerous vortices, some generated in the proximity of convective storms. The two eastward jets nearest the pole display periodicity in their longitudinal structure, but no direct analogs to the northern hemisphere's polar hexagon or ribbon waves were observed. Characteristics of winds and vortices are compared with those of Saturn's northern hemisphere and Jupiter's atmosphere.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

Cassini ISS images of Saturn's southern hemisphere from February–October 2004 are used to map cloud morphology, derive zonal winds, and survey vortices. The study finds a strong prograde polar flow, numerous vortices concentrated near westward jets and convective storms, and no southern analog to the northern polar hexagon.

Key findings

  • A total of 458 zonal wind measurements were made: 347 from the high-resolution maps and 111 from the approach maps. The eastward jet near 49.5°S was ~20 m s⁻¹ slower than in Voyager/HST comparisons, while the jet near 60.5°S was 35 m s⁻¹ faster; the latitude discrepancy for the 74.5°S jet was not understood.
  • Poleward of ~84°S, wind measurements were all eastward but varied between 0 and 140 m s⁻¹; tracking the asymmetric bright ring at 88.8°S gave 80–135 m s⁻¹, with ambiguity between ambient flow and wave phase speed.
  • The high-resolution maps contained 138 vortices, compared with only ~65 in the final approach maps. In the approach movie, 123 vortices were tracked, with 24 vortex-vortex mergers and 60 disappearances; 91 were initially detected after the first approach map.
  • Vortex lifetime correlated positively with size: 11 long-lived nonmerging vortices ranged from 1300 to 4500 km in diameter, while 33 short-lived vortices were all <1100 km. The largest observed vortex was 4500 km at 51.8°S.

Methods

  • Two Cassini ISS narrow-angle image sets were used: global multispectral approach mosaics from 6 February to 12 May 2004, with resolution improving from 425 to 155 km pixel⁻¹, and first-revolution mosaics from 6 September to 15 October 2004, with resolution improving from 53.2 to 27.9 km pixel⁻¹. Wind measurements used a pair of high-resolution maps from 18–19 September 2004 at 49.6 km pixel⁻¹.
  • Images were navigated, mapped to cylindrical and polar stereographic projections, and illumination-corrected with a high-pass filter. Cloud features were tracked by eye using custom IDL software; vortices were manually measured and classified into dark, dark with bright margin, bright-centered, and bright families.
  • Vortex tracking used the approach movie, requiring a vortex to appear in three consecutive approach maps or both high-resolution maps; trajectories, mergers, detections, disappearances, and lifetimes were analyzed.

Limitations

  • The paper states that vertical structure, aerosol properties, opacity, equatorial dynamics, and convective storm dynamics are left to other studies; it cannot determine whether tracked cloud features lie in a tropospheric haze or ammonia cloud layer. Direct measurement of tangential velocity within vortices proved difficult, and the sense of rotation was inferred only indirectly.
  • The paper notes that zonal velocity differences from Voyager/HST cannot confidently be said to exceed errors from different authors, data sets, techniques, and tracers; high-latitude measurements may refer to ambient flow or wave phase speed; approach maps cannot accurately count vortices <1000 km or reveal total number evolution; some initial detections may reflect increasing resolution rather than real vortex creation; lifetimes are lower limits; and the relevance of the barotropic stability criterion is unclear without knowledge of deep winds.
  • Evident from the text: coverage was biased toward the southern hemisphere, with the northern hemisphere obscured by geometry, rings, shadows, and low seasonal illumination; data gaps affected some maps and vortex tracking; manual feature tracking and high-pass filtering introduce subjectivity and lose some latitudinal albedo variation.

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Integrity signals

Registry

Crossref · 10.1029/2005je002563

Cites

36 of 36 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

0 of 26 cited sources checked · 0 supported · 0 flagged

Show all 117 claims

  • It may state two separate claims as one. 53
  • The quote only partly states this claim. 1
  • Probably not a substantial claim. 24
72 of 72

  • The paper relies on this without support.

    Cloud features tracked in the images move with the ambient zonal wind (i.e., are passive tracers).

    “We measured the latitudinal profile of zonal wind by tracking the displacement of cloud features on the pair of HRMs.”
    “Tracked features include discrete clouds and long-lived morphological features (e.g., kinks) within cloud bands or streaks.”

  • The paper relies on this without support.

    The vortex families based on brightness and morphology at 750 nm correspond to distinct dynamical types.

    “We have attempted to classify vortices into families based on their brightness and morphology at 750 nm (CB2 filter).”

  • The authors state this as an assumption.

    The sense of rotation of vortices can be inferred from the shear in which they are embedded.

    “their sense of rotation may be inferred (though not definitively) from the shear in which they are embedded.”

  • The paper relies on this without support.

    The barotropic stability criterion for two-dimensional flow is applicable to Saturn's jets despite deep winds.

    “In the framework of two-dimensional flow, jets are stable to barotropic instabilities when their curvature is less than b.”

  • The paper relies on this without support.

    The measured zonal wind profile at cloud level represents the ambient wind at the vortex latitudes.

    “In all cases the instantaneous drift rate was indistinguishable from the zonal wind speed at the latitude corresponding to the vortex center.”

  • The paper relies on this without support.

    The spectral coverage within the HRM data set can be used to make qualitative statements about the vertical structure of vortex types.

    “We can use the spectral coverage within the HRM data set to make some qualitative statements about the vertical structure of the vortex types described above (also see a similar discussion in section 3).”

  • The paper relies on this without support.

    The spectral patterns observed at different wavelengths indicate vertical structure of vortices.

    “This pattern suggests upwelling and/or upward displacement of horizontal flow at higher levels, a phenomena that is associated with larger anticyclones (nominally highpressure centers).”

  • The paper relies on this without support.

    The vortex types named according to CB2 appearance are the same features across wavelengths.

    “Note that the vortex types are named according to their appearance in CB2 images.”

  • The authors state this as an assumption.

    The largest vortex at 51.8°S has cyclonic vorticity.

    “This spectral pattern is consistent with its presumed cyclonic vorticity (i.e., that it is a low-pressure center, with downwelling at higher levels).”

  • The paper relies on this without support.

    Features on Saturn are harder to detect than features on Jupiter.

    “with the caveat that features on Saturn are harder to detect”

  • The paper relies on this without support.

    The relatively sparse appearance of Saturn compared with Jupiter is not solely due to detection difficulty.

    “A significant difference is the abundance of vortices and other dynamical features on Jupiter, compared with the relatively sparse appearance of Saturn (with the caveat that features on Saturn are harder to detect).”
11 of 11

Claims other papers make about this one

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Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Unclassified vortex count does not match the listed vortices

    Minor

    The listed unclassified vortices total seven: the largest vortex, two merging vortices, two at 76.4°S, and two with unique morphologies. The text says there are six.

  • Figure 1 caption points to a wind plot for the omitted polar region

    Minor

    The caption says the omitted polar latitudes are shown in Figure 4, but Figure 4 is a wind-measurement plot; Figure 2 is the polar map.

2 of 2

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  1. Ingersoll A. P., 1984, Saturn, 195

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Metadata

Authors
Vasavada, A. R., Hörst, S. M., Kennedy, M. R., Ingersoll, A. P., Porco, C. C., Del Genio, A. D., & West, R. A.
Affiliations
  • Jet Propulsion Laboratory (US)
  • Arizona State University (US)
  • California Institute of Technology (US)
  • Space Science Institute (US)
  • NASA Goddard Institute for Space Studies New York New York USA
ORCID
Venue
Journal of Geophysical Research: Planets
Publisher
American Geophysical Union (AGU)
Published
2006-05
Volume
111
Issue
E5
ISSN
0148-0227 (ISSN-L)
DOI
10.1029/2005je002563
OpenAlex
W2167521299
Semantic Scholar
2ddcd173db2d90abb6d99affd0c4251a3981677d
Cited by
110
References
36
Citations by year
2026: 5 · 2025: 5 · 2024: 2 · 2023: 1 · 2022: 4 · 2021: 5 · 2020: 9 · 2019: 3 · 2018: 12 · 2017: 8 · 2016: 8 · 2015: 7 · 2014: 1 · 2013: 6 · 2012: 3
FWCI
3.63
Type
journal article
Language
en
Open access
Licence
onlinelibrary.wiley.com/termsAndConditions#vor (vor, 18 d)
Locations
  • Journal of Geophysical Research Atmospheres (publishedVersion)
  • CaltechAUTHORS (California Institute of Technology) (submittedVersion)
Funders
  • National Aeronautics and Space Administration
  • California Institute of Technology
  • Jet Propulsion Laboratory
Topics
  • Physical Sciences › Earth and Planetary Sciences › Space and Planetary Science › Astro and Planetary Science
  • Physical Sciences › Earth and Planetary Sciences › Space and Planetary Science › Ionosphere and magnetosphere dynamics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
Keywords
Saturn, Southern Hemisphere, zonal wind, atmospheric vortices, cloud morphology, polar vortex, convective storms, Cassini imaging

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