Large-scale storms in Saturn's atmosphere during 1994

Science

Volumn 271, Issue 5249, 1996, Pages 631-634

  Sanchez Lavega, A ^a   Lecacheux, J ^b   Gomez, J M ^c   Colas, F ^d   Laques, P ^e   Noll, K ^f   Gilmore, D ^f   Miyazaki, I ^g   Parker, D ^h  

^a UNIVERSITY OF THE BASQUE COUNTRY UPV EHU   (Spain)

^b OBSERVATOIRE DE PARIS   (France)

^c Grup d'Estudis Astronomics   (Spain)

^d Bureau des Longitudes   (France)

^e OBSERVATOIRE MIDI PYRÉNÉES   (France)

^f AURA for the European Space Agency   (United States)

^g Oriental Astronomical Association   (Japan)

^h Assoc Lunar and Planet Observers   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0000665957     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.271.5249.631     Document Type: Article

References (31)

1. A. F. Alexander, The Planet Saturn (Faber and Faber, London, 1962).
2. A. Sanchez-Lavega, Icarus 44, 1 (1982).
3. A. P Ingersoll, R. F Beebe, B. J Conrath, G. E. Hunt, in Saturn, T. Gehrels and M S. Matthews, Eds (Univ. of Arizona Press, Tucson, 1984), pp. 195-238.
4. A Sanchez-Lavega and E. Battaner, Astron. Astrophys. 185, 315 (1987).
5. A Sanchez-Lavega, Chaos 4, 341 (1994)
6. A Sanchez-Lavega et al., Nature 353, 397 (1991).
7. R F. Beebe, C. D. Bamet, P. V Sada, A. S Murrel, Icarus 96, 163 (1992).
8. C. D Bamet. J A Westphal, R. F. Beebe, L. F. Huber, ibid 100, 499 (1992).
9. J A. Westphal et al., ibid., p. 485.
10. A Sanchez-Lavega, J. Lecacheux, F. Colas, P. Laques, J. Geophys Res. 98, 18857 (1993).
11. A. Sanchez-Lavega, J. M. Gomez, J. Lecacheux, F. Colas, I. Miyazaki, IAU Circ. No 6079 (1994)
12. J. M. Gomez, J Caquel, P. Laques, IAU Circ No. 6059 (1994).
13. Most images were taken through filter I (Table 1), which is sensitive to high-altitude hazes. Image processing methods were similar to those described by A. Sanchez-Lavega, J. Lecacheux, F. Colas, and P. Laques [Science 260, 329 (1993)] For morphology studies, we used an unsharp-mask image processing technique that consists of creating a degraded image from the original one and making an intermediate image from their subtraction. Using some calibration constants, it is possible to obtain a final image that is well contrasted on all parts of the planetary disk up to its edges. This treatment is efficient in discriminating fine features of low contrast.
14. Longitudes and zonal wind velocities are measured relative to the System III rotation rate (period = 10 hours and 39 4 mm), which is presumed to be that of the planet's magnetic field linked to the planet's interior [M. D. Desch and M. L Kaiser, Geophys. Res. Lett. 8, 253 (1981)].
15. A seasonal radiative-dynamic model of Saturn's troposphere suggests temporal changes in wind speeds within the equatorial region (30°N to 30°S), mainly as a result of ring shadowing and Saturn's tilt [C. D. Barnet, R F. Beebe, B. J. Conrath, Icarus 98, 94 (1992)].
16. R = 27,000 to 33,000 km, comparable with the longitudinal size of WS
17. R = 27,000 to 33,000 km, comparable with the longitudinal size of WS
18. R = 27,000 to 33,000 km, comparable with the longitudinal size of WS
19. R = 27,000 to 33,000 km, comparable with the longitudinal size of WS
20. Standard photometric reduction procedures were applied to the Pic-du-Midi images Flux calibration in the 300- to 1000-nm spectral region was performed on a beam 2 arc sec in diameter on the center of the disk with the use of recently measured reflectivities [E. Karkoschka and M. G. Tomasko, Icarus 106, 428 (1993); E Karkoschka, ibid 111, 174 (1994)) For the 261 -nm filter, we used absolute reflectivity measurements presented by R. A West et al. [J. Geophys. Res. 88, 8679 (1983)]. In the 2000- to 2140-nm spectral range, we used the absolute reflectivities of R N. Clark and T. B. McCord [Icarus 40, 180 (1979)]
21. Standard photometric reduction procedures were applied to the Pic-du-Midi images Flux calibration in the 300- to 1000-nm spectral region was performed on a beam 2 arc sec in diameter on the center of the disk with the use of recently measured reflectivities [E. Karkoschka and M. G. Tomasko, Icarus 106, 428 (1993); E Karkoschka, ibid 111, 174 (1994)) For the 261 -nm filter, we used absolute reflectivity measurements presented by R. A West et al. [J. Geophys. Res. 88, 8679 (1983)]. In the 2000- to 2140-nm spectral range, we used the absolute reflectivities of R N. Clark and T. B. McCord [Icarus 40, 180 (1979)]
22. Standard photometric reduction procedures were applied to the Pic-du-Midi images Flux calibration in the 300- to 1000-nm spectral region was performed on a beam 2 arc sec in diameter on the center of the disk with the use of recently measured reflectivities [E. Karkoschka and M. G. Tomasko, Icarus 106, 428 (1993); E Karkoschka, ibid 111, 174 (1994)) For the 261 -nm filter, we used absolute reflectivity measurements presented by R. A West et al. [J. Geophys. Res. 88, 8679 (1983)]. In the 2000- to 2140-nm spectral range, we used the absolute reflectivities of R N. Clark and T. B. McCord [Icarus 40, 180 (1979)]
23. Standard photometric reduction procedures were applied to the Pic-du-Midi images Flux calibration in the 300- to 1000-nm spectral region was performed on a beam 2 arc sec in diameter on the center of the disk with the use of recently measured reflectivities [E. Karkoschka and M. G. Tomasko, Icarus 106, 428 (1993); E Karkoschka, ibid 111, 174 (1994)) For the 261 -nm filter, we used absolute reflectivity measurements presented by R. A West et al. [J. Geophys. Res. 88, 8679 (1983)]. In the 2000- to 2140-nm spectral range, we used the absolute reflectivities of R N. Clark and T. B. McCord [Icarus 40, 180 (1979)]
24. A Sanchez-Lavega, J. Lecacheux, F. Colas, P. Laques, Icarus 108, 158 (1994) A Lambert surface of reflectivity A is one that reflects A times the flux incident on it in such a way that the reflected intensity is independent of the direction to the observer.
25. The scale height is defined as H = RT/μg, where R is the gas constant, T is the temperature, and μ is the mean molecular weight of the atmosphere In Saturn's troposphere, H ≈ 45 km. The tracers used to measure the Voyager velocities are assumed to have been measured at an average pressure of 400 mbar (20).
26. M. G. Tomasko, R. A. West, G. S. Orton, V. G Tejfel, in Saturn, T. Gehrels and M S. Matthews, Eds. (Univ. of Arizona Press, Tucson, 1984), pp. 150-194; E. Karkoshka and M. G. Tomasko, Icarus 97, 161 (1992)
27. M. G. Tomasko, R. A. West, G. S. Orton, V. G Tejfel, in Saturn, T. Gehrels and M S. Matthews, Eds. (Univ. of Arizona Press, Tucson, 1984), pp. 150-194; E. Karkoshka and M. G. Tomasko, Icarus 97, 161 (1992)
28. -1 per scale height in the latitude range 0° to 10°N (8), closer to our results.
29. 3 ice particles that presumably form the disturbance clouds.
30. E. J Reese, Icarus 15, 466 (1971).
31. We thank R. Beebe for initiating the HST Director's Discretionary Observation of the 1994 Saturn storm as a service to the community, J. R. Acarreta for the radiative-transfer calculations, and two anonymous reviewers for helpful comments K N was a visiting astronomer at the IRTF, operated by the University of Hawaii under contract from NASA. This work was supported by Universidad Pais Vasco (grant EA054/95) and the French National Programme of Planetology