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Cloud height differences on Saturn
ICARUS 5 2 , 5 0 3 - - 5 0 8
(1982)
Cloud Height Differences on Saturn JEROME APT 1 Planetary Atmospheres Section, Earth and Space Sciences Division, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109
AND R O B E R T B. S I N G E R Planetary Geosciences Hawaii Institute of Geophysics, University of Hawaff, 2525 Correa Road, Honolulu, Hawaii 96822
Received December 7, 1981; revised August 16, 1982 Spectrophotometry from 0.6-2.5 p,m at 1.5% spectral resolution of Saturn's equator and visibly dark South Equatorial Belt near a 1980 ring-plane crossing shows substantially less absorption by methane over the equator than over the SEB. Model fits using Appleby's model atmosphere and a multiple scattering model lead to the conclusion that the pressure levels of the clouds in the two regions differ by 20%. The region of high clouds is coincident with the location of the equatorial fast jet observed by Voyager.
INTRODUCTION
variable filter (CVF) InSb s p e c t r o m e t e r was used on the University of Hawaii 2.2-m On the basis of narrow-band filter pho- telescope with a 1.4-arcsec aperture to retography, Owen (1969) found S a t u r n ' s cord spectra of Saturn and the c o m p a r i s o n equator to be brighter than other regions on stars ot Leonis and 13 G e m on 10 April 1980. the planet in reflected light at the 8900-,~ Spectra were acquired of the N o r t h and methane band. H e suggested that this m a y South polar regions, the equator, and the have been due to a high reflecting layer at South Equatorial Belt [using the definitions the equator. In order to investigate quanti- and notation of R e e s e (1971), we will tatively the varying methane a b u n d a n c e henceforth refer to the SEB]. We present o v e r Saturn's a t m o s p h e r i c regions, we ob- here data for the equator and SEB. For tained photometric reflectance spectra o v e r each region data samples were taken during the range 0.65-2.5 Ixm of selected areas on 20 revolutions of the C V F , each of 20 sec Saturn on 10 April 1980. At this time Sat- duration. The SEB data were acquired beurn's rings subtended only 0.35 arcsec on ginning at 12:31 U T at an equivalent seathe planet, and we were able to o b s e r v e the level airmass of 1.08, while the equatorial regions of interest without substantial con- data run was begun at 12:48 U T at an equivtamination by the rings (Fig. 1). alent sea-level airmass of 1.22. Standard star spectra were recorded before and after OBSERVATIONS the Saturn observations, as well as at other The University of Hawaii Planetary Geo- times for extinction corrections. The data sciences 1.5% spectral resolution circular were ratioed to the solar-type star 16 C Y G B through the intermediate standards listed ~Current address: Code CH6, NASA Johnson above, and are presented in Figs. 2a and b, Space Center, Houston, Texas 77058. and quantitatively in Table I. The error bars 5O3 0019-1035/82/120503-06502.00/0 Copyright © 1982 by Academic Press, Inc. All fights of reproduction in any form reserved.
504
APT AND SINGER N
I/
/I s FIG. 1. The aspect of Saturn as viewed from Earth on 10 April 1980. The circles show the location of our observations with a 1.4-arcsec aperture.
in the figure (_ 1 O'm) include errors in spectra of both Saturn and standards; the signalto-noise is good, even in the deep methane bands (80 : 1 in the 8900-~ band, 200 : 1 in the adjacent continuum). DISCUSSION
Figure 2c is the ratio of the reflected sunlight from the SEB to that of the equator. It is evident that in each of the CH4 absorption bands there is more absorption over the SEB than over the equator. It is also apparent that the atmospheric continuum over the entire wavelength range outside the methane bands is essentially identical over the equator and SEB, although slightly less continuum absorption occurs over the SEB. In order to determine the methane abundance above the two regions we performed model fits using a multiple-scattering model of the type used by Bergstralh et al. (1981), with new methane absorption coefficients supplied by D. C. Benner and U. Fink (private communication). This model uses the Podolak and Danielson (1977) parameterization of stratospheric Axel dust. The Mie scattering parameters used by Podolak and Danielson were converted to equivalent isotropic parameters through the similarity relationships developed by van de Hulst and Grossman (1968). These scattering pa-
rameters were used in a doubling-adding radiative transfer program developed by Martonchik (1975) to calculate a model I/F, with the variable parameter being the methane abundance. In order to compare the data with the I/F generated by the model, we estimated the I/F scale for our observations by convolving the spectra of Bergstralh et al. (1981) with our 1.5% resolution and performing a least-squares fit in the overlap region (0.65-0.82 ~m). Fits for the SEB and equatorial region are shown in Fig. 3. Using the Appleby model (see below), we found that methane abundances over the SEB and equator were 37 and 30 m-agt, respectively. The absolute values of these abundances were uncertain by --+10 m-agt due to model and absorption coefficient uncertainties, but the differential in abundance is better determined: [ C H 4 ] s E B / [ C H 4 ] E Q U = 1.2 -+ 0.1. Using a methane mixing ratio of 7 x l0 -4 and Appleby's model B atmosphere (Appleby, 1980), the equatorial cloud tops would be at 425 mbar and the SEB cloud tops at 530 mbar. According to Appleby's model, these pressures would correspond to equatorial and SEB temperatures of 105° and l l l ° K , respectively. These values would, of course, be altered by a change in the value assumed for the CH4 mixing ratio. A cool equatorial region was reported by
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W A V E L E N G T H IN MICRONS .
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W A V E L E N G T H IN MICRONS i
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W A V E L E N G T H IN M I C R O N S
FIG. 2. (a) Reflectance of S a t u r n ' s South Equatorial Belt (SEB) ratioed to the solar-type star 16 C Y G B. The data have been converted to 1/F by a least-squares fit to that of Bergstralh et al. in the overlap region. The solid line is a spline fit connecting the data points, s h o w n with error bars due to both Saturn and the calibration. The gap near 1.35 p,m is due to the break b e t w e e n the two C V F s used. (b) As in (a), but for the equator. (c) T h e ratio of the SEB/equator, scaled to 1 at 0.83 ~m. The ratio is less than 1 in the m e t h a n e bands, showing substantially greater absorption by CH4 over the SEB than over the equator. 505
506
APT AND SINGER
TABLE I SATURN 1/F Wavelength
SEB
0.680 0.692 0.705 0.716 0.729 0.740 0.752 0.764 0.776 0.786 0.799 0.812 0.822 0.837 0.850 0.862 0.876 0.887 0.900 0.912 0.924 0.936 0.948 0.961 0.973 0.986 0.998 1.011 1.022 1.034 1.047 1.060 1.072 1.085 1.098 1.110 1.123 1.135 1.148 1.160 1.173 1.185 1.198 1.211 1.223 1.236 1.248 1.261 1.274 1.288
0.777 0.777 0.716 0.635 0.441 0.545 0.750 0.760 0.677 0.578 0.530 0.607 0.719 0.720 0.617 0.410 0.322 0.179 0.135 0.379 0.624 0.765 0.757 0.585 0.339 0.200 0.145 0.146 0.232 0.429 0.632 0.738 0.792 0.768 0.640 0.478 0.226 0.073 0.034 0.011 0.014 0.033 0.086 0.231 0.367 0.434 0.546 0.671 0.751 0.777
Equator
Wavelength
SEB
Equator
0.769 0.762 0.718 0.659 0.498 0.586 0.749 0.764 0.695 0.606 0.562 0.631 0.718 0.722 0.634 0.458 0.380 0.236 0.189 0.418 0.632 0.746 0.732 0.593 0.391 0.271 0.220 0.218 0.293 0.464 0.623 0.716 0.761 0.738 0.630 0.515 0.272 0.115 0.061 0.034 0.044 0.069 0.148 0.294 0.428 0.483 0.574 0.671 0.743 0.773
1.300 1.313 1.329 1.353 1.375 1.398 1.420 1.442 1.464 1.486 1.507 1.525 1.549 1.569 1.590 1.612 1.633 i.655 1.677 1.700 1.722 1.744 1.765 1.787 1.808 1.831 1.853 1.876 1.899 1.922 1.945 1.968 1.991 2.012 2.035 2.058 2.081 2.104 2.127 2.150 2.174 2.197 2.242 2.286 2.349 2.455 2.475 2.495 2.516
0.688 0.438 0.406 0.117 0.025 0.012 0.019 0.037 0.107 0.187 0.374 0.557 0.653 0.688 0.729 0.735 0.416 0.073 0.0t6 0.015 0.005 0.006 0.025 0.007 0.026 0.087 0.102 0.184 0.288 0.202 0.191 0.194 0.202 0.160 0.105 0.057 0.021 0.011 0.009 0.016 0.006 0.001 0.007 0.002 0.003 0.012 0.023 0.040 0.047
0.701 0.495 0.451 0.186 0.072 0.041 0.019 0.075 0.168 0.267 0.434 0.590 0.673 0.697 0.740 0.749 0.477 0.130 0.056 0.059 0.018 0.032 0.058 0.024 0.058 0.168 0.194 0.296 0.388 0.296 0.298 0.307 0.341 0.315 0.242 0.173 0.100 0.052 0.047 0.057 0.032 0.018 0.005 0.005 0.006 0.029 0.092 0.149 0.137
SATURN CLOUD HEIGHTS i
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FIG. 3. (a) The data of Fig. 2a for the SEB are compared to the model fit for a methane abundance of 37 m-agt. (b) The data of Fig. 2b are compared with a model fit for a methane abundance of 30 m-agt.
508
APT AND SINGER
Pioneer 11: both the 20- and 45-1~m radiometer channels showed a brightness temperature decrease of - 3 ° K from 12°S latitude to the equator (Ingersoll et al., 1980, Fig. 2). Voyager has confirmed the presence of a cool equator (Hanel et al., 1981), although their measurements are compared with northern latitudes since their flight path and ring geometry precluded systematic coverage of the southern hemisphere. Teifel" (1977) reports equivalent width measurements for the 0.619- and 0.725-1~m methane bands over the equator and South Temperate Belt (STB). He concludes that the STB upper surface is - 1 0 km lower than that of the equatorial belt. West et al. (1981) acquired CCD images of Saturn in 1979 in the 0.619-, 0.725-, and 0.89-1~m CH4 bands and in nearby continuum regions. Although forced to subtract the contribution from the rings near the equator, they found a ratio of 1.5 ÷ - 0.5 0.35 between the SEB and equatorial methane abundances, consistent with our results. The present data, taken without interference from the rings, and the bulk of other observations give confidence in a model of Saturn's tropical region in which the clouds near the equator reside at a pressure level - 1 0 0 mbar ( - 1 0 km) above those in the SEB, while much smaller height differences exist between features such as the SEB and STB. Further spatially resolved observations and more extensive multiple-scattering modeling are required to determine the extent of any height differences between albedo features at temperate latitudes. ACKNOWLEDGMENTS We wish to thank John Appleby, Jay Bergstralh, Glenn Orton, and Roger N. Clark for very helpful discussions, and U. Fink and D. C. Benner for supplying their methane absorption parameters in advance of
publication. Michael J. S. Belton and an anonymous referee provided very useful suggestions. P. B. Owensby assisted with the observations. This work was partially supported by NASA Grant NSG 7323 to the University of Hawaii and NASA Contract NAS 7100 to the Jet Propulsion Laboratory, California Institute of Technology. REFERENCES APPLEBY, J. F. (1980). Atmospheric Structures o f the Giant Planets from Radiative-Convective Equilibrium Models. Doctoral dissertation, Dept. of Earth and Space Science, SUNY at Stony Brook (unpublished). BERGSTRALH, J. T., G. S. ORTON, D. J. DINER, K. H. BAINES, J. S. NEFF, AND M. A. ALLEN (1981). Spatially resolved absolute spectrophotometry of Saturn 3390 to 8080/~. Icarus 46, 27-39. HANEL, R., B. CONRATH, F. M. FLASAR, V. KUNDE, W. MAGUIRE, J. PEARL, J. PIRRAGLIA, R. SAMUELSON, L. HERATH, M. ALLISON, D. CRUIKSHANK, D. GAUTIER, P. GIERASCH, L. HORN, R. KOPPANV, AND C. PONNAMPERUMA(198 !). Infrared observations of the Saturnian system from Voyager 1. Science 212, 192-200. INGERSOLL, A. P., G. S. ORTON, G. MUNCH, G. NEUGEBAUER, AND S. C. CHASE (1980). Pioneer Saturn infrared radiometer: Preliminary results. Science 207, 439-443. MAgTONCHIg, J. V. (1975). Sulphuric Acid Cloud Interpretation o f the Infrared Spectrum o f Venus. Doctoral dissertation, University of Texas at Austin (unpublished). OWEN, T. (1969). The spectra of Jupiter and Saturn in the photographic infrared. Icarus 10, 355-364. PODOLAK, M., AND R. E. DANIELSON (1977). Axel dust on Saturn and Titan. Icarus 30, 479-492. REESE, E. J. (1971). Recent photographic measurements of Saturn. Icarus 15, 466-479. TEIFEL', V. G. (1977). Latitude differences in the structure of Saturn's cloud layer. Astron. Vest. 11, 14-24. [Solar System Res. 11, 10-18]. VAN DE HULST, H. C., AND K. GROSSMAN (1969). Multiple light scattering in planetary atmospheres. In The Atmospheres o f Venus and Mars (J. C. Brandt and M. B. McElroy, Eds.), pp. 35-55. Gordon & Breach, New York. WEST, R. A., M. G. TOMASKO,B. A. SMITH, M. P. WIJESlNGHE, L. R. DOOSE, H. REITSEMA, AND S. LARSON (1981). Methane band images of Saturn. BAAS 13, 723.
(1982)
Cloud Height Differences on Saturn JEROME APT 1 Planetary Atmospheres Section, Earth and Space Sciences Division, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109
AND R O B E R T B. S I N G E R Planetary Geosciences Hawaii Institute of Geophysics, University of Hawaff, 2525 Correa Road, Honolulu, Hawaii 96822
Received December 7, 1981; revised August 16, 1982 Spectrophotometry from 0.6-2.5 p,m at 1.5% spectral resolution of Saturn's equator and visibly dark South Equatorial Belt near a 1980 ring-plane crossing shows substantially less absorption by methane over the equator than over the SEB. Model fits using Appleby's model atmosphere and a multiple scattering model lead to the conclusion that the pressure levels of the clouds in the two regions differ by 20%. The region of high clouds is coincident with the location of the equatorial fast jet observed by Voyager.
INTRODUCTION
variable filter (CVF) InSb s p e c t r o m e t e r was used on the University of Hawaii 2.2-m On the basis of narrow-band filter pho- telescope with a 1.4-arcsec aperture to retography, Owen (1969) found S a t u r n ' s cord spectra of Saturn and the c o m p a r i s o n equator to be brighter than other regions on stars ot Leonis and 13 G e m on 10 April 1980. the planet in reflected light at the 8900-,~ Spectra were acquired of the N o r t h and methane band. H e suggested that this m a y South polar regions, the equator, and the have been due to a high reflecting layer at South Equatorial Belt [using the definitions the equator. In order to investigate quanti- and notation of R e e s e (1971), we will tatively the varying methane a b u n d a n c e henceforth refer to the SEB]. We present o v e r Saturn's a t m o s p h e r i c regions, we ob- here data for the equator and SEB. For tained photometric reflectance spectra o v e r each region data samples were taken during the range 0.65-2.5 Ixm of selected areas on 20 revolutions of the C V F , each of 20 sec Saturn on 10 April 1980. At this time Sat- duration. The SEB data were acquired beurn's rings subtended only 0.35 arcsec on ginning at 12:31 U T at an equivalent seathe planet, and we were able to o b s e r v e the level airmass of 1.08, while the equatorial regions of interest without substantial con- data run was begun at 12:48 U T at an equivtamination by the rings (Fig. 1). alent sea-level airmass of 1.22. Standard star spectra were recorded before and after OBSERVATIONS the Saturn observations, as well as at other The University of Hawaii Planetary Geo- times for extinction corrections. The data sciences 1.5% spectral resolution circular were ratioed to the solar-type star 16 C Y G B through the intermediate standards listed ~Current address: Code CH6, NASA Johnson above, and are presented in Figs. 2a and b, Space Center, Houston, Texas 77058. and quantitatively in Table I. The error bars 5O3 0019-1035/82/120503-06502.00/0 Copyright © 1982 by Academic Press, Inc. All fights of reproduction in any form reserved.
504
APT AND SINGER N
I/
/I s FIG. 1. The aspect of Saturn as viewed from Earth on 10 April 1980. The circles show the location of our observations with a 1.4-arcsec aperture.
in the figure (_ 1 O'm) include errors in spectra of both Saturn and standards; the signalto-noise is good, even in the deep methane bands (80 : 1 in the 8900-~ band, 200 : 1 in the adjacent continuum). DISCUSSION
Figure 2c is the ratio of the reflected sunlight from the SEB to that of the equator. It is evident that in each of the CH4 absorption bands there is more absorption over the SEB than over the equator. It is also apparent that the atmospheric continuum over the entire wavelength range outside the methane bands is essentially identical over the equator and SEB, although slightly less continuum absorption occurs over the SEB. In order to determine the methane abundance above the two regions we performed model fits using a multiple-scattering model of the type used by Bergstralh et al. (1981), with new methane absorption coefficients supplied by D. C. Benner and U. Fink (private communication). This model uses the Podolak and Danielson (1977) parameterization of stratospheric Axel dust. The Mie scattering parameters used by Podolak and Danielson were converted to equivalent isotropic parameters through the similarity relationships developed by van de Hulst and Grossman (1968). These scattering pa-
rameters were used in a doubling-adding radiative transfer program developed by Martonchik (1975) to calculate a model I/F, with the variable parameter being the methane abundance. In order to compare the data with the I/F generated by the model, we estimated the I/F scale for our observations by convolving the spectra of Bergstralh et al. (1981) with our 1.5% resolution and performing a least-squares fit in the overlap region (0.65-0.82 ~m). Fits for the SEB and equatorial region are shown in Fig. 3. Using the Appleby model (see below), we found that methane abundances over the SEB and equator were 37 and 30 m-agt, respectively. The absolute values of these abundances were uncertain by --+10 m-agt due to model and absorption coefficient uncertainties, but the differential in abundance is better determined: [ C H 4 ] s E B / [ C H 4 ] E Q U = 1.2 -+ 0.1. Using a methane mixing ratio of 7 x l0 -4 and Appleby's model B atmosphere (Appleby, 1980), the equatorial cloud tops would be at 425 mbar and the SEB cloud tops at 530 mbar. According to Appleby's model, these pressures would correspond to equatorial and SEB temperatures of 105° and l l l ° K , respectively. These values would, of course, be altered by a change in the value assumed for the CH4 mixing ratio. A cool equatorial region was reported by
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W A V E L E N G T H IN MICRONS .
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W A V E L E N G T H IN MICRONS i
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,,
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.,
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W A V E L E N G T H IN M I C R O N S
FIG. 2. (a) Reflectance of S a t u r n ' s South Equatorial Belt (SEB) ratioed to the solar-type star 16 C Y G B. The data have been converted to 1/F by a least-squares fit to that of Bergstralh et al. in the overlap region. The solid line is a spline fit connecting the data points, s h o w n with error bars due to both Saturn and the calibration. The gap near 1.35 p,m is due to the break b e t w e e n the two C V F s used. (b) As in (a), but for the equator. (c) T h e ratio of the SEB/equator, scaled to 1 at 0.83 ~m. The ratio is less than 1 in the m e t h a n e bands, showing substantially greater absorption by CH4 over the SEB than over the equator. 505
506
APT AND SINGER
TABLE I SATURN 1/F Wavelength
SEB
0.680 0.692 0.705 0.716 0.729 0.740 0.752 0.764 0.776 0.786 0.799 0.812 0.822 0.837 0.850 0.862 0.876 0.887 0.900 0.912 0.924 0.936 0.948 0.961 0.973 0.986 0.998 1.011 1.022 1.034 1.047 1.060 1.072 1.085 1.098 1.110 1.123 1.135 1.148 1.160 1.173 1.185 1.198 1.211 1.223 1.236 1.248 1.261 1.274 1.288
0.777 0.777 0.716 0.635 0.441 0.545 0.750 0.760 0.677 0.578 0.530 0.607 0.719 0.720 0.617 0.410 0.322 0.179 0.135 0.379 0.624 0.765 0.757 0.585 0.339 0.200 0.145 0.146 0.232 0.429 0.632 0.738 0.792 0.768 0.640 0.478 0.226 0.073 0.034 0.011 0.014 0.033 0.086 0.231 0.367 0.434 0.546 0.671 0.751 0.777
Equator
Wavelength
SEB
Equator
0.769 0.762 0.718 0.659 0.498 0.586 0.749 0.764 0.695 0.606 0.562 0.631 0.718 0.722 0.634 0.458 0.380 0.236 0.189 0.418 0.632 0.746 0.732 0.593 0.391 0.271 0.220 0.218 0.293 0.464 0.623 0.716 0.761 0.738 0.630 0.515 0.272 0.115 0.061 0.034 0.044 0.069 0.148 0.294 0.428 0.483 0.574 0.671 0.743 0.773
1.300 1.313 1.329 1.353 1.375 1.398 1.420 1.442 1.464 1.486 1.507 1.525 1.549 1.569 1.590 1.612 1.633 i.655 1.677 1.700 1.722 1.744 1.765 1.787 1.808 1.831 1.853 1.876 1.899 1.922 1.945 1.968 1.991 2.012 2.035 2.058 2.081 2.104 2.127 2.150 2.174 2.197 2.242 2.286 2.349 2.455 2.475 2.495 2.516
0.688 0.438 0.406 0.117 0.025 0.012 0.019 0.037 0.107 0.187 0.374 0.557 0.653 0.688 0.729 0.735 0.416 0.073 0.0t6 0.015 0.005 0.006 0.025 0.007 0.026 0.087 0.102 0.184 0.288 0.202 0.191 0.194 0.202 0.160 0.105 0.057 0.021 0.011 0.009 0.016 0.006 0.001 0.007 0.002 0.003 0.012 0.023 0.040 0.047
0.701 0.495 0.451 0.186 0.072 0.041 0.019 0.075 0.168 0.267 0.434 0.590 0.673 0.697 0.740 0.749 0.477 0.130 0.056 0.059 0.018 0.032 0.058 0.024 0.058 0.168 0.194 0.296 0.388 0.296 0.298 0.307 0.341 0.315 0.242 0.173 0.100 0.052 0.047 0.057 0.032 0.018 0.005 0.005 0.006 0.029 0.092 0.149 0.137
SATURN CLOUD HEIGHTS i
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FIG. 3. (a) The data of Fig. 2a for the SEB are compared to the model fit for a methane abundance of 37 m-agt. (b) The data of Fig. 2b are compared with a model fit for a methane abundance of 30 m-agt.
508
APT AND SINGER
Pioneer 11: both the 20- and 45-1~m radiometer channels showed a brightness temperature decrease of - 3 ° K from 12°S latitude to the equator (Ingersoll et al., 1980, Fig. 2). Voyager has confirmed the presence of a cool equator (Hanel et al., 1981), although their measurements are compared with northern latitudes since their flight path and ring geometry precluded systematic coverage of the southern hemisphere. Teifel" (1977) reports equivalent width measurements for the 0.619- and 0.725-1~m methane bands over the equator and South Temperate Belt (STB). He concludes that the STB upper surface is - 1 0 km lower than that of the equatorial belt. West et al. (1981) acquired CCD images of Saturn in 1979 in the 0.619-, 0.725-, and 0.89-1~m CH4 bands and in nearby continuum regions. Although forced to subtract the contribution from the rings near the equator, they found a ratio of 1.5 ÷ - 0.5 0.35 between the SEB and equatorial methane abundances, consistent with our results. The present data, taken without interference from the rings, and the bulk of other observations give confidence in a model of Saturn's tropical region in which the clouds near the equator reside at a pressure level - 1 0 0 mbar ( - 1 0 km) above those in the SEB, while much smaller height differences exist between features such as the SEB and STB. Further spatially resolved observations and more extensive multiple-scattering modeling are required to determine the extent of any height differences between albedo features at temperate latitudes. ACKNOWLEDGMENTS We wish to thank John Appleby, Jay Bergstralh, Glenn Orton, and Roger N. Clark for very helpful discussions, and U. Fink and D. C. Benner for supplying their methane absorption parameters in advance of
publication. Michael J. S. Belton and an anonymous referee provided very useful suggestions. P. B. Owensby assisted with the observations. This work was partially supported by NASA Grant NSG 7323 to the University of Hawaii and NASA Contract NAS 7100 to the Jet Propulsion Laboratory, California Institute of Technology. REFERENCES APPLEBY, J. F. (1980). Atmospheric Structures o f the Giant Planets from Radiative-Convective Equilibrium Models. Doctoral dissertation, Dept. of Earth and Space Science, SUNY at Stony Brook (unpublished). BERGSTRALH, J. T., G. S. ORTON, D. J. DINER, K. H. BAINES, J. S. NEFF, AND M. A. ALLEN (1981). Spatially resolved absolute spectrophotometry of Saturn 3390 to 8080/~. Icarus 46, 27-39. HANEL, R., B. CONRATH, F. M. FLASAR, V. KUNDE, W. MAGUIRE, J. PEARL, J. PIRRAGLIA, R. SAMUELSON, L. HERATH, M. ALLISON, D. CRUIKSHANK, D. GAUTIER, P. GIERASCH, L. HORN, R. KOPPANV, AND C. PONNAMPERUMA(198 !). Infrared observations of the Saturnian system from Voyager 1. Science 212, 192-200. INGERSOLL, A. P., G. S. ORTON, G. MUNCH, G. NEUGEBAUER, AND S. C. CHASE (1980). Pioneer Saturn infrared radiometer: Preliminary results. Science 207, 439-443. MAgTONCHIg, J. V. (1975). Sulphuric Acid Cloud Interpretation o f the Infrared Spectrum o f Venus. Doctoral dissertation, University of Texas at Austin (unpublished). OWEN, T. (1969). The spectra of Jupiter and Saturn in the photographic infrared. Icarus 10, 355-364. PODOLAK, M., AND R. E. DANIELSON (1977). Axel dust on Saturn and Titan. Icarus 30, 479-492. REESE, E. J. (1971). Recent photographic measurements of Saturn. Icarus 15, 466-479. TEIFEL', V. G. (1977). Latitude differences in the structure of Saturn's cloud layer. Astron. Vest. 11, 14-24. [Solar System Res. 11, 10-18]. VAN DE HULST, H. C., AND K. GROSSMAN (1969). Multiple light scattering in planetary atmospheres. In The Atmospheres o f Venus and Mars (J. C. Brandt and M. B. McElroy, Eds.), pp. 35-55. Gordon & Breach, New York. WEST, R. A., M. G. TOMASKO,B. A. SMITH, M. P. WIJESlNGHE, L. R. DOOSE, H. REITSEMA, AND S. LARSON (1981). Methane band images of Saturn. BAAS 13, 723.