Vertical cloud distribution in the Uranian atmosphere
In this work, the vertical cloud distribution in the Uranian atmosphere is investigated. We used the method of determinination of the deviation scope of the real atmosphere from homogeneity conditions. The idea of this methods is that the diffusely reffected radiations form at different effective de...
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irk-123456789-1190862017-06-04T03:03:10Z Vertical cloud distribution in the Uranian atmosphere Kostogryz, N.M. In this work, the vertical cloud distribution in the Uranian atmosphere is investigated. We used the method of determinination of the deviation scope of the real atmosphere from homogeneity conditions. The idea of this methods is that the diffusely reffected radiations form at different effective depths in the atmosphere, namely: the strong absorption bands form higher in the atmosphere than weak ones. The same is for separate absorption bands: their centres form in higher atmospheric layers than other points of bands or lines contours. The relative methane concentration for all points of the contours of absorption bands will be the same only for a homogeneous atmosphere and will show the systematic deviation in the center and near the edge of the absorption bands in the case of an inhomogeneous atmosphere. It was obtained that Uranus' atmosphere has two cloud layers: the first one in the region with pressure within the range 1.5 − 1.8 bar, and the second one in the region with the pressure 3.5 − 5.5 bar. We also can conclude that aerosol was more abundant in 1981 compared to 1993 and 1995 which was found in our previous work. 2011 Article Vertical cloud distribution in the Uranian atmosphere / N.M. Kostogryz // Advances in Astronomy and Space Physics. — 2011. — Т. 1., вип. 1-2. — С. 77-80. — Бібліогр.: 22 назв. — англ. 987-966-439-367-3 http://dspace.nbuv.gov.ua/handle/123456789/119086 en Advances in Astronomy and Space Physics Advances in astronomy and space physics |
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In this work, the vertical cloud distribution in the Uranian atmosphere is investigated. We used the method of determinination of the deviation scope of the real atmosphere from homogeneity conditions. The idea of this methods is that the diffusely reffected radiations form at different effective depths in the atmosphere, namely: the strong absorption bands form higher in the atmosphere than weak ones. The same is for separate absorption bands: their centres form in higher atmospheric layers than other points of bands or lines contours. The relative methane concentration for all points of the contours of absorption bands will be the same only for a homogeneous atmosphere and will show the systematic deviation in the center and near the edge of the absorption bands in the case of an inhomogeneous atmosphere. It was obtained that Uranus' atmosphere has two cloud layers: the first one in the region with pressure within the range 1.5 − 1.8 bar, and the second one in the region with the pressure 3.5 − 5.5 bar. We also can conclude that
aerosol was more abundant in 1981 compared to 1993 and 1995 which was found in our previous work. |
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Kostogryz, N.M. |
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Kostogryz, N.M. Vertical cloud distribution in the Uranian atmosphere Advances in Astronomy and Space Physics |
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Kostogryz, N.M. |
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Kostogryz, N.M. |
| title |
Vertical cloud distribution in the Uranian atmosphere |
| title_short |
Vertical cloud distribution in the Uranian atmosphere |
| title_full |
Vertical cloud distribution in the Uranian atmosphere |
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Vertical cloud distribution in the Uranian atmosphere |
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Vertical cloud distribution in the Uranian atmosphere |
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vertical cloud distribution in the uranian atmosphere |
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Advances in astronomy and space physics |
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2011 |
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http://dspace.nbuv.gov.ua/handle/123456789/119086 |
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Vertical cloud distribution in the Uranian atmosphere / N.M. Kostogryz // Advances in Astronomy and Space Physics. — 2011. — Т. 1., вип. 1-2. — С. 77-80. — Бібліогр.: 22 назв. — англ. |
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Advances in Astronomy and Space Physics |
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AT kostogryznm verticalclouddistributionintheuranianatmosphere |
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2025-07-08T15:12:12Z |
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2025-07-08T15:12:12Z |
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Vertical cloud distribution in the Uranian atmosphere
N. M. Kostogryz
Main Astronomical Observatory of NAS of Ukraine, Zabolotnoho st., 27, 03680, Kyiv, Ukraine
kosn@mao.kiev.ua
In this work, the vertical cloud distribution in the Uranian atmosphere is investigated. We used the
method of determinination of the deviation scope of the real atmosphere from homogeneity conditions.
The idea of this methods is that the di�usely re�ected radiations form at di�erent e�ective depths in the
atmosphere, namely: the strong absorption bands form higher in the atmosphere than weak ones. The same
is for separate absorption bands: their centres form in higher atmospheric layers than other points of bands
or lines contours. The relative methane concentration for all points of the contours of absorption bands
will be the same only for a homogeneous atmosphere and will show the systematic deviation in the center
and near the edge of the absorption bands in the case of an inhomogeneous atmosphere. It was obtained
that Uranus' atmosphere has two cloud layers: the �rst one in the region with pressure within the range
1.5 − 1.8 bar, and the second one in the region with the pressure 3.5 − 5.5 bar. We also can conclude that
aerosol was more abundant in 1981 compared to 1993 and 1995 which was found in our previous work.
Introduction
Visible and near infrared spectrum of Uranus is formed by the re�ection of the sunlight from clouds and
hazes, modulated mainly by the absorption of atmospheric methane. This spectral region is highly useful
for determining the vertical cloud structure, since in the region of strong methane absorption only re�ection
from upper level hazes are observed, while in the regions of low absorption re�ection from cloud layers down
to 10 bars may be observed.
The vertical structure of Uranus has been the source of big debate. The Voyager 2 radio-occultation ex-
periments [13] detected the presence of a thin cloud layer at 1.5 bars, assumed to be methane ice. Baines et al.
[1] also deduced the presence of a thin cloud layer near 1.5 bars level, together with a second thicker cloud
layer near 3 bars. Rages et al. [19] used Voyager 2 data and incorporated cloud physics calculations for the
haze in the upper atmosphere. Methane was expected to form a cloud near 1.4 bars, and the Voyager occul-
tation data [13] showed indication of a methane cloud. This approach produced models with one higher layer
and two cloud layers below at the methane condensation level and near 3 bars. This model was modi�ed by
the inclusion of high resolution spectroscopy [2], Keck imaging [20], and near-infrared spectroscopy [6, 21].
The present work focuses on the vertical cloud distribution based on the data of Uranian geometric albedo
[7, 8, 18] in the methane bands 887 nm, 727 nm, 619 nm, 543 nm using a technique of vertical structure
deviations from the homogeneity conditions [14].
The method of calculations
The uncertainty of the atmospheric model choice during the analysis of spectral data of geometric albedo
made us to �nd the technique which qualitatively demonstrates the deviation scope of the real atmosphere
from the homogeneity. Such technique was proposed by Morozhenko [14]. The idea of this technique lies in
the decreasing of probability of light quantum penetrations in the deep atmospheric layers depending on the
single scattering albedo decreasing. It means, that the di�usely re�ected radiation originates from di�erent
e�ective depths in the atmosphere, namely: the strong absorption bands form higher in the atmosphere than
weak ones. The same is for separate absorption bands: their centers form at higher atmospheric layers than
other points of bands or lines contours. The relative methane concentration for all points of the contours of
absorption bands will be the same only for a homogeneous atmosphere and will show the systematic deviation
in the center and near edge of the absorption bands in the case of an inhomogeneous atmosphere.
As model values of geometric albedo we used those calculated by Ovsak (private communication, part
of calculations published in [15], p. 206) for a plane parallel, homogeneous semi-in�nite layer illuminated
by a parallel rays, with a three parameter Henyey-Greenstein phase function (g1 = 0.25, g2 = −0.25, a =
77
Advances in Astronomy and Space Physics N. M. Kostogryz
0.5 (x1 = 0)), where x1 is the �rst coe�cient of phase function series expansion in Legendre polynomials.
We adopted that the atmosphere of Uranus is a homogeneous semi-in�nite gas-aerosol layer. Comparing
observed and calculated data on geometric albedo, we obtained ln[ τν+τκ
τS
], ln τS and ln τν . Here ln τν , ln τκ
are the absorption optical depth in the absorption bands and continuum, correspondingly, and ln τS is the
total (gas+aerosol) scattering optical depth.
The amount of methane NL along the line of sight is calculated using the following formula:
lnNL = ln τν − ln kν . (1)
The values of methane absorption coe�cients kν were taken from [4] and rede�ned by [16] with regard for
temperature-pressure dependence.
On Jupiter and Saturn, methane is expected to be uniformly mixed throughout the troposphere at all
latitudes. Thus, the distribution of aerosol opacity can be directly inferred from methane band imaging. On
Uranus, the methane mixing ratio in the upper troposphere varies vertically by three orders of magnitude.
Unlike Jupiter and Saturn, The relative methane concentration changes from the upper to the deeper layers
in the Uranian atmosphere. Thus, τR is determined in the following way:
ln τR = D lnNL− ln γ0 − ln τR0 . (2)
Here D < 1, γ0 is the relative methane concentration at the atmospheric layer with lnNL = 0, ln τR0 is the
value of ln τR for hydrogen-helium mixture which extends up to 1 km-amagat at the 887 nm wavelength.
The atmospheric pressure is calculated with the following formula:
ln p = ln A + ln τR, (3)
where A corresponds to the mean of pressure where τR(887.2 nm) = 1.
In this work we used the following expression for depth dependence of the relative methane concentration
proposed in [17]:
{
ln γ(p) = −9.98 + 2.68∆ ln p in the range 0.36 ≤ ln p ≤ 1.55,
γ = 0.00382 in the range ln p > 1.62.
In this case, expression (2) will look like:
{
ln τR = −1.73 + 0.27 ln NL in the range −4.92 ≤ ln NL ≤ −0.6,
τR = 0.15 + ∆NL/12.86 in the range NL ≥ 0.55.
Results and conclusions
Using the technique of estimating the deviation scope of real atmosphere from the homogeneity, we can
identify two cloud layers: the �rst one near 1.5− 1.8 bars (Fig. 2) and the second one near ∼ 3.5− 5.5 bars
(Fig. 1). In Figure 1 a) the homogeneity conditions, i.e. clear gaseous atmosphere, are presented, while in
Figure 1 b), c), d) the deviation scope from the homogeneity for di�erent years of observations, i.e. real
gas+aerosol atmosphere, are shown. In Figure 1 b),c),d) the scattering optical depths for 887 nm are very
close to those for 727 nm, therefore we moved 887 nm band down to 0.5 values for better understanding.
As it can be seen from the Fig. 1, the real atmosphere is quite di�erent from clear gaseous atmosphere,
especially in the pressure region ∼ 3.5− 5.5 bars. It means, that in this pressure region Uranus has a strong
aerosol layer.
This result is in a good agreement with [20], where the presence of the second cloud layer at 4 − 5 bars
was detected, while in the other papers [5, 6, 22, 21] the presence of the second cloud layer some deeper in
the atmosphere, from 6− 8 bars to 8− 10 bars, is discussed.
Figure 1 also shows the aerosol abundance in the atmosphere. As in the gaseous atmosphere (Fig. 1,a)
the considerable di�erences are visible between red and blue wings of methane band, in the real atmosphere
these di�erences are noticeably less. So, the less di�erences between red and blue wings are visible, the more
aerosol abundance present in the atmosphere. We can conclude that in 1981 the aerosol was more abundant,
than in 1993 and 1995. This result was obtained in our previous papers [11, 12] using quite di�erent technique
for aerosol abundance calculation.
78
Advances in Astronomy and Space Physics N. M. Kostogryz
Figure 1: Logarithmic pressure dependence of the scattering optical depth: a) model of clear gaseous atmosphere,
b) model of gas+aerosol atmosphere in 1981, c) model of gas+aerosol atmosphere in 1993, d) model of gas+aerosol
atmosphere in 1995. In b), c), d) left vertical scale is for 543 nm, 619 nm, 727 nm, and right vertical scale is for
887 nm.
Upper cloud layer can be identi�ed from Figure 2, which presents the logarithmic dependence of scattering
optical depth from pressure for 887 nm methane band in 1981, 1993 and 1995. Fig. 3 shows minimum and
maximum limits of errors for 1981. As one can see from Fig. 2 and 3, the upper cloud layer lies in the pressure
region ∼ 1.5−1.8 bars, and is much thinner than deeper layer. Because of the lack of near-infrared geometric
albedo data, we have no possibility to conclude about upper limit of this layer, but we can conclude that at
1.5 bar this layer is present.
As the upper thin cloud layer assumed to be methane ice, and methane was expected to form a cloud near
1.4 bar, we obtained a very good agreement with this assumption. This result was con�rmed by Voyager 2
radio occultation experiment [13] that detected the presence of a thin cloud layer at 1.5 bar and Rages et
al. [19] who talked about methane cloud layer occupying 1.2-1.3 bars at 22.5◦ S, rising to 2.4 bar at 65◦ S
and Karkoschka and Tomasko [9], who con�rmed that Uranus has very small aerosol opacity above the
1.2 bar level, but much larger opacity below. But, in the same time, this result has some disagreements with
[6, 22, 21]. These disagreements could be resolved by adjusting methane coe�cients. Using new methane
absorption coe�cients from [10], Fry and Sromovsky [3] �tted Uranus near-IR spectra previously analyzed
in [22, 21] using methane absorption coe�cients from [5]. Because the new absorption coe�cients usually
result in higher opacities at the low temperatures seen in Uranus' upper troposphere, previously derived
cloud altitudes were expected to generally rise to higher altitudes [3] and pressure of the upper tropospheric
cloud to decrease to 1.6 bars (from 2.4 bars using Irwin coe�cients [5]).
From our results we can conclude, that Uranus' atmosphere has two cloud layers: the �rst one is in region
with the pressure from 1.5 bar to 1.8 bar, and the second one is the region with the pressure from 3.5 bar to
5.5 bar.
Acknowledgement
I would like to thank O. Morozhenko for the critical discussions on this work.
79
Advances in Astronomy and Space Physics N. M. Kostogryz
Figure 2: Logarithmic pressure dependence of sca-
tering optical depth for 887 nm methane band in
di�erent years.
0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
0,5
ln
S
lnp
ln
S
(lnp)
ln
Smin
(lnp)
ln
Smax
(lnp)
ln
R
(lnp)
Uranus, 1981, 887nm
Figure 3: Logarithmic pressure dependence of sca-
tering optical depth for 887 nm methane band in
1981 with upper and lower limits of errors
References
[1] Baines K. H., Bergstralh J. T. Icarus, V. 65, pp. 406-441 (1986)
[2] Baines K. H., Mickelson M. E., Larson L. E. et al. Icarus, V. 114, pp. 328-340 (1995)
[3] Fry P. M., Sromovsky L. A. DPS meeting, 41 (2009)
[4] Giver L. P., J. Quant. Spectrosc. and Radiat. Transfer, V. 19, pp. 311-322 (1978)
[5] Irwin P. G. J., Sromovsky L. A., Strong E. K. et al. Icarus, V. 181, pp. 309-319 (2006)
[6] Irwin P. G. J., Teanby N. A., Davis G. R. Astrophys. J., V. 665, pp. L71-L74 (2007)
[7] Karkoschka E. Icarus, V. 111, pp. 174-192 (1994)
[8] Karkoschka E. Icarus, V. 133, pp. 134-146 (1998)
[9] Karkoschka E., Tomasko M. Icarus, V. 202, pp. 287-309 (2009)
[10] Karkoschka E., Tomasko M. Icarus, V. 205, pp. 674-694 (2010)
[11] Kostogryz N. M. Kinematics and Physics of Celestial Bodies, V. 23, pp. 214-220 (2007)
[12] Kostogryz N. M. YSC'14 Proc. of Contributed Papers, eds.: Ivashchenko G., Golovin A., Kyivskyi Universytet, Kyiv,
pp. 44-48 (2007)
[13] Lindal G. F., Lyons J. R., Sweetnam D. N. J. Geophys. Res., V. 92, pp. 14987-15001 (1987)
[14] Morozhenko A. V. Soviet Astr. Lett. (TR:PISMA) V. 10, pp. 323 (1984)
[15] Morozhenko A.V. Techniques and results of remote sensing of planetary atmospheres. Kyiv, Naukova dumka press (2004)
[16] Morozhenko A. V. Kinematika i Fizika Nebesnykh Tel, V. 22, pp. 138-153 (2006)
[17] Morozhenko A. V. Ovsak A. S. Kinematics and Physics of Celestial Bodies, V. 25, pp. 173-181(2009)
[18] Ne� J. S., Humm D. C., Bergstralh J. T. et al. Icarus, V .60, pp. 221-235 (1984)
[19] Rages K., Pollack J. B., Tomasko M. G. et al. Icarus, V. 89, pp. 359-376 (1991)
[20] Sromovsky L. A., Fry P. M. Icarus, V. 192, pp. 527-557 (2007)
[21] Sromovsky L. A., Fry P. M. Icarus, V. 193, pp. 252-266 (2008)
[22] Sromovsky L. A., Irwin P. G. J., Fry P. M. Icarus, V. 182, pp. 577-593 (2006)
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