On a mechanism of polarization origin at the polar regions of Jupiter
We propose the following mechanism of linear polarization origin at Jupiter’s polar regions: the principal contribution in polarization is made by the light reflected by cloud layer and then scattered by stratospheric aerosol particles. The linear polarization distributions along the central meridia...
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| Cite this: | On a mechanism of polarization origin at the polar regions of Jupiter / O.S. Goryunova, V.V. Korokhin, L.A. Akimov, E.V. Shalygin, Yu.I. Velikodsky // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 443-447. — Бібліогр.: 16 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859850844280717312 |
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| author | Goryunova, O.S. Korokhin, V.V. Akimov, L.A. Shalygin, E.V. Velikodsky, Yu.I. |
| author_facet | Goryunova, O.S. Korokhin, V.V. Akimov, L.A. Shalygin, E.V. Velikodsky, Yu.I. |
| citation_txt | On a mechanism of polarization origin at the polar regions of Jupiter / O.S. Goryunova, V.V. Korokhin, L.A. Akimov, E.V. Shalygin, Yu.I. Velikodsky // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 443-447. — Бібліогр.: 16 назв. — англ. |
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| description | We propose the following mechanism of linear polarization origin at Jupiter’s polar regions: the principal contribution in polarization is made by the light reflected by cloud layer and then scattered by stratospheric aerosol particles. The linear polarization distributions along the central meridian for two spectral bands (0.46 μm and 0.70 μm) are calculated. They are in good qualitative agreement with observational data. The mean scattering particle radius is estimated as rmean = 0.5 μm.
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| first_indexed | 2025-12-07T15:41:10Z |
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ON A MECHANISM OF POLARIZATION ORIGIN
AT THE POLAR REGIONS OF JUPITER
O. S. Goryunova, V. V. Korokhin, L. A. Akimov,
E. V. Shalygin, Yu. I. Velikodsky
Institute of Astronomy, V.N.Karazin Kharkiv National University
35 Sumska Str., 61022 Kharkiv, Ukraine
e-mail: dslpp@astron.kharkov.ua
We propose the following mechanism of linear polarization origin at Jupiter’s polar regions:
the principal contribution in polarization is made by the light reflected by cloud layer and then
scattered by stratospheric aerosol particles. The linear polarization distributions along the central
meridian for two spectral bands (0.46 μm and 0.70 μm) are calculated. They are in good qual-
itative agreement with observational data. The mean scattering particle radius is estimated as
rmean = 0.5 μm.
INTRODUCTION
At present, the following observational facts are well-known.
1. Ground-based polarimetrical observations of Jupiter in the visual portion of spectrum show linear polari-
zation degree P dependence on phase angle α. For the central region of Jupiter disc, the polarization
changes from zero value at the phase angle α = 0◦ to several fractions of percent at α = 11◦ [9].
2. Observations show that P increases with latitude even at the zero phase angle for Jupiter [11–13].
At the polar regions (latitudes are more than 45◦– 50◦), P reaches 7–8% for the blue region of spec-
trum (Fig. 1) [11–13].
3. There is a strong P dependence on wavelength at the polar regions (with change of P sign and crossing
the zero value at λ = 0.75 μm) [12].
4. At the Kharkiv Astronomical Observatory, in 1981, Starodubtseva and Akimov started regular polarimet-
ric observations of Jupiter near opposition. Based on more than 20-year observations, the North–South
asymmetry of P and its seasonal and longitudinal variations were found [11]. Let us name asymmetry
a difference between values of P in the North and the South at the latitudes ±60◦ on the central meridian.
-90 -60 -30 0 30 60 90
Latitude, degrees
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
P
,%
bFigure 1. Typical distribution of P along the central meridian of Jupiter near opposition (λeff = 0.46 μm)
For explanation of the observational facts, various models were developed, for example, Morozhenko’s and
Yanovitskij’s models of Jupiter’s atmosphere [9], Dlugach’s and Mishchenko’s model [2]. For interpretation
of space data, Smith and Tomasko [10] proposed and Braak et al. [1] used the four-layer model of Jupiter’s
atmosphere.
It should be noted that all presented models were developed and used for interpretation of observations of
the central regions of Jupiter. They do not provide an explanation of P behaviour at the polar regions and,
especially, do not give any mechanism of polarization origin at the zero phase angle of Jupiter.
Therefore, we start developing such a model to apply it for interpretation of our observations.
c© O. S. Goryunova, V. V. Korokhin, L. A. Akimov, E. V. Shalygin, Yu. I. Velikodsky, 2004
443
OUR PHYSICAL MECHANISM OF POLARIZATION ORIGIN AT THE POLAR REGIONS
It is known that polarization at the polar regions of Jupiter is caused by scattering in upper layers of the at-
mosphere. We suppose that the principal part of polarized light at zero phase angle is the radiation reflected
from the planet surface, i.e., underlaying surface (clouds) and then scattered by stratospheric aerosols.
Data of observations and simulations at other wavelengths (especially, at UV and blue spectral regions)
show that there is a stratospheric haze at altitudes with a pressure about a few tenths of mbar with much more
abundance at the polar regions [6, 10, 14]. It is very likely that aerosol in haze is unstable and sensitive to
changes of physical conditions which can influence aerosol formation or destruction and thus radiation scattering
processes. It is a qualitative explanation of seasonal (caused by changing the atmosphere insolation) and
longitudinal (caused by influence of the Jovian magnetic field on charged particles falling on stratosphere)
variations of North–South asymmetry of P .
The light I which is detected by an observer consists of three parts: I = Ic + Ich + Ih, where Ic is the light
reflected by planet surface (clouds); Ich is the light reflected by the surface and then scattered by aerosols (beam
is shown in Fig. 2); Ih denotes the light scattered only by aerosol haze.
Figure 2. General model scheme
According to estimated data from [4], particle concentration in aerosol haze is relatively small (1–10 cm−3),
therefore the most part of radiation Ic probably will freely pass to observer and will make the principal contribu-
tion to the summary intensity. If we consider that the surface radiates unpolarized light, then the Ic-component
contribution to the polarization must be taken into account as depolarization. Factual data on small particle
concentration allow us to suppose that just single scattering makes the main contribution to polarization.
Ih-component makes an insignificant contribution to polarization at the zero phase angle of the planet and
as a first approximation it may be ignored.
Thus, the mechanism of polarization origin at the polar regions of Jupiter lies in scattering of light, which
was reflected by underlaying surface, by aerosol haze. It is clear that radiation comes to the haze area from
the surface part, limited by horizon line (cone in Fig. 2). Therefore, the characteristic scattering angles differ
greatly from zero value.
Proposed scenario was realized in the analytic-computer model as a component in IRIS program complex
environment [7].
MODEL DESCRIPTION
Computer model was developed with the following assumptions:
1. Phase angle of Jupiter equals zero.
2. Jupiter is a sphere. There is a homogeneous thin layer of aerosol haze at the altitude h above surface
(Fig. 2).
3. The aerosol haze consists of spherical unabsorbing particles. To describe light scattering, the Mie theory
is used.
4. The size distribution is the normal one with two parameters: the mean size of particles rmean and standard
deviation σ2
r .
5. Only single scattering (by haze particles) is taken into account.
6. The underlaying surface (clouds) reflects light by Lambert’s law.
444
We separate symbolically input parameters into two groups: physical and geometrical. Physical parameters
are: refractive index of haze particles m; the size distribution parameters; effective wavelength of light λ.
Geometrical parameters are: haze altitude h (see in Fig. 2); planetocentric coordinates of the Sun and observer.
The results of calculations are P distributions over Jupiter’s disc for specified regions.
RESULTS OF COMPUTER SIMULATION
Figure 3 gives the results of the simulation (bold lines). The following input parameters were used for the cal-
culations: Re(m) = 1.5; Im(m) = 0.0; h = 300 km; rmean = 0.5 μm; σr = 0.01 μm. Values of the input
parameters are difficult to choose, therefore, we made an additional research, results of which are presented in
the next item of the paper.
-90 -60 -30 0 30 60 90
Latitude, degrees
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
P,
%
Filter"R"
Calculated curve,
wavelength 0.65 mkm
From observations,
wavelength 0.7mkm
-90 -60 -30 0 30 60 90
Latitude, degrees
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
P,
%
Filter "B"
Calculated curve,
wavelength 0.456 mkm
From observations,
wavelength 0.456 mkm
a b
Figure 3. Dependence of linear polarization degree P on latitude along the central meridian for (a) blue light and (b) red
light
Figure 3 shows the results of comparison of the calculation data (bold lines) with observational data
(thin lines). These observations were carried out by Korokhin and Starodubtseva on September 10, 1998
at the Chuguev Observational Station with the telescope AZT-8.
As seen from the plots, the model and observed curves are in good qualitative agreement.
It should be noted that the increase of polarization with latitude at the blue light begins earlier than at
the red light, which corresponds to the observational data as well.
MODEL ANALYSIS
Figure 4a shows some results of haze altitude h varying. Selecting the value h = 300 km, we followed results
from [8]. However, in [4] the value h = 150–200 km is proposed.
Figure 4a illustrates that value of P increases with haze altitude. Although the curve for h = 1200 km has
better argument with observations, we selected value h = 300 km (bold line), since there are not any rational
arguments for choice of greater values.
We chose benzene as an aerosol material. In [4, 8, 16], probable microphysical and chemical schemes of
polyaromatic hydrocarbons and benzene production at Jupiter’s atmosphere are proposed. For the first time
benzene at Jupiter’s atmosphere was detected in 1985 using the Voyager’s IRIS (Infrared Interferometer Spectro-
meter) at the North region near a latitude of 60◦ [5]. Later, the Complex IR Spectrometer aboard the Cassini
spacecraft observed benzene at North and South high Jupiter’s latitudes [3].
Known refractive index of benzene in standard conditions is m = 1.5 − 0.0i. So, this value was selected for
further calculations.
However, it should be keeping in mind that the Mie theory is sensitive to refractive index m changing.
As Figure 4b shows, even small changing the real part of m results in very dramatic changes of P value.
Therefore, the question of refractive index choosing for Jupiter aerosol haze is still an open one.
In the Mie theory, scattering depends heavily on relative radius of particles, so-called “size parameter” (ratio
of particle size to wavelength).
Figure 5a demonstrates a strong P dependence on wavelength (with sign changing), which corresponds
qualitatively to observations.
445
-90 -60 -30 0 30 60 90
Latitude, degrees
-5
-4
-3
-2
-1
0
1
P
,%
H aze altitude h
�=0.456 �m , rmean=0.5 �m , R e(m )=1.5
h = 150 km
h = 300 km
h = 1200 km
-90 -60 -30 0 30 60 90
Latitude, degrees
-3
-2
-1
0
1
2
P
,%
Ref ractive index m
h=300 km, �=0.456 �m, rmean=0.5 �m
Re(m) = 1.3, Im (m) = 0
Re(m) = 1.5, Im (m) = 0
Re(m) = 1.7, Im (m) = 0
à b
Figure 4. Dependence of linear polarization degree P on latitude along the central meridian for (a) different aerosol
haze altitudes and (b) different refractive indexes
-90 -60 -30 0 30 60 90
Latitude, degrees
-3
-2
-1
0
1
2
3
4
P
,%
W avelength �
h=300 km, rmean=0.5 �m, Re(m)=1.5
0.456 mkm
0.65 mkm
1 mkm
2 mkm
-90 -60 -30 0 30 60 90
Latitude, degrees
-3
-2
-1
0
1
2
3
4
5
P
,%
Mean particles radius rmean
h=300 km, �=0.456 �m, Re(m)=1.5
0.1 mkm
0.2 mkm
0.4 mkm
0.5 mkm
a b
-90 -60 -30 0 30 60 90
Latitude, degrees
-3
-2
-1
0
1
P
,%
S ta n d a r d d e v ia t io n � r
h = 3 0 0 k m , r
m e a n
= 0 .5 �m ,
�= 0 .4 5 6 � m , R e (m )= 1 .5
0 .0 0 1 m k m
0 .0 0 5 m k m
0 .0 1 m k m
0 .1 m k m
c
Figure 5. Dependence of linear polarization degree P on latitude along the central meridian for (a) different wavelengths,
(b) different mean sizes of particles, (c) different standard deviations of particle sizes
446
The mean radius of particles rmean = 0.5 μm is selected as the main value (Fig. 5b) because for this value
there is a change of polarization sign analogously to observations. This value is rather different from proposed
in [12] rmean = 1.0÷ 1.5 μm but it should be noted that in [12] other refractive index values, m = 1.33 and
m = 1.44, are used.
We analysed behaviour of P on varying standard deviation of particle sizes (Fig. 5c). One can see that, with
dispersion increase, curves are ”smoothing”. Because of limitation of computational resources, the main value
σr = 0.01 μm was selected for further investigation. Unfortunately, such a small value of σr causes periodical
“oscillations” of calculated profiles at low latitudes.
CONCLUSIONS
1. A mechanism of polarization origin at Jupiter’s polar regions is proposed.
2. The linear polarization distribution along the central meridian for two spectral bands (0.46 and 0.70 μm)
is calculated.
3. The calculations are in good qualitative agreement with observations.
4. The dependence of polarization on model input parameters is analysed.
5. Calculated P (λ) dependence passes zero at near IR, which is in good agreement with observations.
6. We estimated the mean scattering particle radius rmean = 0.5 μm, which does not contradict other
researchers’ results.
In future, the following evolution of the model presented are planned: adding the possibility to use various
reflective laws; taking into account the haze absorption; adding the mechanisms which will produce the North–
South asymmetry of P and taking into account latitudinal and longitudinal irregularity of haze distribution.
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according earth-based spectropolarimetric observations // Abstracts of NATO ASI, 2003.
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|
| id | nasplib_isofts_kiev_ua-123456789-79696 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 0233-7665 |
| language | English |
| last_indexed | 2025-12-07T15:41:10Z |
| publishDate | 2005 |
| publisher | Головна астрономічна обсерваторія НАН України |
| record_format | dspace |
| spelling | Goryunova, O.S. Korokhin, V.V. Akimov, L.A. Shalygin, E.V. Velikodsky, Yu.I. 2015-04-03T19:34:48Z 2015-04-03T19:34:48Z 2005 On a mechanism of polarization origin at the polar regions of Jupiter / O.S. Goryunova, V.V. Korokhin, L.A. Akimov, E.V. Shalygin, Yu.I. Velikodsky // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 443-447. — Бібліогр.: 16 назв. — англ. 0233-7665 https://nasplib.isofts.kiev.ua/handle/123456789/79696 We propose the following mechanism of linear polarization origin at Jupiter’s polar regions: the principal contribution in polarization is made by the light reflected by cloud layer and then scattered by stratospheric aerosol particles. The linear polarization distributions along the central meridian for two spectral bands (0.46 μm and 0.70 μm) are calculated. They are in good qualitative agreement with observational data. The mean scattering particle radius is estimated as rmean = 0.5 μm. en Головна астрономічна обсерваторія НАН України Кинематика и физика небесных тел MS5: Dynamics and Physics of Solar System Bodies On a mechanism of polarization origin at the polar regions of Jupiter Article published earlier |
| spellingShingle | On a mechanism of polarization origin at the polar regions of Jupiter Goryunova, O.S. Korokhin, V.V. Akimov, L.A. Shalygin, E.V. Velikodsky, Yu.I. MS5: Dynamics and Physics of Solar System Bodies |
| title | On a mechanism of polarization origin at the polar regions of Jupiter |
| title_full | On a mechanism of polarization origin at the polar regions of Jupiter |
| title_fullStr | On a mechanism of polarization origin at the polar regions of Jupiter |
| title_full_unstemmed | On a mechanism of polarization origin at the polar regions of Jupiter |
| title_short | On a mechanism of polarization origin at the polar regions of Jupiter |
| title_sort | on a mechanism of polarization origin at the polar regions of jupiter |
| topic | MS5: Dynamics and Physics of Solar System Bodies |
| topic_facet | MS5: Dynamics and Physics of Solar System Bodies |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/79696 |
| work_keys_str_mv | AT goryunovaos onamechanismofpolarizationoriginatthepolarregionsofjupiter AT korokhinvv onamechanismofpolarizationoriginatthepolarregionsofjupiter AT akimovla onamechanismofpolarizationoriginatthepolarregionsofjupiter AT shalyginev onamechanismofpolarizationoriginatthepolarregionsofjupiter AT velikodskyyui onamechanismofpolarizationoriginatthepolarregionsofjupiter |