Lunar and Planetary Science XLVIII (2017)
1120.pdf
JUPITER: LOW-LATITUDE DEPRESSION OF THE AMMONIA ABSORPTION IN NORTHERN
HEMISPHERE . V. G. Tejfel, V. D. Vdovichenko, A. M. Karimov , P. G. Lysenko, G. A. Kirienko, N. N. Bondarenko, G. A. Kharitonova , V. A. Filippov. Fessenkov Astrophysical Institute, Almaty, Kazakhstan,
([email protected])
Introduction: In 2014 we first detected on Jupiter
a strange depression of the 787 nm ammonia absorption band in the Northern hemisphere at low latitudes
[1,2]. In subsequent years, an existence of this depression was annually confirmed by spectral observations,
although we were noticing its variable character [3].
A special important confirmation of this feature on
Jupiter is a significant depletion of gaseous NH3 discovered recently. It also has been found at the same
low latitudes of the Northern hemisphere in the region
of the NEB with using of the big radio telescope’s
system - Very Large Array (VLA) with high angular
resolution [4] .
New observations and processing: From February
to April of 2016, we carried out a special series of
spectrophotometric observations of Jupiter to continue
the study of the current behavior of the ammonia absorption bands centered at 645 and 787 nm. During
these observations we have obtained more than 2,500
CCD-spectrograms, including the spectra of the central meridian, the GRS, and 12 scans of Jovian disk on
different dates (70 zonal spectra in each scan). The
measurements of the ammonia absorption bands are
certainly rather difficult, since they are overlapped
with more intense methane bands. The 787 nm NH3
absorption band was extracted with using of ratios of
the Jovian spectra to the Saturn’s disk spectrum that
was taken as a reference. «Clear» profiles of the NH3
bands are shown in Figure 1.
24-25.02.2016 NH3 787 nm
1,05
1,020
1,00
Jupiter / Saturn
Residual intensity
24-25.02.2016 SCAN S- N NH3 645 nm
1,040
1,000
0,980
0,960
0,940
0,920
0,90
0,85
0,80
0,900
0,880
635
0,95
640
645
Wavelength, nm
650
655
0,75
780
790
800
Wavelengthm nm
Figure 1 –The NH3 absorption bands after extracting
Figure 2 presents the latitudinal variations of the
NH3 absorption bands’ depths derived from about 800
zonal spectra. The equivalent widths of the bands give
the same picture of latitudinal changes. The depression of the ammonia absorption is more expressed for
the 787 nm NH3 band. It begins almost from the equator, and its maximum occurs at the planetographic
latitude of 100N; then the absorption again increases
approaching to the latitude of 200N. The equivalent
bandwidths corresponding to these latitudes are equal
to 18.7 ± 1.4 A, 14.4 ± 1.0 A and 17.8 ± 0.8A. The
645 nm NH3 absorption band also shows depletion at
the low latitudes of the Northern hemisphere, but it is
less pronounced. At the temperate latitudes of the
Northern hemisphere this band’s absorption is systematically lower than the Southern Hemisphere’s
ones.
Figure 2 – Latitudinal variations of the 645 and 787 nm
NH3 absorption bands’ depths on Jupiter in 2016.
Discussion. The differences of latitudinal variations
for both ammonia absorption bands shown in Figure 2
were qualitatively kept in the past 12 years. So it can
be considered as one of the characteristics of the distribution of the ammonia absorption on Jupiter mainly
associated with the conditions of these two bands’
formation. Figure 3 (in the left) shows equivalent
widths of the 645 and 787 nm NH3 absorption bands
normalized to the zero latitude.
This graph illustrates the observed differences in the absorption of
ammonia, although there is a small depression in the
north of the equator and it is visible from the 645 nm
weaker band. We analyzed the radio map of Jupiter’s
gigahertz radiation [4] in order to compare the observed absorption in the course of such a different
range. For this there were longitudinally averaged the
profiles of brightness temperature at 8 -12 GHz. The
resulting picture is upside-down, and conditionally
displays the variations of the ammonia absorption or
the ammonia gas content. A research of ammonia gas
Lunar and Planetary Science XLVIII (2017)
1120.pdf
in the Jovian NEB in the thermal infrared range leads
to a similar conclusion about the lower abundance [5],
also showing the longitude and time variations of the
ammonia absorption.
the intensity of several absorption bands of methane
and ammonia were measured. Figure 5 shows a histogram for obtained in 2016 normalized to the EZ
values of the equivalent widths and depths of the absorption bands of CH4 619, 702, 725 nm and NH3 645,
787 nm. It can be seen that the behavior of the ammonia bands especially 787 nm is markedly different
from the behavior of the methane absorption bands.
1,2
Figure 3 - Left - Normalized to the EZ equivalent
widths of the NH3 bands; Right – Longitudinally averaged latitudinal variations of the ammonia absorption according VLA map of Jupiter at 8-12 GHz.
Normalized to EZ values
1,1
1,0
0,9
0,8
V STZ
0,7
V SEB
0,6
V
EZ
V
NEB
V
NTZ
0,5
By comparing the observed effects, we, of course,
conclude that it’s necessary to take into account the
fact that the cloud layer does not affect on the passage
of millimeter radiation through the atmosphere, whereas the role of multiple scattering in the clouds may
be significant for the transfer of the visible and infrared radiation.
As a preliminary study, we measured the intensity
of molecular absorption bands of methane and ammonia on a random sample of 10 spectrograms of Jupiter's central meridian for each year from 2005 to 2016,
that is, for the full period of Jupiter’s revolution
around the sun. Figure 3 shows that during this period, the band NH3 787 nm in the NEB remained
weaker than observed in the SEB.
W 645
NH3
W 702
W 725
W 787
NH3
2016
R 619
R 645
NH3
R 702
R 725
R 787
NH3
Absorption bands
Figure 5 – The equivalent widths (W) and depths
(R) of the methane and ammonia absorption bands
normalized to EZ values for 5 jovisn belts in 2016.
Conclusion:We expect a continuation of a more
detailed study of the latitudinal and longitudinal variations of the ammonia absorption bands throughout the
entire period of Jupiter revolution around the sun. It
would be very interesting to compare the data on the
visible absorption bands with the data of infrared and
microwave brightness temperature measurements for
different regions of Jupiter, where the ammonia absorption affects the thermal radiation output.
Acknowledgement: This work was performed in
accordance with the subject of the grant 0073 / GF4
Ministry of Education and Science of the Republic of
Kazakhstan..
22
20
Equivalent width, A
W 619
18
16
14
12
W 787 NH 3 SEB
W 787 NH 3 N EB
10
8
2004
2006
2008
2010
2012
2014
2016
Years
Figure 4 – Temporal variations pf the NH3 7887
nm absorption band in SEB and NEB.
For 5 belts of Jupiter: North and South Tropical zones
(STZ and NTZ), the Southern and Northern Equatorial Belts (SEB and NEB) and Equatorial Zone (EZ)
References:: [1] Tejfel V.G..et al.(2005) As-tron.
and Astrophys.Transactions , 24, 359-363..[2] Tejfel
et al. (2005) Bull.AAS, 37, 682. [3] Bondarenko N.N.
(2013) As-tron. and Astrophys.Transactions, 28, 8186. [4] de Pater I. et al. (216) Science, 352,12901294. [5] Fletcher L.N. et al..(2016 ) Icarus, 278 ,
128-161.