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Zasova L.V., Shakun A.V. , Khatuntsev I.V., Ignatiev N.I,(1,2), Brekhovskih U.A.(1), Piccioni G.
(3), Drossart P.(4).
(1) IKI RAS, Moscow, (2) MIPT, Dolgoprudny, Russia,(3) lAPS-INAF, Rome, Italy, (4) LESIA, Meudon, France
O2 night airglow in Venus atmosphere and dynamics around 100 km from
VIRTIS-M VEX
MS3, 3-12.10.2012
O2 Venus night airglow as a tracer of circulation near mesopause
O + O + CO2 --> O2* + CO2 + 5.17 eV - recombination
O2* --> O2 + hv - de-excitation
O2* + M --> O2 + M - quenching
Subsolar-to-antisolar circulation (SS - AS) in thermosphere Retrograde zonal superrotation (RZS) in mesosphere
RGB image . One
60 80
Elevation above the surface: 1- 0, 2 – 40, 3 – 60, 4 – 80, 5 – 90, 6 -100, 7 – 120 km
040 100
120
4 3 2 1
b26
b27
b28
1,2 (black,red) –limb spectra – only O2 emissions bands. 3-4 (green, blue) – on the disk of the planet, peaks of thermal emission of low atmosphere and surface. 1.27 µm peak is a superposition of the non-LTE O2 and thermal emissions. Max O2 -1.269 µm , max thermal radiation – 1.277 µm
VIRTIS-M is mapping spectrometer with spectral range 0.3 -5.1 µm. Spectral resolution in IR of 0.016 µm at 1.27 µm . Two modes of work – nadir and limb. Data – cubes: two coordinates of point + spectrum
Examples of the O2 vertical profilesH,km
Volume emission rateW/m2/m/sr
– MR units conversion coefficient
aRl
dInhkdI
kB
OHcl
MR2
)(),,()(
4
3
2
2
1
Equation for the O2 intensity calculation:
.221,13.1,3.1,23.1 4321
MRk
875.0a – Lambert cloud albedo (Crisp et al. [1996]) ),,(
2OHcl nhk – aspect ratio 1.27 /1.18 of thermal emission of the atmosphere
l – path in the layer )0( R – path in the layer )0(
)(I - VIRTIS-M measured spectral intensity
Thermal emissionIntensity at 1.27 µm
It was chosen 27 areas without visible O2 emission. They occur in the range of surface altitudes from -2 km to +2.5 km. Measured spectra were corrected for errors, not taken into account in calibration procedure. Spectra for these areas were fitted by modeled ones by variation of clouds opacity and the H2O mixing ratio. Surface elevation was taken from Magellan data.
Example of fitting spectra.Measured (triangles) and synthetic spectra (solid line), orbit 320
The importance to take into account altimetry
Magellan altimetry The O2 emission distribution with k=const. Artifacts due to surface elevation features are seeing in the O2 distribution
The O2 emission distribution with k=k(h). Artifacts disappeared.
6MR
Orbit 66 (data cubes 00, 01)Maximum emission at AS area Subsolar-antisolar flow
Orbit 82 (data cubes 00,01,03)Maximum at 22 h shifted in opposite direction to RZS
Orbit 108-01, 121-01Maximum at 2-3 h in equatorial regionRZS with up to 60 m/s
Orbit 319 (data cubes 01,02)Maximum emission at 23 h at equatorshifted in opposite direction to RZS
RZS
0
-20
-40
φ°
φ°φ°
φ°
(X-axis –local time, unique for all plots)
MAPS of theO2 1.27 μm night airglow
6MR
40
50
60
φ � ,S
-2 -1 0 1 2 LT,h
Orbit 351
321 (00,01)
351 (00 -05)
367 (02)Several maxima1-2.5 h, 4-6 MRRZS up to 60m/s
Orbit 380 (01-11)LT = -3 ÷ 3hNo symmetry
Two maxima: φ = 5°, LT = 0h, 6 MRφ = -30°, LT = 23 h, 4.5 MR
RZS
Two symmetrical maxima
505 (01-03)388 (09-14)
390 (04-13)
567(04,06,08,12,14)569 (04,06,08,10,12,14)
565 (04,06,12,14)
RZS
579 (00,04,06,08,10,12)
591
593 (00-08)
579 (00,04,06,08,10,12,14)
598 (00-06)
597
RZS
(02,03)
MAP of the O2(a1∆g) airglow based on 718 orbits
Only measurements with exposure ≥ 3 s were used to avoid noisy data (left).Corresponding number of orbits for averaging at each point (right).Iav = 0.35±0.3 MR
Intensity , MR Number of orbits
Latit
ude
Latit
ude
Zonal wind
Mean intensity on the evening side is 0.43 MR
Mean intensity on the morning side is 0.26MR
Intensity of the O2 airglow vs. local time for different latitudinal zones, averaged over 10 ° latitude and 2h local
RZS
Ver
tical
em
issi
on r
ate,
MR
Local time, h
Limb data . Averaged over 10 deg. of latitude and 2h of local timeAt latitude < 40 N maximum of emission is found after midnight, and it may be an effect of zonal retrograde superrotation, at φ > 50N maximum of intensity of O2 airglow is before midnight and minimum after midnight. I =0.45±0.36 MR, Hpeak=97 ± 3km, Half-width= 8 ± 3 km
RZS H, km
W/m2/m/srVolume emission rate
Krasnopolsky (2010), photochemical model, based on 64 reactions
4πIO2 = 0.158 (ΦO/1012)1.14 MR
Observed O2 nightside-mean airglow intensity of 0.35 MR requires the O atoms flux of 2.2·1012 cm-2 s-1
Maximum of 6 MR – 2.4·1013 cm-2 s-1
According to Krasnopolsky (2010), the dayside-mean production of O by photolysis of CO2 above 80 km is 6.4 - 7.0 ·1012 cm-2 s-1 at low and high solar activity, respectively.
It is concluded that the model support the observations of the O2
1.27 µm nightglow with mean intensity less than 1 MR
30 40 50 60 70 80
Latitude,deg
1
2
3
4
- lo
g (
P,b
)
60
70
80
90
Ls=20-90
30 40 50 60 70 80
Latitude,deg
1
2
3
4
60
70
80
90
H, km
Ls = 270 - 310
-log10 (P, bar)
30 40 50 60 70 80
Latitude,deg
1
2
3
4
60
70
80
90
Ls=90-130
-lo
g1
0 (
P,
b)
30 40 50 60 70 80Latitude,deg
1
2
3
4
60
70
80
90
H, km
Ls=200-270
-log10 (P, bar)
20 40 60 80
1
3
5P=0.1mbT1
T2
T3
T4
T, K
20 40 60 80
0.5
2.0
3.5
P=0.2 mbT1
T2
T3
T4
T, K
20 40 60 80
0.2
1.4
2.6
P=0.5mb
T1T2
T3
T4
T, K
20 40 60 80
2
5
8 P=1 mb
T1
T2
T3T4
T, K
20 40 60 80
1
3
5P=0.1mbT1
T2
T3
T4
T, K
20 40 60 80
0.5
2.0
3.5
P=0.2 mbT1
T2
T3
T4
T, K
20 40 60 80
0.2
1.4
2.6
P=0.5mb
T1T2
T3
T4
T, K
20 40 60 80
2
5
8 P=1 mb
T1
T2
T3T4
T, K
Thermal tides (Venera-15, Zasova et.al 2007)
Amplitudes of diurnal (T1 )and simi-diurnal (T2) exceed 5K between 85-100 km at low latitudes
Gravity waves in vertical airglow profiles on the night side of Venus and Earth
1 – Earth2- Venus
Venus
Alti
tude,k
m, E
art
h
Ve
nu
s
Earth
Volume emission rate, kR/km
Gravity waves (Altieri et al. this session)
Pioneer Venus NO map/ VIRTIS O2 map
super rotation
024 22 20LT (hr)
Latit
ude
(°)
0
60
30
-60
-30
No influence of super rotation on O2 emission !Conclusion: we do not understand !
LT,h
Pioneer Venus
SPICAV/VEX
SS-AS
SS-AS
RZS
NO(110-140 km)
O2 (95-105 km)
Bougher et al., 2006
Comparison of NO (Pioneer Venus) and O2 (VIRTIS) distributions
SS-AS
SS-AS
RZS
NO(110-140 km)
O2 (95-105 km)
Bougher et al., 2006
Comparison of NO (Pioneer Venus) and O2 (VIRTIS) distributions
NO – maximum emission around 2h (PV, and PICAV).RZS above 100 km is important , up to 60m/s - Brecht et al. (2011)
Map of the O2 emission intensity(MR) and horizontal wind speed (arrows) –topHorizontal divergence in 10-6 S-1 – bottom panel
- Circulation at mesopause is combination of SS-AS, zonal superrotation and waves activity, relative importance of all components is time variable
- In the map (averaged over 718 orbits) emission maximum is observed at low latitudes, around midnight (20N - 20S, LT=22h- 3h, without absolute maximum in antisolar point) for both nadir and limb measurements
- At individual maps a maximum intensity may be found in the range of local time -4h - +4h. Shift of maximum emission to morning terminator may be connected to superposition of SS-AS and RZS. Opposite shift we don’t understand. Sometimes symmetrical behaviors vs. local time is observed Wave activity also may be responsible for deviation of the O2 distribution from the case SS-AS.
- Low intensity near terminators as well as wide spot of higher intensity around midnight (on average map) indicate on wind flows through terminators from the day side. SS-AS is important mode of circulation
- Comparison with NO night glow distribution (with map, obtained by Pioneer-Venus) show both correlation in some cases and anticorrelation in others.
- O2 and NO emissions are related to different layers in the atmosphere
- To explain observed maps of the O2 emission it needs GCM for mesosphere with included photochemistry
SUMMARY
Вертикальное распределение эмиссии O2 (a1∆g):
Интенсивность эмиссии: 0.45 ± 0.36 МРл
Высота максимума эмиссии: 97 ± 3 км
Ширина профиля на половине максимума эмиссии: 8 ± 3 км