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