Study of the Martian atmosphere in the SPICAM IR experiment on Mars-Express

А. Fedorova1,2, A.Trokhimovsky1,2, L.Maltagliati3,4, S.Guslyakova1,2, O. Korablev1,2,

F. Montmessin3, J.L. Bertaux3, A.Reberac3 and the SPICAM team,

1Space Research Institute, Moscow, Russia; 2Moscow Institute of Physics and Technology (MIPT); 3LATMOS, France; 4LESIA, OBSPM, Meudon, France.

3MS3, Moscow, 8-12 October, Russia

Martian atmosphere in short Pressure = 6 mbar , CO2 @ 95 %

(varies with season since atmosphere condenses on the ground)

Mean Surface Temperature = -50°C Low water vapor content = several

tens of micrometers in the atmosphere, but large surface reservoirs (polar caps)

Suspended Particles ( ~ 0.2) :– Dust from the regolith: strong heating

power (like desert dust)– Global dust storms ( ~ 5-10)– Ice crystals (H2O, CO2): from condensation

(cirrus type)

Earth-like Circulation: – Hadley Cell @ solstices – Strong signal of stationary and transient

waves at mid-to-high latitudes in fall/winter

MARS-Express

It was inserted into Mars orbit on 25 December 2003.

4.5 Martian Years of observations: from MY26, Ls 330 (January 2004) to MY 31, Ls 200 (September 2012)

The possibility of continuous study of the atmospheric processes for a long period of time

SPICAM is a one of seven instruments onboard of Mars-Express.

• UV spectrometer (118-320 nm)• IR spectrometer (1-1.7 µm; 0.7 kg)

• Nadir viewing (day side)– H2O abundance at 1.38 μm– H2O and CO2 ices– O2 dayglow

• Solar occultation– CO2, aerosols, H2O

• Limb– Airglow in IR (O2

1Δg 1.27 μm)– aerosols

SPICAM IR – AOTF spectrometer:

O21Dg

CO2 iceH2O ice

H2O

*

*

ОрбитаКА

Звезда

МарсНочная сто

рона

Звезда

Надир

Солнце

Лимб

Spectral range: 1-1.7 µmResolving power: 2000Spectral resolution: 3.5 cm-1

0.5-1.2 nmFOV nadir: 1° solar occultation: ~0.07°

Different observation modes

MONITORING OF WATER VAPOUR (2004-2011)SPICAM IR nadir measurements

The Current Picture of water vapor cycle

Studies and modeling of water cycle : Davies [1981], Jakosky [1983], Haberle & Jakosky [1990], Houben et al. [1997], Richardson & Wilson [2002]; Montmessin et al., 2004; Forget et al., 2006; Montmessien et al., 2007 etc.o Transport of water between hemisphereso The role of water clouds in the hemispheric asymmetry

(Montmessin et al., 2004)o The example: the role of transport in the deposition of

water in the polar caps: perennial water ice at the south pole of Mars could have a precession-controlled mechanism. The GCM shows that 21,500 years ago, when perihelion occurred during northern spring, water ice at the north pole was no longer stable and accumulated instead near the south pole with rates as high as 1 mm yr-1

(Montmessin et al., 2007)

The first observations of water vapour cycleMAWD/Viking (1977-1979)The Global asymmetry of present Mars climateThe Northern summer is in 6 times more water than in the southern summerOnly 10-20 precipitated μm corresponds to 1-2 m3 of ice!

TES / Mars Global Serveyor (1999-2004)The reference map of water vapor seasonal cycle for the General Circulation modeling. The asymmetry is changed. Interannual variations of water vapor

7

WATER IN MARS ATMOSPHERE: RECENT DATA SETS The search of interannual variability Search of daily and spatial variations, condensation and evaporation processes

Mars-Express and MGS experiments can’t give an information about daily variability but can give information about the interannual and spatial variations

Different measurements from 1977 MAWD, 1999 TES, and 2004 Mars-Express, 2006 MRO. Key to a long-term interannual variability?

BUT Mars-Express has demonstrated that different measurement methods can’t be used for long-term interannual comparison

The simultaneous observations of water vapor by different spectroscopic instruments on MEX from near IR to thermal range shows a different results (Korablev et al., 2006)

Retrieval of water vapour in Martian atmosphere (SPICAM)

• Near IR range (1.38 μm band of H2O) is sensitive to

multiple scattering by aerosols in the atmosphere Dust and ice clouds account for MY27-30 (THEMIS/Mars-Odyssey dust and ice data with correction) Numerical technique for radiative transfer modeling in the dusty atmosphere (SHDOM)

• Uniform mixing of H2O in the atmosphere (up to the saturation level) is assumed

• An important issue is an accurate solar spectrum (Fiorenza and Formisano, 2005), with MAWD data correction .

• Spectroscopic database:HITRAN 2004-2008

• Liny-by-line calculations

• Martian Climate Database V4.3 for temperature-pressure profiles

• To minimize a noise SPICAM spectra were averaged by 10 spectra for a fitting

Dust optical depth from THEMIS (Mars Odyssey) 1075 cm-1 and 825 cm-1 (M. Smith, 2009)

SPICAM spectrum

H2O, pr.mmWater vapour with dust account

Dust optical depth for 1,38 mkm

(“Dust” - ”No dust”)

Influence of dust account on the retrieval procedure

%

Dust single scattering albedo w = 0.971; Asymmetry factor g=0.63

MY29

MY27

MY28

A seasonal map of the H2O distribution by SPICAM

MY30

MY27

MY28

H2O, pr.mm

Ls

Comparison ofMAWD (1977-1979)TES (1999-2004)SPICAM (2004-2009)

The recalculation of MAWD/Viking 1 and 2 measurements in the same 1.38 μm with modern climate database (GCM 2005) and spectroscopic dataset (HITRAN 2008)

A good agreement with SPICAM measurements in the same 1.38 μm band

Annual water vapour cycle by SPICAM IRAll years together H2O, pr.mm

1 km3

of ice

• Good dataset of four Martian years for further analysis• “Nothing” else to add to the retrieval algorithm• New solar spectra, resulted in more then 10 % increase of water vapour abundance for polar cap,

and up to 20% increase for other areas.• For the first time water vapour map taking into account dust-clouds scattering, to be compared with

GCM and other instruments results.

Summary

Example of water vapour loss during global dust storm at MY28

(seasonal dependence for H2O averaged on latitude stripe (-45:-55))

MY27

MY28

O2 NIGHTGLOW ON MARS (2010-2012)

SPICAM IR limb measurements

Deactivation of the emission:

1) The emission at altitudes >20-25 km

O2(a1Dg) O2(X3Sg) + hn ( ~ 4566 s )

2) Deactivation through collision with CO2 CO2 (<20 km)

O2(a1Dg) + CO2 O2(X3Sg)+ CO2

(k2 ~ 10-20 cm3 s-1)

O3 + hn O(1D) + O2(a1Dg) 220 nm < l < 320 nm

The O2 dayglow in 1.27 µm on MarsThe dayside

The O2 emission at 1.27 μm is produced by UV dissociation of ozone

The emission was predicted after the ozone discovery in atmosphere of Mars in spectra recorded by UV spectrometer onboard of Mariner-7 (Barth, 1971). For the first time the emission was detected by Noxon et al. (1976) by means of ground-based telescopes. The maximum values observed in the early spring in both hemispheres are closer to polar regions, reach 30 MR, and its variations reflect variations of the ozone abundance in the atmosphere.

Seasonal distribution from January 2004 (Ls=330o) to May 2006 (Ls=50o)

The nightglow О2 (а1Δg) 1.27 μm on Venus and Mars

The O2 emission was known for a long time The oxygen emission at 1.27 μm at the night

side of Venus is a product of atomic oxygen recombination that in turn is a product of photolysis of CO2 on the dayside and transfers to the nightside by global circulation in the upper mesosphere and thermosphere of Venus which causes the gas motion from subsolar to antisolar point.

Venus

The O2 emission is produced by oxygen recombination

O+O+CO2 O2(a1Dg)+CO2

Mars The O2 emission was not detected directly up to 2010 Atomic oxygen which participates in the reaction, is

formed on the dayside of Mars as a result of CO2 photodissociation by solar UV radiation with a wavelength λ <207.5 nm and transported on the night side by the subsolar-antisolar circulation. The transport to the winter polar region is performed by the Hadley meridional cell.

(Krasnopolsky, Icarus, 2004)

1) Detection of the O2 nightglow on Mars in 2010 in the OMEGA experiment on Mars-Express (Gondet et al., 2010; Bertaux et al., 2011,2012)There were three detections of the O2 nightglow on limb at the South and North Poles. The vertical emission intensity is 0.24 MR

First detection on Mars in 2010

2) Observations of the O2 nightglow on Mars in 2010-2012 by CRISM experiment on MRO (Clancy et al., 2011, 2012)Since July of 2009, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) has obtained limb scans over two orbits at solar longitude (Ls) intervals of ~30°.

The O2 nightglow

O2 nightglow with SPICAM IR This emission is an effective indicator of downward flow of air from the altitudes

where the CO2 photodissociation occurs (i.e. above 70 km). The intensity of the nightglow emission and the altitude of the nightglow layer are controlled by wind magnitudes and eddy diffusion , the key chemical reaction rates.

Since 2010 the OMEGA/MEX does not operate in this spectral range

SPICAM IR Good points:

A campaign of nightglow observations by SPICAM has begun from July 2010 A new command has been used with a maximal integration time of one spectral point

11.2 ms (5.6 ms is a standard for dayside nadir and solar occultations). One ‘window’ in the spectral range of 1260-1280 nm. 2 sec for one spectrum

IR channel of SPICAM/MEX is turned on now during stellar occultations in 2011-2012 and we hope during night limb from summer 2012.

Bad points: low vertical distribution of SPICAM with FOV of 1o , about 20 km at limb near a

pericenter of orbit Low sensitivity is not enough for nadir measurements – only limb measurements can be

done

First observations (2010), MY30, Ls 150-160, the South Pole

First results for the South Pole:1. Vertical resolution for the observations varies

from 20 to 35 km. Deconvolution with the FOV was necessary.

2. Altitude of a peak of the O2 slant emission varies from 37 to 47 km

Vertical distribution of the O2 (a1Δg) volume emission rate in MR/km can be retrieved from the slant emission.

dzRozzzndllnRN

oROOoO

22222 )(2)()(

1. Tikhonov regularization 2. the Richardson-Lucy algorithm

to deconvolve FOV of SPICAM3. an inversion of the O2 volume

emission rate in MR/nm for both deconvolved profiles of slant emission and profiles with the SPICAM original resolution

The Martian general circulation model by LMD (LMD GCM, Lefevre et al., 2004; Millour et al., 2008; version 2012)

• a new Martian general circulation (version 2012)

• Atmospheric circulation, photochemical cycle, upper atmosphere processes and ionosphere

• Plenty of improvementsincluding Improved Dynamics, Convection and Turbulence Model, Improved “dust model” to simulate observed Martian years (MY24 – MY30), IR and solar wavelength radiative effects of clouds, Improved cloud microphysics etc

A new model well reproduce now the current MEX and MRO observations

Comparison of the O2 nightglow with the LMD GCM (Lefevre et al., 2004; Millour et al., 2008; version 2012)

Black - SPICAM observations; Red - OMEGA data

Blue – GCM model (dashed blue – convolved with SPICAM vertical

resolution)

• the altitude of the nightglow maximum for volume emission rate varies from 45 to 55 km, which corresponds on average the model values.

• The vertically integrated emission rate is in 2 times lower than in the model– more intense transport?

Vertical distribution of the atomic oxygen

21

221

2

])[1()]([][

COk

COkOO

D

O + O +CO2 O2(a1Dg)+CO2 (1) Important issue:

the oxygen photochemistry controls the energy budget in the 70 to 130 km altitude range. Atomic oxygen is known to have an important effect on the CO2 15-μm cooling. The underestimation of O content would yield an overestimation of the temperature in the GCM modeling.

2g1

22g1

221

12 (aO(aO1]][][[

)]([COkCOOOk

dtaOd g )D )DD

0~)]([ 1

2

dtaOd gD

2g1

22g1

221 (aO(aO1~]][][[ COkCOOOk )D )D

The steady state is reached, when photochemical equilibrium exists:

The resulting formula for atomic oxygen:

k1 is the rate coefficient of reaction (1), β is the effective yield; k2 is the deactivation rate; τ is radiative lifetime of the excited state

Assuming the vertical distribution of O2(a1Δg) is preliminary controlled by photochemistry. Using appropriate reactions, the equilibrium equation for O2(a1Δg) could be written as:

Oxygen profiles and comparison with the GCM

21

221

2

])[1()]([][

COk

COkOO

D

As the basic values we have taken:1) the kinetics rate of reaction k1(T) = 9.46 × 10−34 exp(485/T)cm6 molecule-1 seс-1 (NIST dataset) ,2) the effective yield β =0.753) deactivation rate k2=10-20 cm3 molecule-1 seс-1

4) radiative lifetime of the excited state τ =4470 sec. 5) Temperature and atmospheric density vertical profiles were are taken from the LMD general circulation model.

Solid lines: observationsDashed lines: LMD GCM modeling

The estimated density of oxygen atoms at altitudes from 50 to 65 km varies from 1.5 1011 to 2.5 1011 cm-3

The O2 nightglow observations (2011-2012)

• 64 observations (from orbit 8302 to 10642) with the O2 nightglow detected at limb for the North Pole from Ls 250 to Ls 360 and the South Pole from Ls 0 to 120.

• Plenty of observations with vertical resolution better than 40 km• The black points are indicated emissions detected at limb • Detection at low latitudes is the O2 day-side afterglow.

Vertical profiles of the O2 emission

• Emission peak at 35-42 km for the North Pole and 45-50 km for the South Pole • The emission is more intense for the North Pole

Seasonal distribution of O2 for the South and North Poles Comparison with the GCM O2-O

MR

The vertically integrated emission rate is totally lower than in the model but the South Pole emission shows more discrepanciesThe maximum of emission is shifted for the season compared to the GCM model

The South Pole Ls 115-160

The North Pole Ls 265-275

The temperature and CO2 density from UV stellar occultationsSimultaneous observations of

atmospheric density

• Warming of the middle atmosphere 40-70 km is more strong (on 20-30K)

The atmospheric downwelling circulation over the Pole, which is part of the equator-to-pole Hadley circulation is more strong than expected?The same results by MCS/MRO McCleese et al.,2008. Not completely improved by the model?• The cold layer at 105 km • The density is much higher

• Good agreement for density• Warming in the middle

atmosphere is well reproduced• Possible cold layer at 120 km

The South Pole

The North Pole

ConclusionsSPICAM IR on MEX is a small instrument performing observations of the Martian atmosphere:1) Mapping of water vapor, search of interannual variability

Good dataset of four Martian years for further analysis

2) The study of the O2 nightglow as a tracer of polar dynamics The estimated density of oxygen atoms at altitudes from 50 to 65 km varies from 1.5 to 2.5 1011 cm-3. The South Pole: the GCM model does not well reproduce the emission, atmospheric density and

temperature profiles in the South Pole night. The North Pole: a good agreement with the model The differences may reflect the current uncertainties in the kinetics of the production of O2(a1Δg), or

can be due to an inaccurate downward transport of O atoms by the GCM in the polar night region (especially for the South Pole).

3) Mapping of O2 dayglow (a tracer of ozone on Mars) Validation of Martian GCM with photochemisty, anticorrelation with water vapour Validation of kinetic parameters

4)Vertical distribution of water vapor form solar occultation on Mars Transport of water, condensation processes Supersaturation has been detected during the northern spring (Maltagliati et al., 2011)

5) Dust and water ice clouds studies from solar occultation Seasonal changes of vertical distribution and particles sizes Impact on the atmospheric heating in the middle atmosphere