Non-LTE emission from VIRTIS/Venus Express observations

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Non-LTE emission from VIRTIS/Venus Express
observations

• Pierre Drossart1
• With Giuseppe Piccioni2,
• Gabriella Gilli3, M. Lopez-Valverde3, Raphaël
  Garcia4 and the VIRTIS/VEX team

1LESIA, Observatoire de Paris 2IAPS, CNR, Rome
3IAA, Granada, 4 IRAP, Toulouse
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Launch 9 November 2005 Orbit insertion 11
April 2006 Today 2364 orbits
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VIRTIS for Venus Express 7 years after P.
Drossart, G. Piccioni in mem. A. Coradini
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Aeronomy of Venus

• The upper atmosphere of planets exhibit a large
  variety of physical processes, essential to
  understand the interaction of a planet with its
  environment, but these regions are difficult to
  sound, and still relatively poorly explored!

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O2 average emission (L. Soret and JC. Gérard ,
Liège)
O2 emission altitude 95 km
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VIRTIS O2 Herzberg II spectrum obs.
Cf Migliorini et al O2 emission altitude 95
105 km Mean spectrum, obtained by averaging
about 8700 spectra, acquired in the period
17-03-2010 28-02-2011. Identification of 8
Herzberg II bands. In addition, 3 Chamberlain
bands are observed.
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OH and O2 emission on Venus
OH altitude emission 95 km as O2 cf Piccioni
et al 2009
A.V. Shakun, PhD Thesis 2012
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NO observations from VIRTISon VenusGarcia-Munoz
et al, PNAS, 2009
NO altitude (from UV/SPICAV) 110 km
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Basics on non-LTE models for Venus, Mars and the
Earth 1) CO
CO 4.7 µm levels scheme
CO 4.7 µm Vibrational temperatures
Gilli et al. 2011
LTE breakdown for CO(2) occurs at higher
pressure then CO(1) in the 3 planets
FB and FH bands main bands responsible for the
4.7 µm emission
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Results from CO 4.7 ?m analysis (I)

• Rotational lines identified according to the
  spectral resolution of the instruments

Formisano et al. 2005
Formisano et al.2005
Mars 80-110km

• In Mars and Venus, FH lines dominate the
  emission at 100 km, FB becomes optically thin in
  the upper layers

• On the Earth the FB is optically thin at all
  altitudes, due to the smaller abundance of CO.

Funke et al. 2007
Venus 100 km 150 km
Earth 68 km
Funke et al 2005
Gilli et a. 2011
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Results from CO 4.7?m analysis (I)

• Emitted radiance proportional to the amount of
  emitters in opt. thin condition
• FB, and FH lines saturated in the mesosphere of
  Venus and Mars (opt. thick condition)
• FH and FB band do not saturate at any altitudes
  on the Earth

Gilli et al. 2011
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Results from CO 4.7 ?m analysis (II) (focus on
Venus and Mars)
80-110 km
100 km
150 km
Gilli et al. 2011
Data-model comparison for the first time at 4.7
?m. Good overall agreement. In Mars the residuals
are within the noise level The knowledge of the
actual thermal structure on Venus and Mars is
required
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Results VIRTIS-H CO density (I)
Difficult to find spatial and diurnal variation,
due to the irregular distribution of the data
Local time variations
No significant variations with Local Time
observed in this latitude box
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Basics on non-LTE models for Venus, Mars and the
Earth 2) CO2
CO2 4.3 ?m levels scheme

• FB band Transition from 001 level to the ground
• FH, SH bands arises from higher energy states

CO2 high energy states directly excited during
daytime by solar absorption.
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Comparative planetology atmosphere of the
terrestrial planets

• SIMILARITIES
• UV, soft X-rays absorption in the Thermosphere
• IR absorption in the mesosphere

• DIFFERENCES
• Venus and Mars thermosphere colder than on the
  Earth
• O, CO about 10 times more abundant on Venus and
  Mars
• Stronger cooling in the upper regions of Mars
  and Venus by the CO2 15-?m vibrational excited
  levels
• CO2 vmr on the Earth is 1000 time smaller

1. Limb data from VIRTIS/Vex, PFS/Mex (Formisano et
   al. 2005) and results from MIPAS/Envisat (Funke
   et al. 2007) were used.
2. Non-LTE models for Venus (Roldan et al. 2000,
   López-Valverde et al. 2007), for Mars
   (Lopez-Puertas and Lopez Valverde 1994) and for
   the Earth (Lopez-Puertas et al. 2005)

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Basics on non-LTE models for Venus, Mars and the
Earth
CO2 4.3 ?m Vibrational temperatures

• LTE departure at similar pressure levels for
  Mars and Venus, lower pressure on Earth
• Vibrational temperatures constant at the top of
  the atmosphere

Lopez-Valverde, Gilli, PSS, 2011
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VIRTIS observations for CO2 non-LTE
Gilli et al, JGR 2009
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VIRTIS-M maps
CO2 4.3-?m non-LTE measurements
VIRTIS-M spectra profiles
Gilli et al. JGR, 2009
- CO2 emission peak around 110-120 km - Higher
emission at lower SZA

• good S/N up to 160 km
• Change in the overall shape of the band with
  altitude
• The altitude peak is maximum at the centre of the
  band (4.32 ?m)

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R. Garcia, 2011
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Venus as seen by Akatsuki on 6 December 2010 from
600 000 km (UV- 380 nm)