lmd_Hourdin2000_abstracts.html

2000 .

J.-L. Bertaux, D. Fonteyn, O. Korablev, E. Chassefière, E. Dimarellis, J. P. Dubois, A. Hauchecorne, M. Cabane, P. Rannou, A. C. Levasseur-Regourd, G. Cernogora, E. Quemerais, C. Hermans, G. Kockarts, C. Lippens, M. D. Maziere, D. Moreau, C. Muller, B. Neefs, P. C. Simon, F. Forget, F. Hourdin, O. Talagrand, V. I. Moroz, A. Rodin, B. Sandel, and A. Stern. The study of the martian atmosphere from top to bottom with SPICAM light on mars express. Planetary and Space Science, 48:1303-1320, October 2000. [ bib | DOI | ADS link ]

SPICAM Light is a small UV-IR instrument selected for Mars Express to recover most of the science that was lost with the demise of Mars 96, where the SPICAM set of sensors was dedicated to the study of the atmosphere of Mars (Spectroscopy for the investigation of the characteristics of the atmosphere of mars). The new configuration of SPICAM Light includes optical sensors and an electronics block. A UV spectrometer (118-320 nm, resolution 0.8 nm) is dedicated to Nadir viewing, limb viewing and vertical profiling by stellar occultation (3.8 kg). It addresses key issues about ozone, its coupling with H ₂O, aerosols, atmospheric vertical temperature structure and ionospheric studies. An IR spectrometer (1.2- 4.8 μm, resolution 0.4-1 nm) is dedicated to vertical profiling during solar occultation of H ₂O, CO ₂, CO, aerosols and exploration of carbon compounds (3.5 kg). A nadir looking sensor for H ₂O abundances (1.0- 1.7 μm, resolution 0.8 nm) is recently included in the package (0.8 kg). A simple data processing unit (DPU, 0.9 kg) provides the interface of these sensors with the spacecraft. In nadir orientation, SPICAM UV is essentially an ozone detector, measuring the strongest O ₃ absorption band at 250 nm in the spectrum of the solar light scattered back from the ground. In the stellar occultation mode the UV Sensor will measure the vertical profiles of CO ₂, temperature, O ₃, clouds and aerosols. The density/temperature profiles obtained with SPICAM Light will constrain and aid in the development of the meteorological and dynamical atmospheric models, from the surface to 160 km in the atmosphere. This is essential for future missions that will rely on aerocapture and aerobraking. UV observations of the upper atmosphere will allow study of the ionosphere through the emissions of CO, CO ⁺, and CO ₂⁺, and its direct interaction with the solar wind. Also, it will allow a better understanding of escape mechanisms and estimates of their magnitude, crucial for insight into the long-term evolution of the atmosphere. The SPICAM Light IR sensor is inherited from the IR solar part of the SPICAM solar occultation instrument of Mars 96. Its main scientific objective is the global mapping of the vertical structure of H ₂O, CO ₂, CO, HDO, aerosols, atmospheric density, and temperature by the solar occultation. The wide spectral range of the IR spectrometer and its high spectral resolution allow an exploratory investigation addressing fundamental question of the possible presence of carbon compounds in the Martian atmosphere. Because of severe mass constraints this channel is still optional. An additional nadir near IR channel that employs a pioneering technology acousto-optical tuneable filter (AOTF) is dedicated to the measurement of water vapour column abundance in the IR simultaneously with ozone measured in the UV. It will be done at much lower telemetry budget compared to the other instrument of the mission, planetary fourier spectrometer (PFS).

P. Defraigne, O. de Viron, V. Dehant, T. Van Hoolst, and F. Hourdin. Mars rotation variations induced by atmosphere and ice caps. Journal of Geophysical Research, 105:24563-24570, October 2000. [ bib | DOI | ADS link ]

Because of the conservation of angular momentum, the atmospheric winds and the mass exchange between the Martian ice caps and atmosphere, associated with the sublimation/condensation process (mainly CO₂), induce seasonal effects on Mars' polar motion, nutation, and length of day (LOD). These effects are computed using the output of a global circulation model of the Martian atmosphere, providing atmospheric pressure fields, ice cap surface pressure fields, and zonal as well as meridional winds. For the LOD variations, total amplitudes (CO₂ and wind effects) of 0.22 ms for the annual wave and of 0.38 ms for the semiannual wave are obtained. These amplitudes are more than one order of magnitude larger than the LOD variations induced by the zonal tides, which are at the level of 10 μs. For the induced polar motion the annual amplitude is ˜11 milliarcseconds (mas), and the semiannual amplitude is ˜3 mas. The effect on the nutations, related to the diurnal forcing, is at the level of 0.1 mas. The differences between the results for a liquid and for a solid core are examined and shown to be 1% of the total effects.

F. Hourdin and J.-P. Issartel. Sub-surface nuclear tests monitoring through the CTBT Xenon Network. Geophysical Research Letters, 27:2245-2248, August 2000. [ bib | DOI | ADS link ]

We present the first evaluation of the atmospheric xenon network to be installed as part of the International Monitoring System (IMS) in the frame of the Comprehensive Test Ban Treaty (CTBT). We show that this network should, by itself, provide a significant contribution to the total efficiency of the IMS. For this evaluation, we introduce an inverse approach based upon the time symmetry of the atmospheric transport of trace species. This approach may find applications in a variety of environmental problems.