GOMOS: Gobal Ozone Monitoring by Occultation of Stars

In this paper we report on the progress and status of the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument, and imaging spectrometer under development for flight on the European Space Agency's Polar Orbiting Earth Mission (POEM-1) mission in 1998. Employing occultation of stars as a light probe of the Earth's atmosphere from a sun-sychronous polar orbit, the instrument will monitor ozone and other atmospheric trace gases over the entire globe. Atmospheric transmission resolution of approximately 1.7 km. When data are combined regionally, it will be possible to detect ozone concentration trends as small as 0.05 percent/year, depending on the degree of combination

Vertical structure and size distributions of Martian aerosols from solar occultation measurements

Solar occultations performed with a spectrometer on board the Soviet spacecraft Phobos 2 (Blamont et al. 1991) provided data on the vertical structure of the Martian aerosols in the equatorial region (0[deg]-20[deg] N latitude) near the northern spring equinox (LS = 0[deg]-20[deg]). All measurements were made close to the evening terminator. Five clouds were detected above 45 km altitude and their vertical structure recorded at six wavelengths between 0.28 and 3.7 [mu]m. They have a small vertical extent (3-6 km) and a vertical optical depth less than 0.03. The thermal structure, as derived from saturated profiles of water vapor observed by our instrument in the infrared, does not allow the CO2 frost point to be reached at cloud altitude, strongly suggesting that cloud particles are formed of H2O ice. Under the assumption of spherical particles, a precise determination of their effective radius, which varies from cloud to cloud and with altitude, is obtained and ranges from 0.15 to 0.85 [mu]m; an estimate of the effective variance of the particle size distribution is ~ 0.2. The number density of cloud particles at the peak extinction level is ~1 cm-3. Dust was also observed and monitored at two wavelengths, 1.9 and 3.7 [mu]m, on nine different occasions. The top of the dust opaque layer, defined as the level above which the atmosphere becomes nearly transparent at the wavelengths of observation, is located near 25 km altitude, with variations smaller than +/-3 km from place to place. The scale height of dust at this altitude is 3-4 km. The effective radius of dust particles near the top of the opaque layer is 0.95 +/- 0.25 [mu]m and increases below with a vertical gradient of ~0.05 [mu]m km-1. Assuming that particles are levitated by eddy mixing, the eddy diffusion coefficient, K, is found to be ~106 cm2 sec-1 at 25 km and 105-106 cm2 sec-1 at 50 km using, respectively, dust and cloud observations. An effective variance of 0.25 (+/-50%) for the dust size distribution is obtained on the basis of a simple theoretical model for the observed vertical gradient of the effective radius of dust particles. Three clouds observed by Viking at midlatitude during the northern summer are reanalyzed. The analysis gives K [approximate] 106 cm2 sec-1 below 50 km altitude and at least 107 cm2 sec-1 above. Since the clouds seen from Phobos 2 are observed at twilight, which coincides with the diurnal maximum of the ambient temperature, they can be assumed to be in a steady state. If their thermodynamic state were to vary quickly during the day, our optical thickness at twilight would correspond to unrealistic values in earlier hours when the temperature is lower. Clouds are well fitted by theoretical profiles obtained assuming the steady state. An atmospheric temperature of 165-170 K at ~50 km is inferred. The negative temperature gradient above the cloud is large (1.5-2 K km-1). A parallel is established between these thin clouds and the polar mesospheric clouds observed on Earth. It is shown that upwelling in equatorial regions at equinox could be a significant factor in levitating cloud particles.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30061/1/0000431.pd

Astrochemistry - Complex organic matter in Titan's aerosols? Reply

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62938/1/nature05418.pd

Quantifying the Martian geochemical reservoirs: An interdisciplinary perspective

International audienc

Isotopic Fractionation of O and C in the Photochemical Escape of Early Mars

International audienceThe isotopic ratios of 13C/12C and 18O/16O on Mars record important information on the atmosphere evolution of the planet. In this work, a 3-D Monte Carlo Model is used to investigate the isotope fractionation effects of C and O in photodissociation (PD) and dissociative recombination (DR) escape processes. Theoretical ionosphere and thermosphere structures corresponding to solar activity levels 2.5, 3.8, and 4.1 Gyrs ago are considered. The contribution of secondary energetic particles to the isotopic fractionation effect is also considered in this work. Our work shows that the Rayleigh fractionation factors in these escape processes depend on solar XUV levels. Using the calculated fractionation factors, we trace the evolution of Mars atmosphere and conclude that 180 mbar CO2 and 360 mbar H2O ( 10m GEL of water) could have been lost to space due to these studied escape processes since 4.5 Gyrs ago. The atmospheric escape and isotope fractionation effects of C and O are more efficiency compare to previous work

Wind measurements in Mars' middle atmosphere at equinox and solstice: IRAM Plateau de Bure interferometric CO observations

Characterizing the Martian atmosphere is an essential objective to understand its meteorology and its climate. The lower atmosphere (< 40 km) and middle atmosphere (40-80 km) of Mars appear dynamically coupled at much higher levels than in the case of the Earth. The vertical extension of the weather phenomena is considerable with for example Hadley's cells reaching the top of the neutral atmosphere (120 km). The circulation in the middle atmosphere modifies the meteorology of the lower atmosphere, affecting the transport and climatic processes Observations of the CO rotational lines at millimeter (mm) wavelengths (Clancy et al 1990) have strongly contributed in the study of the vertical distribution of this compound and the thermal profile in the atmosphere of Mars over 0-70 km. Singledish observations of the CO Doppler lineshift have allowed direct wind measurements in the martian middle atmosphere near 50 km altitude (Lellouch et al 1991), but at a low spatial resolution (12'') enabling only an essentially hemispheric resolution of the martian disk. The use of mm interferometry has allowed us to better spatially resolve the Martian disk, in order to obtain wind maps of the middle atmosphere (Moreno et al 2001)