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Perot K.,University of Versailles | Hauchecorne A.,University of Versailles | Montmessin F.,University of Versailles | Bertaux J.-L.,University of Versailles | And 4 more authors.
Atmospheric Chemistry and Physics | Year: 2010

GOMOS (Global Ozone Monitoring by Occultation of Stars), on board the European platform ENVISAT launched in 2002, is a stellar occultation instrument combining four spectrometers and two fast photometers which measure light at 1 kHz sampling rate in the two visible channels 470-520 nm and 650-700 nm. On the day side, GOMOS does not measure only the light from the star, but also the solar light scattered by the atmospheric molecules. In the summer polar days, Polar Mesospheric Clouds (PMC) are clearly detected using the photometers signals, as the solar light scattered by the cloud particles in the instrument field of view. The sun-synchronous orbit of ENVISAT allows observing PMC in both hemispheres and the stellar occultation technique ensures a very good geometrical registration. Four years of data, from 2002 to 2006, are analyzed up to now. GOMOS data set consists of approximately 10 000 cloud observations all over the eight PMC seasons studied. The first climatology obtained by the analysis of this data set is presented, focusing on the seasonal and latitudinal coverage, represented by global maps. GOMOS photometers allow a very sensitive PMC detection, showing a frequency of occurrence of 100% in polar regions during the middle of the PMC season. According to this work mesospheric clouds seem to be more frequent in the Northern Hemisphere than in the Southern Hemisphere. The PMC altitude distribution was also calculated. The obtained median values are 82.7 km in the North and 83.2 km in the South. Source


Altwegg K.,University of Bern | Balsiger H.,University of Bern | Calmonte U.,University of Bern | Hassig M.,University of Bern | And 12 more authors.
Planetary and Space Science | Year: 2012

During the Rosetta flyby at asteroid Lutetia the ROSINA instrument tried to detect a thin exosphere of the asteroid. Although the instrument is sensitive enough to detect even very tenuous gases at a density level of 1 cm -3 the Lutetia exosphere could not be unambiguously detected due to spacecraft outgassing, which was not constant because of the changing solar aspect angle. An upper limit for a water exosphere density at the flyby distance of 3160 km of (3.5±1.0)×10 3 cm -3 was deduced from the measurements. © 2011 Elsevier Ltd. Source


Hassig M.,University of Bern | Altwegg K.,University of Bern | Balsiger H.,University of Bern | Berthelier J.J.,LATMOS | And 6 more authors.
Planetary and Space Science | Year: 2013

The likelihood that comets may have delivered part of the water to Earth has been reinforced by the recent observation of the earth-like D/H ratio in Jupiter-family comet 103P/Hartley 2 by Hartogh et al. (2012). Prior to this observation, results from several Oort cloud comets indicated a factor of 2 enrichment of deuterium relative to the abundance at Earth. The European Space Agency's Rosetta spacecraft will encounter comet 67P/Churyumov-Gerasimenko, another Jupiter-family comet of likely Kuiper belt origin, in 2014 and accompany it from almost aphelion to and past perihelion. Onboard Rosetta is the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) which consists of two mass spectrometers and a pressure sensor (Balsiger et al.; 2007). With its unprecedented mass resolution, for a space-borne instrument, the Double Focusing Mass Spectrometer (DFMS), one of the major subsystems of ROSINA, will be able to obtain unambiguously the ratios of the isotopes in water from in situ measurements in the coma around the comet. In this paper we discuss the performance of this sensor on the basis of measurements of the terrestrial hydrogen and oxygen isotopic ratios performed with the flight spare instrument in the lab. We also show that the instrument on Rosetta is capable of measuring the D/H and the oxygen isotopic ratios even in the very low density water background released by the spacecraft. This capability demonstrates that ROSINA should obtain very accurate isotopic ratios in the cometary environment. © 2013 Elsevier Ltd. Source


Gronoff G.,NASA | Wedlund C.S.,BIRA IASB
IEEE Transactions on Plasma Science | Year: 2011

The Planeterrella is a space plasma simulator, based on Kristian Birkeland's historical experiment, the Terrella. This device not only makes it possible to simulate interactions between an electrode and a magnetized sphere in many different geometries but also to simulate interactions between two magnetized spheres. Such configurations allow the visualization of phenomena unknown to Birkeland, such as an emitting body (Io) immersed in a magnetosphere (Jupiter) or the aurora on the night side of a planet where one magnetic pole points toward the Sun (Uranus). © 2006 IEEE. Source


Ceulemans K.,BIRA IASB | Compernolle S.,BIRA IASB | Peeters J.,Catholic University of Leuven | Muller J.-F.,BIRA IASB
Atmospheric Environment | Year: 2010

BOREAM, a detailed model for the gas-phase oxidation of α-pinene and its subsequent formation of Secondary Organic Aerosol (SOA), is tested against a large set of SOA yield measurements obtained in dark ozonolysis experiments. For the majority of experiments, modelled SOA yields are found to agree with measured yields to within a factor 2. However, the comparisons point to a general underestimation of modelled SOA yields at high temperatures (above 30 °C), reaching an order of magnitude or more in the worst cases, whereas modelled SOA yields are often overestimated at lower temperature (by a factor of about 2). Comparisons of results obtained using four different vapour pressure prediction methods indicate a strong sensitivity to the choice of the method, although the overestimated temperature dependence of the yields is found in all cases. Accounting for non-ideality of the aerosol mixture (based on an adapted UNIFAC method) has significant effects, especially at low yields. Our simulations show that the formation of oligomers through the gas-phase reactions of Stabilised Criegee Intermediates (SCI) with other molecular organic products could increase the SOA yield significantly only at very low relative humidity (below 1%). Further tests show that the agreement between model and measurements is improved when the ozonolysis mechanism includes additional production of non-volatile compounds. © 2010 Elsevier Ltd. Source

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