Jean-Baptiste Renard

Carbon aerosols and atmospheric photochemistry

Carbon aerosols are produced by all combustion processes. This paper investigates some possible effects of heterogeneous reduction of atmospheric constituents on carbon aerosols. Reduction of HNO 3 , NO 2 , and O 3 on carbon aerosols may be an important effect of increased air traffic that has not been considered to date. It is shown that if HNO 3 , NO 2 and O 3 are heterogeneously reduced on atmospheric amorphous carbon aerosols, then a significant, lower stratospheric ozone loss mechanism could exist. This ozone loss mechanism is almost independent of temperature and does not require the presence of sunlight. The mechanism can operate at all latitudes where amorphous carbon aerosols are present. The relative importance of the mechanism increases with nightlength. The reduction of HNO 3 on carbon aerosols could also be a significant renoxification process wherever carbon aerosols are present. Owing to the very different soot levels in the two hemispheres, this implies that there should be a hemispheric assymetry in the role of these mechanisms. The renoxification leads to simulated tropospheric HNO 3 /NO x ratios that are close to those observed. In contrast to the stratospheric response, the tropospheric production of NO x due to the reduction of HNO 3 would lead to tropospheric ozone production.

Retrieving parameters of the anisotropic refractive index fluctuations spectrum in the stratosphere from balloon-borne observations of stellar scintillation

Scintillation effects are not negligible in the stratosphere. We present a model based on a 3D model of anisotropic and isotropic refractive index fluctuations spectra that predicts scintillation rates within the so-called small perturbation approximation. Atmospheric observations of stellar scintillation made from the AMON-RA (AMON, Absorption par les Minoritaires Ozone et NO(x); RA, rapid) balloon-borne spectrometer allows us to remotely probe wave-turbulence characteristics in the stratosphere. Data reduction from these observations brings out values of the inner scale of the anisotropic spectrum. We find metric values of the inner scale that are compatible with space-based measurements. We find a major contribution of the anisotropic spectrum relative to the isotropic contribution. When the sight line plunges into the atmosphere, strong scintillation occurs as well as coupled chromatic refraction effects.

Polarization of asteroids. Synthetic curves and characteristic parameters

Abstract A data base of polarization measurements has been constituted for about 100 asteroids, mainly observed in the blue and green domains, for which no significant wavelength effect is detected. Individual empirical phase curves have been obtained for about 35 asteroids, using polynomial and trigonometric fits that lead to similar results within the phase angle range where data are available. Phase curves are comparable for asteroids which belong to the same taxonomic type. Significant analogies are found between the three “synthetic” curves drawn for asteroids of igneous type (S, M and E). The analogies are even greater between the three curves obtained for asteroids of C, G and P types that exhibit a deeper minimum of polarization and a steeper slope at inversion than the previous ones. The CCD polarization method, previously developed for comets, has been adapted to polarimetric observations of asteroids (up to magnitude 15) from the Pic du Midi Observatory. The comparison between the synthetic curves and the new data typically allows us to estimate that 1992 AC is an igneous object. Polarimetry is found to be an additional tool to determine the taxonomic superclass, or possibly class, of asteroids that happen to be observed at relatively large phase angles.

First simultaneous global measurements of nighttime stratospheric NO2 and NO3 observed by Global Ozone Monitoring by Occultation of Stars (GOMOS)/Envisat in 2003

The Global Ozone Monitoring by Occultation of Stars (GOMOS) stellar occultation instrument on board the Envisat European satellite provides global coverage of ozone and other stratospheric species with good vertical resolution and a self-calibrating method. In this paper we present the first simultaneous global distribution of stratospheric NO 2 and NO 3 from 1 year of nighttime GOMOS data in 2003. Most previous NO 2 satellite observations have been made using the solar occultation technique. They are difficult to interpret due to the fast photochemical evolution of NO 2 at sunrise and sunset. There are no published observations of NO 3 from space because this constituent is rapidly photodissociated during daytime and is not observable by solar occultation. It is shown that the NO 2 mixing ratio reaches a maximum around 40 km with values between 14 and 16 ppbv at low and middle latitudes. The global distribution of NO 2 observed by GOMOS is very similar to the NO + NO 2 Halogen Occultation Experiment climatology deduced from sunset measurements from 1999 to 2004. At high latitude a high mixing ratio is observed in the north vortex in November 2003 after a strong solar proton event and in the south vortex in July 2003. The NO 3 mixing ratio peaks at 40–45 km. NO 3 follows a semiannual variation at low latitudes with maxima at equinoxes and an annual variation at middle and high latitudes with a maximum in summer. In the upper stratosphere the mixing ratio of NO 3 is strongly correlated with temperature due to the thermal dependence of its formation rate. Citation: Hauchecorne, A., et al. (2005), First simultaneous global measurements of nighttime stratospheric NO 2 and NO 3 observed by Global Ozone Monitoring by Occultation of Stars (GOMOS)/Envisat in 2003

Light scattering by dust particles in microgravity: polarization and brightness imaging with the new version of the PROGRA2 instrument

A new version of the PROGRA2 instrument, dedicated to measuring the polarization phase function of various kinds of solid particles, allows obtaining maps of polarization and brightness with a spatial resolution of a few tens of micrometers. The measurements are conducted in microgravity during parabolic flights to ensure random distribution and orientation of the particles. The results of the first two sessions are presented. Comparison between measurements and Mie theory modeling for glass spheres shows that the instrument works well and that accurate results can be obtained even at small phase angles. Results for irregularly shaped particles are also presented.

Diurnal and nocturnal distribution of stratospheric NO2 from solar and stellar occultation measurements in the Arctic vortex: Comparison with models and ILAS satellite measurements

NO2 mixing ratio profiles were measured at sunset between 14 and 30 km using the Limb Profile Monitor of the Atmosphere (LPMA) experiment and during the night between 13 and 31 km using the Absorption par Minoritaires Ozone et NOx (AMON) experiment inside the Arctic vortex, both on February 26, 1997. Coinciding profiles measured by the Improved Limb Atmospheric Spectrometer (ILAS) instrument on board ADEOS have been used to check the consistency between the satellite and balloon profiles for NO2, O3, and HNO3. A box model has been used for the photochemical correction of the LPMA NO2 profiles at sunset. The resulting NO2 balloon-borne profiles of LPMA and AMON are compared to each other after accounting for the day/night photochemical variation using the box model initialized with measurements. The comparisons thus performed show an average difference less than 9% between the two measurements (considered to sample similar air masses) when the box model is initialized with little chlorine activation (i.e., when the major burden of chlorine is stored in ClONO2) for a 1 day integration. The comparison with the Reprobus 3-D chemistry transport model (CTM) seasonal simulations clearly confirms an underestimation of NO2 by the model below 25 km, in the altitude range where aerosols lead to a complete removal of NOx in the model. Recent updates of rate coefficients for conversion of HNO3 into NO2 only slightly improve the NO2 model results in vortex conditions. These results suggest that a source of NO2 is still lacking in the CTM.

SALOMON: a new, light balloonborne UV–visible spectrometer for nighttime observations of stratospheric trace-gas species

A new, light balloonborne UV-visible spectrometer, called SALOMON, is designed to perform nighttime measurements of stratospheric trace-gas species by using the Moon as a light source. The first flight, performed on 31 October 1998 at mid-latitude with a float altitude of 26.7 km, allowed the performance of the pointing system to be checked and vertical profiles of ozone, NO(2), NO(3), and possibly OBrO to be obtained. First the instrument and then the performance of the pointing system and the detector are described. Finally the vertical profiles are compared with other profiles obtained at the same location five years before with the heavier balloonborne spectrometer AMON, which uses a star as the light source.

Laboratory light scattering measurements on natural particles with the PROGRA2 experiment: an overview

Abstract Polarimetric phase curves were obtained with the PROGRA2 instrument for different particles: glass beads, polyhedral solids, rough particles, dense aggregates and aggregates with porosity higher than 90%. The main purpose of these measurements is to build a large database, which allows interpreting remote sensing observations of solar system bodies. For some samples numerical or experimental models (i.e. DDA, stochastically built particles, microwave analogue) and laboratory experiments are compared to better disentangle the involved physical properties. This paper gives some main results of the experiment, and their applications to Earth atmosphere, comets and asteroids.

Role of lee waves in the formation of solid polar stratospheric clouds: Case studies from February 1997

Recent theories of solid polar stratospheric clouds (PSCs) formation have shown that particles could remain liquid down to 3 K or 4 K below the ice frost point. Such temperatures are rarely reached in the Arctic stratosphere at synoptic scale, but nevertheless, solid PSCs are frequently observed. Mesoscale processes such as mountain-induced gravity waves could be responsible for their formation. In this paper, a microphysical-chemical Lagrangian model (MiPLaSMO) and a mountain wave model (NRL/MWFM) are used to interpret balloon-borne measurements made by an optical particle counter (OPC) and by the Absorption par Minoritaires Ozone et NOx (AMON) instrument above Kiruna on February 25 and 26, 1997, respectively. The model results show good agreement with the particle size distributions obtained by the OPC in a layer of large particles, and allow us to interpret this layer as an evaporating mesoscale type Ia PSC (nitric acid trihydrate) mixed with liquid particles. The detection of a layer of solid particles by AMON is also qualitatively reproduced by the model and is interpreted to be frozen sulfate acid aerosols (SAT). In this situation, the impact of mountain waves on chlorine activation is studied. It appears that mesoscale perturbations amplify significantly the amount of computed ClO, as compared to synoptic runs. Moreover, MiPLaSMO chemical results concerning HNO3 and HCl agree with measurements made by the Limb Profile Monitor of the Atmosphere (LPMA) instrument on February 26 at a very close location to AMON, and explain part of the differences between LPMA measurement and Reactive Processes Ruling the Ozone Budget in the Stratosphere (REPROBUS) model outputs.

Origin of the January–April 2004 increase in stratospheric NO2 observed in the northern polar latitudes

Large increase in stratospheric NO2 content has been observed during the 2003–2004 Arctic winter. The first one, in early November 2003 is well documented and is due to a strong solar protons event. A second event occurred on January 22, 2004, leading to a large amount of NO2 in the lower mesosphere. This second event can be analyzed using data from nighttime satellite measurements performed by the GOMOS and MIPAS instruments onboard Envisat, and by ground based column measurements performed by SAOZ. It seems that in-situ production of NO2 is located at an altitude of around 60 km associated with the precipitation of electrons with energy of a few hundred keV. These electrons originated from the high latitudes magnetosphere, and are associated with a solar coronal mass ejection. Therefore, a particular nighttime chemistry in the lower mesosphere is proposed to explain the measurements.