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Search Results: 1 - 10 of 461775 matches for " A. Hauchecorne "
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Evidence for long-lived polar vortex air in the mid-latitude summer stratosphere from in situ laser diode CH4 and H2O measurements
G. Durry,A. Hauchecorne
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2005,
Abstract: A balloon borne diode laser spectrometer was launched in southern France in June 2000 to yield in situ stratospheric CH4 and H2O measurements. In the altitude region ranging from 20km to 25km, striking large spatial structures were observed in the vertical concentration profiles of both species. We suggest these patterns are due to the presence of long-lived remnants of the wintertime polar vortex in the mid-latitude summer stratosphere. To support this interpretation, a high resolution advection model for potential vorticity is used to investigate the evolution of the Arctic vortex after its breakdown phase in spring 2000.
Evidence for long-lived polar vortex air in the mid-latitude summer stratosphere from in situ laser diode CH4 and H2O measurements
G. Durry,A. Hauchecorne
Atmospheric Chemistry and Physics Discussions , 2005,
Abstract: A balloon borne diode laser spectrometer was launched in southern France in June 2000 to yield in situ stratospheric CH4 and H2O measurements. In the altitude region ranging from 20 km to 25 km, striking large spatial structures were observed in the vertical concentration profiles of both species. We suggest these patterns are due to the presence of long-lived remnants of the wintertime polar vortex in the mid-latitude summer stratosphere. To support this interpretation, a high resolution advection model for potential vorticity is used to investigate the evolution of the Arctic vortex after its breakdown phase in spring 2000.
Observation and backward trajectory of an inertio-gravity wave in the lower stratosphere
A. Hertzog,C. Souprayen,A. Hauchecorne
Annales Geophysicae (ANGEO) , 2003,
Abstract: A Doppler lidar observation of an inertio-gravity wave in the mid-latitude lower stratosphere is presented. The wave packet characteristics (vertical and horizontal wavenumbers, intrinsic and apparent frequencies) are inferred from the analysis of the hodograph of the horizontal wind fluctuations. Those parameters are used as initial conditions for the calculation of the wave packet trajectory backwards in time in the atmosphere. These calculations are realized by ray-tracing techniques, with background fields (wind and stability) provided by the European Center for Medium-Range Weather Forecasting analyses. Sensitivity tests are performed in order to estimate the robustness of the computed trajectory. It is argued that the generation of the wave has taken place in the upper troposphere, where evidence of large synoptic scale Rossby wave disturbances are found. Our results support the fact that geostrophic adjustment (and possibly shear instabilities) associated with such disturbances could be an effective mechanism for the generation of inertia-gravity waves in the mid-latitude. Key words. Meteorology and atmospheric dynamics, mesoscale meteorology, waves and tides, instruments and techniques
Interannual variability and long term changes in planetary wave activity in the middle atmosphere observed by lidar
A. Hauchecorne,P. Keckhut,M. L. Chanin
Atmospheric Chemistry and Physics Discussions , 2006,
Abstract: The upwelling planetary wave activity (PW) from the troposphere controls the intensity of the equator to pole transport of stratospheric ozone by the Brewer-Dobson circulation and thereby modulates the total ozone content at mid- and high-latitudes. Rayleigh lidar temperature data obtained from 1981 to 2001 at mid-latitude were used to study the interannual variability of PW activity in winter (October to April). The spectrum of stratospheric temperature fluctuations exhibits 2 peaks corresponding to 2 dominant modes of free travelling Rossby waves known as 16 day- and 12 day-waves. The 12 day-wave activity is shown to be anticorrelated with the equatorial QBO wind at 40 hPa. During the period 1981–2000 the global PW activity shows a negative trend for months October to January and a positive trend in March and April.
Exploring the C-X…π Halogen Bonding Motif: An Infrared and Raman Study of the Complexes of CF3X (X = Cl, Br and I) with the Aromatic Model Compounds Benzene and Toluene
Nick Nagels,Dieter Hauchecorne,Wouter A. Herrebout
Molecules , 2013, DOI: 10.3390/molecules18066829
Abstract: The formation of halogen bonded complexes formed between the trifluorohalomethanes CF 3Cl, CF 3Br and CF 3I and the Lewis bases benzene and toluene at temperatures below 150K was investigated using FTIR and Raman spectroscopy. Experiments using liquid krypton as solvent show that for both CF 3Br and CF 3I substantial fractions of the monomers can be involved in 1:1 complexes. In addition, weak absorptions illustrating the formation of 2:1 complexes between CF 3I and benzene are observed. Using spectra recorded at temperatures between 120 and 140 K, observed information on the relative stability was obtained for all complexes by determining the complexation enthalpies in solution. The resulting values for CF 3Br .benzene, CF 3I .benzene and (CF 3I) 2 .benzene are ?6.5(3), ?7.6(2) and ?14.5(9) kJ mol ?1. The values for CF 3Br .toluene and CF 3I .toluene are ?6.2(5) and ?7.4(5) kJ mol ?1. The experimental complexation enthalpies are compared with theoretical data obtained by combining results from MP2/aug-cc-pVDZ(-PP) and MP2/aug-cc-pVTZ(-PP) ab initio calculations, from statistical thermodynamical calculations and from Monte Carlo Free Energy Perturbation simulations. The data are also compared with results derived for other C-X···π halogen bonded complexes involving unsaturated Lewis bases such as ethene and ethyne.
Evidences of thin cirrus clouds in the stratosphere at mid-latitudes
P. Keckhut,A. Hauchecorne,S. Bekki,A. Colette
Atmospheric Chemistry and Physics Discussions , 2005,
Abstract: This study is devoted to the possible presence of cirrus clouds in the stratosphere. Three months of lidar data collected in the south of France (44° N) for detection of stratospheric cirrus are carefully analyzed. Most of the cirrus clouds appear to be located in the troposphere below the dynamical tropopause even when the cloud top is close to the thermal tropopause. Two cirrus are found to be unambiguously located well above the local dynamical tropopause. According to high-resolution PV advection calculations, these two clouds are observed inside air masses that originate from the tropical regions and are then transported rapidly to mid-latitudes through isentropic transport. The air mass history for one case is investigated with a 3-D trajectory model. The back-plumes indicate that the air mass, moist with respect to typical stratospheric air, was transported from the subtropical troposphere to the lowermost stratosphere in 4 days before detection above France. A continuous cooling of 5–10° along the trajectory took place during its transit. This cooling could have been partly responsible for the thin cirrus layer detected.
Isentropic advection and convective lifting of water vapor in the UT – LS as observed over Brazil (22° S) in February 2004 by in situ high-resolution measurements of H2O, CH4, O3 and temperature
G. Durry,N. Huret,A. Hauchecorne,V. Marecal
Atmospheric Chemistry and Physics Discussions , 2006,
Abstract: The micro-SDLA balloonborne diode laser spectrometer was flown twice from Bauru (22° S, Brazil) in February 2004 during HIBISCUS to yield in situ H2O measurements in the Upper Troposphere (UT) and Lower Stratosphere (LS) and in particular in the Tropical Tropopause Layer (TTL). The overall TTL was found warmer (with a subsaturated cold point near –79°C) and the LS moister compared to former measurements obtained in tropical oceanic conditions. The use of specific balloons with a slow descent, combined with the high-resolution of the laser sensor, allowed us to observe in situ in the UT, the TTL and the LS several thin layers correlated on H2O, CH4, O3, temperature and PV. A component of these layers is associated with the isentropic transport into the UT- LS of extratropical stratospheric air masses. Moreover, the examination of temperature and tracer (CH4, O3) profiles gives insights on the potential contribution of convective transport of H2O in the TTL.
Impact of land convection on the thermal structure of the lower stratosphere as inferred from COSMIC GPS radio occultations
S. M. Khaykin,J.-P. Pommereau,A. Hauchecorne
Atmospheric Chemistry and Physics Discussions , 2013, DOI: 10.5194/acpd-13-1-2013
Abstract: Following recent studies evidencing the effect of deep overshooting convection on the chemical composition of the tropical lower stratosphere by injection of tropospheric air across the cold-point tropopause we explore its impact on the thermal structure of the tropical tropopause layer (TTL) and the lower stratosphere using the high-resolution COSMIC GPS radio-occultation temperature measurements spanning from 2006 through 2011. The temperature of the lower tropical stratosphere is shown to display a systematic mean cooling of 0.6 K up to 20 km in the late afternoon in the summer over land compared to oceanic areas where little or no diurnal variation is observed. The temperature cycle is fully consistent with the diurnal cycle and geographical location of deep convective systems reported by the Tropical Rainfall Measurement Mission (TRMM) precipitation radar suggesting strong injection of adiabatically cooled air into the lower tropical stratosphere in the afternoon over tropical continents. But most unexpected is the difference between the southern and Northern Hemispheres, the first displaying systematic larger cooling suggesting more intense convection in the southern than in the northern tropics.
Response of tropical stratospheric O3, NO2 and NO3 to the equatorial Quasi-Biennial Oscillation and to temperature as seen from GOMOS/ENVISAT
A. Hauchecorne,J. L. Bertaux,F. Dalaudier,P. Keckhut
Atmospheric Chemistry and Physics Discussions , 2010, DOI: 10.5194/acpd-10-9153-2010
Abstract: The stellar occultation spectrometer GOMOS (Global Ozone Monitoring by Occultation of Stars) on ESA's Envisat satellite measures vertical profiles O3, NO2 and NO3 with a high long-term stability due to the self-calibrating nature of the technique. More than 6 years of GOMOS data from August 2002 to end 2008 have been analysed to study the inter-annual variation of O3, NO2 and NO3 in the tropics. It is shown that the QBO of the equatorial wind induces variations in the local concentration larger than 10% for O3 and larger than 25% for NO2. Quasi-Biennial Oscillation signals can be found in the evolution of the three constituents up to at least 45 km. We found that NO3 is positively correlated with temperature up to 40 km in the region where it is in chemical equilibrium with O3. Above 40 km, NO3 is no more in equilibrium during night and its concentration is correlated with both O3 and NO2. For O3 and NO2, our results confirm the existence of a transition from a dynamical control of O3 below 28 km with O3 correlated with NO2 and temperature and a chemical/temperature control between 28 and 38 km with O3 anti-correlated with NO2 and temperature. Above 38 km and up to 50 km a regime never described before is found with both O3 and NO2 anti-correlated with temperature. For the NO2/temperature anti-correlation, our proposed explanation is the modulation of the N2O ascent in the upper stratosphere by the QBO and the modulation of the Brewer-Dobson circulation. The oxidation of N2O is the main source of NOy in this altitude region. An enhancement of the ascending motion will cool adiabatically the atmosphere and will increase the amount of N2O concentration available for NOy formation.
Evaluation of balloon and satellite water vapour measurements in the Southern tropical UTLS during the HIBISCUS campaign
N. Montoux,A. Hauchecorne,J.-P. Pommereau,G. Durry
Atmospheric Chemistry and Physics Discussions , 2007,
Abstract: Among the objectives of the HIBISCUS campaign was the study of water vapour in the tropical upper troposphere and lower stratosphere (UTLS) by balloon borne in situ and remote sensing, offering a unique opportunity for evaluating the performances of balloon and satellite water vapour data available at the southern tropics in February-April 2004. Instruments evaluated include balloon borne in situ tunable diode laser spectrometer (μ SDLA) and surface acoustic wave hygrometer (SAW), and remote sensing with a near IR spectrometer (SAOZ) flown on a circumnavigating long duration balloon. The satellite systems available are those of AIRS/AMSU (v4), SAGE-II (v6.2), HALOE (v19), MIPAS (v4.62) and GOMOS (v6.0). In the stratosphere between 20–25 km, three satellite instruments, HALOE, SAGE-II and MIPAS, are showing very consistent results (nearly constant mixing ratios), while AIRS, GOMOS and the SAOZ balloon are displaying a slight increase with altitude. Considering the previous studies, the first three appear the most precise at this level, HALOE being the less variable (5%), close to the atmospheric variability shown by the REPROBUS/ECMWF Chemistry-Transport model. The three others are showing significantly larger variability, AIRS being the most variable (35%), followed by GOMOS (25%) and SAOZ (20%). Lower down in the Tropical Tropopause Layer between 14–20 km, HALOE and SAGE-II are showing marked minimum mixing ratios around 17–19 km, not seen by all others. For HALOE, this might be related to an altitude registration error already identified on ozone, while for SAGE-II, a possible explanation could be the persistence of the dry bias displayed by previous retrieval versions, not completely removed in version 6.2. On average, MIPAS is consistent with AIRS, GOMOS and SAOZ, not displaying the dry bias observed in past versions, but a fast degradation of precision below 20 km. Compared to satellites, the μ SDLA measurements shows systematically larger humidity although this conclusion may be biased by the fact that the balloon flights were carried out intentionally next or above strong convective systems where remote observations from space are difficult. In the upper troposphere below 14 km, all remote sensing measurements (except MIPAS of limited precision, and AIRS/AMSU) become rare, dry biased and less variable compared to ECMWF, but particularly HALOE and SAGE-II. The main reason for that is the frequent masking by clouds within which no remote measurements could be performed except by the AMSU microwave. Water vapour remote sensing profiles are represent
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