M. De Mazière

Composition of the Venus mesosphere measured by Solar Occultation at Infrared on board Venus Express

Solar Occultation at Infrared (SOIR), which is a part of the Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV) instrument on board Venus Express, combines an echelle-grating spectrometer with an acoustooptical tunable filter. It performs solar occultation measurements in the IR region at a high spectral resolution better than all previously flown planetary spectrometers. The wavelength range probed allows for a detailed chemical inventory of the Venus atmosphere above the cloud layer, with an emphasis on the vertical distribution of the gases. A general description of the retrieval technique is given and is illustrated by some results obtained for CO2 and for a series of minor constituents, such as H2O, HDO, CO, HCl, and HF. Detection limits for previously undetected species will also be discussed.

The study of the martian atmosphere from top to bottom with SPICAM light on mars express

Abstract 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 H2O, 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 H2O, CO2, CO, aerosols and exploration of carbon compounds (3.5 kg). A nadir looking sensor for H2O 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 O3 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 CO2, temperature, O3, 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 CO2+, 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 H2O, CO2, 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).

Ground-based visible measurements at the Jungfraujoch station since 1990

Ground-based observations of nitrogen dioxide and ozone total columns have been performed since June 1990 at the International Scientific Station at the Jungfraujoch (45°N, 8°E). Measurements are made twice a day, at sunrise and sunset, by looking at the sunlight scattered at zenith in the visible range. NO2 and O3 vertical abundances are deduced by the differential absorption method. The error sources of the method are discussed in detail. For most observation conditions, the precision of measurement is estimated at about 11% for NO2 and 6% for O3. However larger errors might be encountered occasionally due to tropospheric pollution or enchanced multiple scattering in thick clouds. It is shown that the signature of such events can be detected in the evolution of the retrieved vertical column during the twilight period. A systematic method to detect and reject data significantly biased is described and applied to the NO2 time-series of measurements.

Combined characterisation of GOME and TOMS total ozone measurements from space using ground-based observations from the NDSC

Several years of total ozone measured from space by the ERS-2 GOME, the Earth Probe TOMS, and the ADEOS TOMS, are compared with high-quality ground-based observations associated with the Network for the Detection of Stratospheric Change (NDSC), over an extended latitude range and a variety of geophysical conditions. The comparisons with each spaceborne sensor are combined altogether for investigating their respective solar zenith angle (SZA) dependence, dispersion, and difference of sensitivity. The space- and ground-based data are found to agree within a few percent on average. However, the analysis highlights for both GOME and TOMS several sources of discrepancies: (i) a SZA dependence with TOMS beyond 80° SZA; (ii) a seasonal SZA dependence with GOME beyond 70° SZA; (iii) a difference of sensitivity with GOME at high latitudes; (iv) a difference of sensitivity to low ozone values between satellite and SAOZ sensors around the southern tropics; (v) a north/south difference of TOMS with the ground-based observations; and (vi) internal inconsistencies in GOME total ozone.

Ground‐based observations of stratospheric NO2 at high and midlatitudes in Europe after the Mount Pinatubo eruption

Nitrogen dioxide has been monitored at the International Scientific Station at the Jungfraujoch (46°N, 8°E) since June 1990 and at Sodankyla (67°N, 27°E) since January 1990. NO 2 vertical column abundances are measured during the morning and evening twilights by application of the differential absorption method using the sunlight scattered at zenith in the visible range. The available time series shows a significant reduction of NO 2 starting in winter 1992, after the eruption of the Mount Pinatubo volcano. A maximum decrease of about 35% is observed in January 1992 at both stations. The continued series of observations shows the recovery of the NO 2 column until August 1995. These results are compared with two-dimensional chemical model calculations, including the effect of heterogeneous reactions on observed Pinatubo aerosols. In general, the modeled NO 2 columns agree qualitatively with the observations although the amplitude of the seasonal variation is underestimated, possibly due to internal limitations of the model which, for example, does not include diurnal changes. The observed and calculated NO 2 percent changes are in good agreement, which confirms quantitatively the impact of the heterogeneous chemistry on stratospheric NO 2 .

Analysis of the origin of the distribution of CO in the subtropical southern Indian Ocean in 2007

We show carbon monoxide (CO) distributions at different vertical levels over the subtropical southern Indian Ocean, analyzing an observation campaign using Fourier transform infrared (FTIR) solar absorption spectrometry performed in 2007 at Reunion Island (21°S, 55°E). The CO pollution levels detected by the FTIR measurements during the campaign show a doubling of the CO total columns during the Southern Hemisphere biomass burning season. Using correlative data from the Measurement of Pollution in the Troposphere instrument and back trajectories analyses, we show that the potential primary sources for CO throughout the troposphere in 2007 are southern Africa (June-August) and South America (September-October). A secondary potential contribution from Southeast Asia and Indonesia-Malaysia was identified in the upper troposphere, especially in July and September. We examine the relation between the Asian monsoon anticyclone seasonal cycle and this result. We also investigate the relative contribution of different areas across the globe to the CO concentration in the subtropical southern Indian Ocean in 2007 using backward simulations combining the Lagrangian model FLEXPART 6.2, the Global Fire Emissions Database (GFEDv2.1) and the Emission Database for Global Atmospheric Research (EDGARv3.2-FT2000). We confirm the predominance of the African and South American contributions in the CO concentration in the southern subtropical Indian Ocean below 11 km. We show that CO transported from Australia makes only a small contribution to the total CO concentration observed over Reunion Island, and that the long-range transport of CO coming from Southeast Asia and Indonesia-Malaysia is important, especially from June until September in the upper troposphere.

Evolution of a dozen non-CO2 greenhouse gases above central Europe since the mid-1980s

Abstract High-resolution infrared solar observations have been conducted consistently since the mid-1980s at the International Scientific Station of the Jungfraujoch, Switzerland, by the GIRPAS-ULg team (Groupe Infra-Rouge de Physique Atmosphérique et Solaire-University of Liège), and by colleagues from the Belgian Institute for Space Aeronomy and from the Royal Observatory of Belgium, Brussels. These observations were performed with state-of-the-art Fourier transform infrared (FTIR) spectrometers, revealing specific absorption features of over 20 atmospheric gases in the middle-infrared. Related spectrometric analyses have allowed the derivation of their burdens, seasonal and inter-annual variability, as well as their long-term evolution. In addition to updates of long-term changes for CCl2F2, CHClF2, CH4, N2O, SF6, CO, C2H6 and C2H2 already dealt with at previous Non-CO2 Greenhouse Gases (NCGG) symposia, this paper further reports temporal evolutions observed during the past two decades for a series of other source gases, namely OCS, HCN, CCl3F and CCl4, which also have direct or indirect effects on the radiation balance of the troposphere and on the stratospheric ozone layer.

One-decade trend analysis of stratospheric BrO over Harestua (60°N) and Lauder (45°S) reveals a decline

A trend analysis is performed of stratospheric BrO from ground-based UV-visible observations at Harestua (60°N, 11°E) and Lauder (45°S, 170°E) from 1995 through 2005. At both stations, a positive trend of about +2.5% per year is found for the 1995-2001 period, while a negative trend of about -1% per year is obtained between 2001 and 2005. Given a mean age of air of about 4 ± 1 years, the decline in stratospheric bromine since 2002 follows the decline of tropospheric organic bromine observed since the second half of 1998, as a result of the Montreal Protocol. These findings confirm that the impact of the Montreal Protocol restrictions on brominated substances have now reached the stratosphere. From our study, we have also derived a contribution of 6 ± 4 ppt of the brominated very short-lived substances and inorganic bromine tropospheric sources to the total bromine loading.

An instrumented station for the survey of ozone and climate change in the southern tropics

The assessment of changes induced by human activities on Earth atmospheric composition and thus on global climate requires a long-term and regular survey of the stratospheric and tropospheric atmospheric layers. The objective of this paper is to describe the atmospheric observations performed continuously at Reunion Island (55.5 degrees east, 20.8 degrees south) for 15 years. The various instruments contributing to the systematic observations are described as well as the measured parameters, the accuracy and the database. The LiDAR systems give profiles of temperature, aerosols and ozone in the troposphere and stratosphere, probes give profiles of temperature, ozone and relative humidity, radiometers and spectrometers give stratospheric and tropospheric integrated columns of a variety of atmospheric trace gases. Data are included in international networks, and used for satellite validation. Moreover, some scientific activities for which this station offers exceptional opportunities are highlighted, especially air mass exchanges nearby dynamical barriers: (1) On the vertical scale through the tropical tropopause layer (stratosphere-troposphere exchange). (2) On the quasi-horizontal scale across the southern subtropical barrier separating the tropical stratospheric reservoir from mid- and high latitudes.

BARCOS, an automation and remote control system for atmospheric observations with a Bruker interferometer

In order to make long-term monitoring of the atmospheric composition using commercial Bruker Fourier transform spectrometers more cost effective, a system called BARCOS has been developed. The system enables one to perform the operation of the spectrometric atmospheric observations in a remotely controlled or autonomous way, without human presence at the measuring site. Several observation geometries are foreseen, including solar and lunar absorption spectrometry. BARCOS is built using existing commercial hardware and software components, including the Bruker software for the operation of the spectrometer (OPUS) and runs in a personal computer (Microsoft) environment. It includes a small meteorological station. It is a flexible system, allowing manual interventions at any time. To run BARCOS effectively, the only prerequisite is that internet access is available at the site of operation. This article describes the BARCOS system hardware and software configurations.