Publications (17)25.87 Total impact
-
Dataset: A global climatology of the mesospheric sodium layer from GOMOS data during the 2002-2008 period
-
Article: Response of tropical stratospheric O$_3$, NO$_2$ and NO$_3$ to the equatorial Quasi-Biennial Oscillation and to temperature as seen from GOMOS/ENVISAT
ATMOSPHERIC CHEMISTRY AND PHYSICS 09/2010; 10:8873-8879. · 5.52 Impact Factor -
Article: GOMOS O$_3$, NO$_2$, and NO$_3$ observations in 2002-2008
Atmospheric Chemistry & Physics. 08/2010; 10:7723-7738. -
Article: Retrievals from GOMOS stellar occultation measurements using characterization of modeling errors
[show abstract] [hide abstract]
ABSTRACT: In this paper, we discuss the development of the inversion algorithm for the GOMOS (Global Ozone Monitoring by Occultation of Star) instrument on board the Envisat satellite. The proposed algorithm takes accurately into account the wavelength-dependent modeling errors, which are mainly due to the incomplete scintillation correction in the stratosphere. The special attention is paid to numerical efficiency of the algorithm. The developed method is tested on a large data set and its advantages are demonstrated. Its main advantage is a proper characterization of the uncertainties of the retrieved profiles of atmospheric constituents, which is of high importance for data assimilation, trend analyses and validation.Atmospheric Measurement Techniques Discussions. 01/2010; -
Article: Response of tropical stratospheric O<sub>3</sub>, NO<sub>2</sub> and NO<sub>3</sub> to the equatorial Quasi-Biennial Oscillation and to temperature as seen from GOMOS/ENVISAT
[show abstract] [hide abstract]
ABSTRACT: The stellar occultation spectrometer GOMOS (Global Ozone Monitoring by Occultation of Stars) on ESA's Envisat satellite measures vertical profiles O<sub>3</sub>, NO<sub>2</sub> and NO<sub>3</sub> 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 O<sub>3</sub>, NO<sub>2</sub> and NO<sub>3</sub> in the tropics. It is shown that the QBO of the equatorial wind induces variations in the local concentration larger than 10% for O<sub>3</sub> and larger than 25% for NO<sub>2</sub>. Quasi-Biennial Oscillation signals can be found in the evolution of the three constituents up to at least 45 km. We found that NO<sub>3</sub> is positively correlated with temperature up to 40 km in the region where it is in chemical equilibrium with O<sub>3</sub>. Above 40 km, NO<sub>3</sub> is no more in equilibrium during night and its concentration is correlated with both O<sub>3</sub> and NO<sub>2</sub>. For O<sub>3</sub> and NO<sub>2</sub>, our results confirm the existence of a transition from a dynamical control of O<sub>3</sub> below 28 km with O<sub>3</sub> correlated with NO<sub>2</sub> and temperature and a chemical/temperature control between 28 and 38 km with O<sub>3</sub> anti-correlated with NO<sub>2</sub> and temperature. Above 38 km and up to 50 km a regime never described before is found with both O<sub>3</sub> and NO<sub>2</sub> anti-correlated with temperature. For the NO<sub>2</sub>/temperature anti-correlation, our proposed explanation is the modulation of the N<sub>2</sub>O ascent in the upper stratosphere by the QBO and the modulation of the Brewer-Dobson circulation. The oxidation of N<sub>2</sub>O is the main source of NO<sub>y</sub> in this altitude region. An enhancement of the ascending motion will cool adiabatically the atmosphere and will increase the amount of N<sub>2</sub>O concentration available for NO<sub>y</sub> formation.Atmospheric Chemistry and Physics Discussions. 01/2010; -
Article: Global ozone monitoring by occultation of stars: an overview of GOMOS measurements on ENVISAT
[show abstract] [hide abstract]
ABSTRACT: GOMOS on ENVISAT (launched in February, 2002) is the first space instrument dedicated to the study of the atmosphere of the Earth by the technique of stellar occultations (Global Ozone Monitoring by Occultation of Stars). From a polar orbit, it allows to have a good latitude coverage. Because it is self-calibrated, it is particularly well adapted to the long time trend monitoring of stratospheric species. With 4 spectrometers the wavelength coverage of 248 nm to 942 nm allows to monitor ozone, H2O, NO2, NO3, air, aerosols, and O2. Two additional fast photometers (1 kHz sampling rate) allow for the correction of scintillations, as well as the study of the structure of air density irregularities, resulting from gravity waves and turbulence. A high vertical resolution profile of the temperature may also be obtained from the time delay between the red and the blue photometer. Noctilucent clouds (Polar Mesospheric Clouds, PMC), are routinely observed in both polar summers, and global observations of OCLO and sodium are achieved. The instrument configuration, dictated by the scientific objectives rationale and technical constraints, are described, together with the typical operations along one orbit, and statistics over 5 years of operation. Typical atmospheric transmission spectra are presented, and some retrieval difficulties are discussed, in particular for O2 and H2O. An overview of a number of scientific results is presented, already published or found in more details as companion papers in the same ACP GOMOS special issue. This paper is particularly intended to provide the incentive for GOMOS data exploitation, available to the whole scientific community in the ESA data archive, and to help the GOMOS data users to better understand the instrument, its capabilities and the quality of its measurements, for an optimized scientific return.Atmospheric Chemistry and Physics Discussions. 01/2010; -
Article: Retrieval of atmospheric parameters from GOMOS data
[show abstract] [hide abstract]
ABSTRACT: The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European Space Agency's ENVISAT satellite measures attenuation of stellar light in occultation geometry. Daytime measurements also record scattered solar light from the atmosphere. The wavelength regions are the ultraviolet-visible band 248–690 nm and two infrared bands at 755–774 nm and at 926–954 nm. From UV-Visible and IR spectra the vertical profiles of O3, NO2, NO3, H2O, O2 and aerosols can be retrieved. In addition there are two 1 kHz photometers at blue 473–527 nm and red 646–698 nm. Photometer data are used to correct spectrometer measurements for scintillations and to retrieve high resolution temperature profiles as well as gravity wave and turbulence parameters. Measurements cover altitude region 5–150 km. Atmospherically valid data are obtained in 15–100 km. In this paper we present an overview of the GOMOS retrieval algorithms for stellar occultation measurements. The low signal-to-noise ratio and the refractive effects due to the point source nature of stars have been important drivers in the development of GOMOS retrieval algorithms. We present first the Level 1b algorithms that are used to correct instrument related disturbances in the spectrometer and photometer measurements The Level 2 algorithms deal with the retrieval of vertical profiles of atmospheric gaseous constituents, aerosols and high resolution temperature. We divide the presentation into correction for refractive effects, high resolution temperature retrieval and spectral/vertical inversion. The paper also includes discussion about the GOMOS algorithm development, expected improvements, access to GOMOS data and alternative retrieval approaches.Atmospheric Chemistry and Physics Discussions. 01/2010; -
Article: GOMOS O<sub>3</sub>, NO<sub>2</sub>, and NO<sub>3</sub> observations in 2002–2008
[show abstract] [hide abstract]
ABSTRACT: The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument onboard the European Space Agency's ENVISAT satellite measures ozone, NO<sub>2</sub>, NO<sub>3</sub>, H<sub>2</sub>O, O<sub>2</sub>, and aerosols using the stellar occultation method. Global coverage, good vertical resolution and the self-calibrating measurement method make GOMOS observations a promising data set for building various climatologies and time series. In this paper we present GOMOS nighttime measurements of ozone, NO<sub>2</sub>, and NO<sub>3</sub> during six years 2002–2008. Using zonal averages we show the time evolution of the vertical profiles as a function of latitude. In order to get continuous coverage in time we restrict the latitudinal region to 50° S–50° N. Time development is analysed by fitting constant, annual and semi-annual terms as well as solar and QBO proxies to the daily time series. Ozone data cover the stratosphere, mesosphere and lower thermosphere (MLT). NO<sub>2</sub> and NO<sub>3</sub> data cover the stratosphere. In addition to detailed analysis of profiles we derive total column distributions using the fitted time series. The time-independent constant term is determined with a good accuracy (better than 1%) for all the three gases. The median retrieval accuracy for the annual and semi-annual term varies in the range 5–20%. For ozone the annual terms dominate in the stratosphere giving early winter ozone maxima at mid-latitudes. Above the ozone layer the annual terms change the phase which results in ozone summer maximum up to 80 km. In the MLT the annual terms dominate up to 80 km where the semiannual terms start to grow. In the equatorial MLT the semi-annual terms dominate the temporal evolution whereas in the mid-latitude MLT annual and semi-annual terms compete evenly. In the equatorial stratosphere the QBO dominates the time development but the solar term is too weak to be determined. In the MLT above 85 km the solar term grows significantly and ozone has 15–20% dependence on the solar cycle. For NO<sub>2</sub> below 32 km the annual summer maxima dominates at mid-latitudes whereas in the equatorial region a strong QBO prevails. In northern mid-latitudes a strong solar term appears in the upper stratosphere. For NO<sub>3</sub> the annual variation dominates giving rise to summer maxima. The NO<sub>3</sub> distribution is controlled by temperature and ozone.Atmospheric Chemistry and Physics. 01/2010; -
Article: Optical extinction by upper tropospheric/stratospheric aerosols and clouds: GOMOS observations for the period 2002–2008
[show abstract] [hide abstract]
ABSTRACT: Although the retrieval of aerosol extinction coefficients from satellite remote measurements is notoriously difficult (in comparison with gaseous species) due to the lack of typical spectral signatures, important information can be obtained. In this paper we present an overview of the current operational nighttime UV/Vis aerosol extinction profile results for the GOMOS star occultation instrument, spanning the period from August 2002 to May 2008. Some problems still remain, such as the ones associated with incomplete scintillation correction and the aerosol spectral law implementation, but good quality extinction values are obtained at a wavelength of 500 nm. Typical phenomena associated with atmospheric particulate matter in the Upper Troposphere/Lower Stratosphere (UTLS) are easily identified: Polar Stratospheric Clouds, tropical subvisual cirrus clouds, background stratospheric aerosols, and post-eruption volcanic aerosols (with their subsequent dispersion around the globe). For the first time, we show comparisons of GOMOS 500 nm particle extinction profiles with the ones of other satellite occultation instruments (SAGE II, SAGE III and POAM III), of which the good agreement lends credibility to the GOMOS data set. Yearly zonal statistics are presented for the entire period considered. Time series furthermore convincingly show an important new finding: the sensitivity of GOMOS to the sulfate input by moderate volcanic eruptions such as Manam (2005) and Soufrière Hills (2006). Finally, PSCs are well observed by GOMOS and a first qualitative analysis of the data agrees well with the theoretical PSC formation temperature. Therefore, the importance of the GOMOS aerosol/cloud extinction profile data set is clear: a long-term data record of PSCs, subvisual cirrus, and background and volcanic aerosols in the UTLS region, consisting of hundreds of thousands of altitude profiles with near-global coverage, with the potential to fill the aerosol/cloud extinction data gap left behind after the discontinuation of occultation instruments such as SAGE II, SAGE III and POAM III.ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2010; · 5.52 Impact Factor -
Article: Simultaneous measurements of OClO, NO$_2$ and O$_3$ in the Arctic polar vortex by the GOMOS instrument
ATMOSPHERIC CHEMISTRY AND PHYSICS 10/2009; 9:7857-7866. · 5.52 Impact Factor -
Article: Simultaneous measurements of OClO, NO<sub>2</sub> and O<sub>3</sub> in the Arctic polar vortex by the GOMOS instrument
[show abstract] [hide abstract]
ABSTRACT: We present the first nighttime measurements of OClO from a limb-viewing satellite instrument in the Arctic polar vortex. The relationship between OClO, NO<sub>2</sub> and O<sub>3</sub> slant column densities in the Arctic polar vortex are analyzed from the GOMOS measurements. The retrieval process is based on a differential optical absorption spectroscopy (DOAS) method applied on the weighted median GOMOS transmittances. A study of the longitudinal distributions of OClO, NO<sub>2</sub> and O<sub>3</sub> above 65° north in January 2008 is presented. It shows a strong halogen activation in the lower stratosphere and a strong denoxification in the entire stratosphere inside the Arctic polar vortex. Time series of temperatures and OClO, NO<sub>2</sub> and O<sub>3</sub> slant column densities for the winters 2002/2003 to 2007/2008 are also presented. They highlight the correlation between temperature, OClO and NO<sub>2</sub>. The GOMOS instrument appears to be a very suitable instrument for the monitoring of OClO, NO<sub>2</sub> and O<sub>3</sub> in the stratosphere during nighttime.Atmospheric Chemistry and Physics. 01/2009; -
Article: Global analysis of scintillation variance: Indication of gravity wave breaking in the polar winter upper stratosphere
[show abstract] [hide abstract]
ABSTRACT: [1] Stellar scintillations observed through the Earth atmosphere are caused by air density irregularities generated mainly by internal gravity waves and turbulence. We present global analysis of scintillation variance in two seasons of year 2003 based on GOMOS/Envisat fast photometer measurements. Scintillation variance can serve as a qualitative indicator of intensity of small-scale processes in the stratosphere. Strong increase of scintillation variance at high latitudes in winter is observed. The maximum of scintillation variance can be associated with the polar night jet. The simplified spectral analysis has shown the transition of scintillation spectra toward small scales with altitude, which is probably related with turbulence appearing as a result of wave breaking. The breaking of gravity waves in the polar night jet seems to start in the upper stratosphere, a predicted, but not confirmed by observations before, feature. Weaker enhancements in tropics are also observed; they might be related to tropical convection.Geophysical Research Letters 02/2007; 34:3812. · 3.79 Impact Factor -
Article: A 2003 stratospheric aerosol extinction and PSC climatology from GOMOS measurements on Envisat
[show abstract] [hide abstract]
ABSTRACT: Stratospheric aerosols play an important role in a number of atmospheric issues such as midlatitude ozone depletion, atmospheric dynamics and the Earth radiative budget. Polar stratospheric clouds on the other hand are a crucial factor in the yearly Arctic and Antarctic ozone depletion. It is therefore important to quantify the stratospheric aerosol/PSC abundance. In orbit since March 2002, the GOMOS instrument onboard the European Envisat satellite has provided a vast aerosol extinction data set. In this paper we present aerosol/PSC zonal median values that were constructed from this data set, together with a discussion of the results.ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2005; · 5.52 Impact Factor -
Conference Proceeding: The GOMOS processing chain and products
[show abstract] [hide abstract]
ABSTRACT: ESA's ENVISAT in year 2000 and will measure ozone with unprecedented long term accuracy and vertical resolution. GOMOS observes stellar occultations, and determines ozone, NO<sub>2</sub>, NO<sub>3 </sub>, aerosol, O<sub>2</sub>, H<sub>2</sub>O and possibly OClO concentrations from the ratio of two stellar spectra, one outside the atmosphere, one through the atmosphere. The first step of the processing, Level 1b, consists of various instrumental corrections to obtain the measured atmospheric spectral transmission as a function of altitude/geolocation. The second step (Level 2) consists of one spectral inversion for each line of sight (retrieval of integrated line densities of various constituents) and one vertical inversion for the whole occultation. The analysis of two fast photometers (1 kHz) data will produce a high resolution profile for the temperature profile. Higher data products will be constructed with the sequential assimilation of GOMOS data into a CTM modelGeoscience and Remote Sensing Symposium, 1999. IGARSS '99 Proceedings. IEEE 1999 International; 02/1999 -
Article: A global climatology of the mesospheric sodium layer from GOMOS data during the 2002–2008 period
[show abstract] [hide abstract]
ABSTRACT: This paper presents a climatology of the mesospheric sodium layer built from the processing of 7 years of GOMOS data. With respect to preliminary results already published for the year 2003, a more careful analysis was applied to the averaging of occultations inside the climatological bins (10° in latitude-1 month). Also, the slant path absorption lines of the Na doublet around 589 nm shows evidence of partial saturation that was responsible for an underestimation of the Na concentration in our previous results. The sodium climatology has been validated with respect to the Fort Collins lidar measurements and, to a lesser extent, to the OSIRIS 2003–2004 data. Despite the important natural sodium variability, we have shown that the Na vertical column has a marked semi-annual oscillation at low latitudes that merges into an annual oscillation in the polar regions, a spatial distribution pattern that was unreported so far. The sodium layer seems to be clearly influenced by the mesospheric global circulation and the altitude of the layer shows clear signs of subsidence during polar winter. The climatology has been parameterized by time-latitude robust fits to allow for easy use. Taking into account the non-linearity of the transmittance due to partial saturation, an experimental approach is proposed to derive mesospheric temperatures from limb remote sounding measurements.Atmospheric Chemistry and Physics. -
Article: GOMOS data characterization and error estimation
[show abstract] [hide abstract]
ABSTRACT: The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument uses stellar occultation technique for monitoring ozone and other trace gases in the stratosphere and mesosphere. The self-calibrating measurement principle of GOMOS together with a relatively simple data retrieval where only minimal use of a priori data is required, provides excellent possibilities for long term monitoring of atmospheric composition. GOMOS uses about 180 brightest stars as the light source. Depending on the individual spectral characteristics of the stars, the signal-to-noise ratio of GOMOS is changing from star to star, resulting also varying accuracy to the retrieved profiles. We present the overview of the GOMOS data characterization and error estimation, including modeling errors, for ozone, NO2, NO3 and aerosol profiles. The retrieval error (precision) of the night time measurements in the stratosphere is typically 0.5–4% for ozone, about 10–20% for NO2, 20–40% for NO3 and 2–50% for aerosols. Mesospheric O3, up to 100 km, can be measured with 2–10% precision. The main sources of the modeling error are the incompletely corrected atmospheric turbulence causing scintillation, inaccurate aerosol modeling, uncertainties in cross sections of the trace gases and in the atmospheric temperature. The sampling resolution of GOMOS varies depending on the measurement geometry. In the data inversion a Tikhonov-type regularization with pre-defined target resolution requirement is applied leading to 2–3 km resolution for ozone and 4 km resolution for other trace gases.Atmospheric Chemistry and Physics. -
Article: An Exploitation of Satellite-based Observation for Health Information: The UFOS Project
[show abstract] [hide abstract]
ABSTRACT: Short, medium and long-term trends of UV intensity levels are of crucial importance for either assessing effective biological impacts on human population, or implementing adequate preventive behaviours. Better information on a large spatial scale and increased public awareness of the short-term variations in UV values will help to support health agencies' goals of educating the public on UV risks. The Ultraviolet Forecast Operational Service Project (UFAS), financed in part by the European Commission/DG Information Society (TEN-TELECOM programme), aims to exploit satellite-based observations and to supply a set of UV products directly useful to health care. The short-term objective is to demonstrate the technical and economical feasibility and benefits that could be brought by such a system. UFOS is carried out by ACRI, with the support of an Advisory Group chaired by WHO and involving representation from the sectors of Health (WHO, INTERSUN collaborating centres, ZAMBON), Environment (WMO, IASB), and Telecommunications (EURECOM, IMET).
