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Search Results: 1 - 10 of 258575 matches for " V. F. Sofieva "
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Anisotropy of small-scale stratospheric irregularities retrieved from scintillations of a double star α-Cru observed by GOMOS/ENVISAT
V. Kan, V. F. Sofieva,F. Dalaudier
Atmospheric Measurement Techniques (AMT) & Discussions (AMTD) , 2012,
Abstract: In this paper, we discuss estimating anisotropy of air density irregularities (ratio of characteristic horizontal and vertical scales) from satellite observations of bi-chromatic scintillations of a double star whose components are not resolved by the detector. The analysis is based on fitting experimental auto- and cross-spectra of scintillations by those computed using the 3-D spectral model of atmospheric irregularities consisting of anisotropic and isotropic components. Application of the developed method to the scintillation measurements of the double star α-Cru by GOMOS (Global Ozone Monitoring by Occultation of Stars) fast photometers results in estimates of anisotropy coefficient of ~15–20 at altitudes 30–38 km, as well as other parameters of atmospheric irregularities. The obtained estimates of the anisotropy coefficient correspond to small-scale irregularities, close to the buoyancy scale.
Anisotropy of small-scale stratospheric irregularities retrieved from scintillations of a double star α-Cru observed by GOMOS/ENVISAT
V. Kan,V. F. Sofieva,F. Dalaudier
Atmospheric Measurement Techniques Discussions , 2012, DOI: 10.5194/amtd-5-4881-2012
Abstract: In this paper, we discuss estimating anisotropy of air density irregularities (ratio of characteristic horizontal and vertical scales) from satellite observations of bi-chromatic scintillations of a double star whose components are not resolved by the detector. The analysis is based on fitting experimental auto- and cross-spectra of scintillations by those computed using the 3-D spectral model of atmospheric irregularities consisting of anisotropic and isotropic components. Application of the developed method to the scintillation measurements of the double star α-Cru by GOMOS (Global Ozone Monitoring by Occultation of Stars) fast photometers results in estimates of anisotropy coefficient of ~15–20 at altitudes 30–38 km, as well as other parameters of atmospheric irregularities. The obtained estimates of the anisotropy coefficient correspond to small-scale irregularities, close to the buoyancy scale.
Technical Note: Scintillations of the double star α Cru observed by GOMOS/Envisat
V. F. Sofieva,F. Dalaudier,V. Kan,A. S. Gurvich
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: In this paper, we discuss scintillation time-spectra of the double star α Cru, which were measured by the GOMOS/Envisat photometer. The components of α Cru are not resolved by the angular field of view of the detector. The double structure of the light source reveals itself in the modulation of the observed scintillation spectra; this modulation is caused by anisotropic irregularities of stratospheric air density. We present qualitative and quantitative explanation of properties of the double-star scintillation spectra. Possibilities of using double star scintillations for studying atmospheric air density irregularities are also discussed in the paper.
Influence of scintillation on GOMOS ozone retrievals
V. F. Sofieva,V. Kan,F. Dalaudier,E. Kyr?l?
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: The stellar light passed through the Earth atmosphere is affected by refractive effects, which should be taken into account in retrievals from stellar occultation measurements. Scintillation caused by air density irregularities is a nuisance for retrievals of atmospheric composition. In this paper, we consider the influence of scintillation on stellar occultation measurements and on quality of ozone retrievals from these measurements, based on experience of the GOMOS (Global Ozone Monitoring by Occultation of Stars) instrument on board the Envisat satellite. In the GOMOS retrievals, the scintillation effect is corrected using scintillation measurements by the fast photometer. We present quantitative estimates of the current scintillation correction quality and of the impact of scintillation on ozone retrievals by GOMOS. The analysis has shown that the present scintillation correction efficiently removes the distortion of transmission spectra caused by anisotropic scintillations. The impact of errors of dilution and anisotropic scintillation correction on quality of ozone retrievals is negligible. However, the current scintillation correction is not able to remove the wavelength-dependent distortion of transmission spectra caused by isotropic scintillations, which can be present in off-orbital-plane occultations. This distortion may result in error of ozone retrievals of 0.5–1.5% at altitudes 20–40 km. This contribution to the error budget is significant for bright stars. The advanced inversion methods that can minimize the influence of scintillation correction error are also discussed.
Influence of scintillation on quality of ozone monitoring by GOMOS
V. F. Sofieva,V. Kan,F. Dalaudier,E. Kyr?l?
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: Stellar light passing through the Earth atmosphere is affected by refractive effects, which should be taken into account in retrievals from stellar occultation measurements. Scintillation caused by air density irregularities is a nuisance for retrievals of atmospheric composition. In this paper, we consider the influence of scintillation on stellar occultation measurements and on the quality of ozone retrievals from these measurements, based on experience of the GOMOS (Global Ozone Monitoring by Occultation of Stars) instrument on board the Envisat satellite. In GOMOS retrievals, the scintillation effect is corrected using scintillation measurements by the fast photometer. We present quantitative estimates of the current scintillation correction quality and of the impact of scintillation on ozone retrievals by GOMOS. The analysis has shown that the present scintillation correction efficiently removes the distortion of transmission spectra caused by scintillations, which are generated by anisotropic irregularities of air density. The impact of errors of dilution and anisotropic scintillation correction on the quality of ozone retrievals is negligible. However, the current scintillation correction is not able to remove the wavelength-dependent distortion of transmission spectra caused by isotropic scintillations, which can be present in off-orbital-plane occultations. This distortion may result in ozone retrieval errors of 0.5–1.5% at altitudes 20–40 km. This contribution constitutes a significant percentage of the total error for bright stars. The advanced inversion methods that can minimize the influence of scintillation correction error are also discussed.
Technical note: Scintillations of the double star α Cru observed by GOMOS/Envisat
V. F. Sofieva,F. Dalaudier,V. Kan,A. S. Gurvich
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: In this paper, we discuss scintillation time-spectra of the double star α Cru, which were measured by the GOMOS/Envisat photometer. The components of α Cru are not resolved by the angular field of view of the detector. The double structure of the light source reveals itself in the modulation of the observed scintillation spectra; this modulation is caused by anisotropic irregularities of the stratospheric air density. We present a qualitative and quantitative explanation of the properties of the double-star scintillation spectra. Possibilities of using double star scintillations for studying atmospheric air density irregularities are also discussed in the paper.
An alternative explanation of PMSE-like scatter in MF radar data
V. F. Sofieva, E. Kyr ,E. Kyr l
Annales Geophysicae (ANGEO) , 2004,
Abstract: This paper discusses the smoothness of vertical profiles of ozone concentrations. We describe the smoothness of ozone profiles via a characteristic scale of the profile fluctuations. The characteristic scale was computed for 11-years (1989-1999) ozone sonde data at Sodankyl . Mean values of the characteristic scale were determined. They are ~1km in the troposphere and ~1.4km in the lower stratosphere (up to 25km). Only slight seasonal variations of these parameters are observed. The information about smoothness of ozone profiles is needed both in the instrumental design for defining the vertical resolution requirements and in the development of inversion algorithms from remote sensing measurements, in order to obtain the best accuracy in retrieved ozone profiles and sufficient resolution. Full Article (PDF, 2675 KB) Citation: Sofieva, V. F., Kyr , E., and Kyr l , E.: Smoothness of ozone profiles: analysis of 11 years of ozone sonde measurements at Sodankyl , Ann. Geophys., 22, 2723-2727, doi:10.5194/angeo-22-2723-2004, 2004. Bibtex EndNote Reference Manager XML
Retrievals from GOMOS stellar occultation measurements using characterization of modeling errors
V. F. Sofieva,J. Vira,E. Kyr?l?,J. Tamminen
Atmospheric Measurement Techniques Discussions , 2010,
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.
Ozone profile smoothness as a priori information in the inversion of limb measurements
V. F. Sofieva, J. Tamminen, H. Haario, E. Kyr l ,M. Lehtinen
Annales Geophysicae (ANGEO) , 2004,
Abstract: In this work we discuss inclusion of a priori information about the smoothness of atmospheric profiles in inversion algorithms. The smoothness requirement can be formulated in the form of Tikhonov-type regularization, where the smoothness of atmospheric profiles is considered as a constraint or in the form of Bayesian optimal estimation (maximum a posteriori method, MAP), where the smoothness of profiles can be included as a priori information. We develop further two recently proposed retrieval methods. One of them - Tikhonov-type regularization according to the target resolution - develops the classical Tikhonov regularization. The second method - maximum a posteriori method with smoothness a priori - effectively combines the ideas of the classical MAP method and Tikhonov-type regularization. We discuss a grid-independent formulation for the proposed inversion methods, thus isolating the choice of calculation grid from the question of how strong the smoothing should be. The discussed approaches are applied to the problem of ozone profile retrieval from stellar occultation measurements by the GOMOS instrument on board the Envisat satellite. Realistic simulations for the typical measurement conditions with smoothness a priori information created from 10-years analysis of ozone sounding at Sodankyl and analysis of the total retrieval error illustrate the advantages of the proposed methods. The proposed methods are equally applicable to other profile retrieval problems from remote sensing measurements. Full Article (PDF, 286 KB) Citation: Sofieva, V. F., Tamminen, J., Haario, H., Kyr l , E., and Lehtinen, M.: Ozone profile smoothness as a priori information in the inversion of limb measurements, Ann. Geophys., 22, 3411-3420, doi:10.5194/angeo-22-3411-2004, 2004. Bibtex EndNote Reference Manager XML
Spatio-temporal observations of tertiary ozone maximum
V. F. Sofieva,E. Kyr?l?,P. T. Verronen,A. Sepp?l?
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: We present spatio-temporal distributions of tertiary ozone maximum (TOM), based on GOMOS (Global Ozone Monitoring by Occultation of Stars) ozone measurements in 2002–2006. The tertiary ozone maximum is typically observed in the high-latitude winter mesosphere at altitude ~72 km. Although the explanation for this phenomenon has been found recently – low concentrations of odd-hydrogen cause the subsequent decrease in odd-oxygen losses – models have had significant deviations from existing observations until recently. Good coverage of polar night regions by GOMOS data has allowed for the first time obtaining spatial and temporal observational distributions of night-time ozone mixing ratio in the mesosphere. The distributions obtained from GOMOS data have specific features, which are variable from year to year. In particular, due to a long lifetime of ozone in polar night conditions, the downward transport of polar air by the meridional circulation is clearly observed in the tertiary ozone maximum time series. Although the maximum tertiary ozone mixing ratio is achieved close to the polar night terminator (as predicted by the theory), TOM can be observed also at very high latitudes, not only in the beginning and at the end, but also in the middle of winter. We have compared the observational spatio-temporal distributions of tertiary ozone maximum with that obtained using WACCM (Whole Atmosphere Community Climate Model) and found that the specific features are reproduced satisfactorily by the model. Since ozone in the mesosphere is very sensitive to HOx concentrations, energetic particle precipitation can significantly modify the shape of the ozone profiles. In particular, GOMOS observations have shown that the tertiary ozone maximum was temporarily destroyed during the January 2005 and December 2006 solar proton events as a result of the HOx enhancement from the increased ionization.
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