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Sökning: WFRF:(Axelsson T) > Teknik

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1.
  • Axelsson, Katarina, et al. (författare)
  • A study on the possibility to deduce the 2D distribution of the auroral electron precipitation from multi wavelength optical measurements with auroral imagers
  • 2011
  • Ingår i: Óptica Pura y Aplicada. - 0030-3917 .- 2171-8814. ; 44:4, s. 605-609
  • Tidskriftsartikel (refereegranskat)abstract
    • The intensity ratios of auroral emissions at different wavelengths are widely used for reconstruction of auroral electron parameters. This method works quite well if the measurements of the auroral emissions are conducted in the magnetic zenith direction. In this study we want to investigate the possibility to use the intensity ratio method in the case where the observations are made in a direction not parallel to the magnetic field. In particular, we want to check the possibility of using auroral data for deducing the 2D distribution of the auroral electron precipitation. We use ALIS multi-station measurements of the auroral red and green line emissions (6300 Å and 5577 Å) to get data in zenith and non-zenith directions. We also take into account that the red line emission peak and the green line emission peak are at different altitudes. The results of this investigation show we can obtain reliable results for angles up to 35º away from magnetic zenith.
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2.
  • Axelsson, Katarina, et al. (författare)
  • First negative system of N2 + in aurora : Simultaneous space-borne and ground-based measurements and modeling results
  • 2014
  • Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 32:5, s. 499-506
  • Tidskriftsartikel (refereegranskat)abstract
    • The auroral emission of the first negative system of N2 + at 427.8 nm is analyzed using simultaneous measurements from the ground with ALIS (Auroral Large Imaging System) and from space with optical (MAC) and particle (ESA) instruments of the Reimei satellite. The study has two main objectives. The first is validation of the absolute calibration of the ALIS and the Reimei MAC cameras. The other task is to evaluate different cross sections of the electron excitation of N2 + that are used for the modeling of the auroral 1N system emissions. The simultaneous measurements of the 427.8 nm emission by ALIS and Reimei imagers show excellent agreement, indicating that the calibration of the two instruments is correct. Comparison of the 427.8 nm emission intensity calculated using the incident electron flux measured by the Reimei particle instruments with intensities measured by the optical imagers show that the best match is reached with the cross section from Shemansky and Liu (2005).
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3.
  • Axelsson, Katarina, et al. (författare)
  • Spatial characteristics of wave-like structures in diffuse aurora obtained using optical observations
  • 2012
  • Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 30:12, s. 1693-1701
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the results of a statistical study using optical images from ALIS (Auroral Large Imaging System) to investigate the spatial and temporal variations of structures in diffuse aurora. Analysis of conjugate Reimei data shows that such fine structures are a result of modulation of high-energy precipitating electrons. Pitch angle diffusion into the loss cone due to interaction of whistler mode waves with plasma sheet electrons is the most feasible mechanism leading to high-energy electron precipitation. This suggests that the fine structure is an indication of modulations of the efficiency of the wave-particle interaction. The scale sizes and variations of these structures, mapped to the magnetosphere, can give us information about the characteristics of the modulating wave activity. We found the scale size of the auroral stripes and the spacing between them to be on average 13-14 km, which corresponds to 3-4 ion gyro radii for protons with an energy of 7 keV. The structures move southward with a speed close to zero in the plasma convection frame.
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4.
  • Brändström, U., et al. (författare)
  • Results from the intercalibration of optical low light calibration sources 2011
  • 2012
  • Ingår i: Geoscientific Instrumentation, Methods and Data Systems. - : Copernicus GmbH. - 2193-0856 .- 2193-0864. ; 1:1, s. 43-51
  • Tidskriftsartikel (refereegranskat)abstract
    • Following the 38th Annual European Meeting onAtmospheric Studies by Optical Methods in Siuntio in Finland,an intercalibration workshop for optical low light calibrationsources was held in Sodankyl¨a, Finland. The mainpurpose of this workshop was to provide a comparable scalefor absolute measurements of aurora and airglow. All sourcesbrought to the intercalibration workshop were compared tothe Fritz Peak reference source using the Lindau CalibrationPhotometer built by Wilhelm Barke and Hans Lauche in1984. The results were compared to several earlier intercalibrationworkshops. It was found that most sources were fairlystable over time, with errors in the range of 5–25 %. To furthervalidate the results, two sources were also intercalibratedat UNIS, Longyearbyen, Svalbard. Preliminary analysis indicatesagreement with the intercalibration in Sodankyl¨a withinabout 15–25 %.
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  • Resultat 1-5 av 5

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