Photoionization and photoabsorption cross sections of O, N2, O2, and N for aeronomic calculations

Fennelly, J. A.; Torr, D. G.

doi:10.1016/0092-640x(92)90004-2

Cited by 154 publications

(98 citation statements)

References 28 publications

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“…These use data obtained with the Millstone Hill radar, and so relate to individual occasions rather than the mean ionosphere used in the present work. In the most recent study (Buonsanto et al, 1995) plotted results show that use of the older ionisation cross-sections, instead of the more recent values from Fennelly and Torr (1992), gives an increase of about 8% in N K E. This compares well with the increase of 9% in Fig. 6.…”

Section: Electron Densitysupporting

confidence: 75%

“…To reproduce these changes correctly, and to include the secondary ionisation produced by high-energy photons in the range 25-50 A s , the normal band 1 is replaced by four bands covering 25-40, 40-60, 60-80 and 80-100 A s . Photoionisation cross-sections for these bands are obtained from the detailed data of Fenelly and Torr (1992), as described in Titheridge (1996).…”

Section: The Modelling Programmentioning

confidence: 99%

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Model results for the ionospheric E region: solar and seasonal changes

Titheridge

1997

Ann. Geophys.

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Abstract.A new, empirical model for NO densities is developed, to include physically reasonable variations with local time, season, latitude and solar cycle. Model calculations making full allowance for secondary production, and ionising radiations at wavelengths down to 25 A s , then give values for the peak density N K E that are only 6% below the empirical IRI values for summer conditions at solar minimum. At solar maximum the difference increases to 16%. Solar-cycle changes in the EUVAC radiation model seem insufficient to explain the observed changes in N K E, with any reasonable modifications to current atmospheric constants. Hinteregger radiations give the correct change, with results that are just 2% below the IRI values throughout the solar cycle, but give too little ionisation in the E-F valley region. To match the observed solar increase in N K E, the high-flux reference spectrum in the EUVAC model needs an overall increase of about 20% (or 33% if the change is confined to the less well defined radiations at (150 A s ). Observed values of N K E show a seasonal anomaly, at mid-latitudes, with densities about 10% higher in winter than in summer (for a constant solar zenith angle). Composition changes in the MSIS86 atmospheric model produce a summer-to-winter change in N K E of about !2% in the northern hemisphere, and #3% in the southern hemisphere. Seasonal changes in NO produce an additional increase of about 5% in winter, near solar minimum, to give an overall seasonal anomaly of 8% in the southern hemisphere. Near solar maximum, reported NO densities suggest a much smaller seasonal change that is insufficient to produce any winter increase in N K E. Other mechanisms, such as the effects of winds or electric fields, seem inadequate to explain the observed change in N K E. It therefore seems possible that current satellite data may underestimate the mean seasonal variation in NO near solar maximum. A not unreasonable change in the data, to give the same 2:1 variation as at solar minimum, can produce a seasonal

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Section: Electron Densitysupporting

confidence: 75%

Section: The Modelling Programmentioning

confidence: 99%

Model results for the ionospheric E region: solar and seasonal changes

Titheridge

1997

Ann. Geophys.

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“…The photoabsorption cross-sections for the dominant atomic components (O, N, He) were taken from Verner et al (1996) and Fennelly & Torr (1992), for O 2 and N 2 from Verner et al (1996) and Cole & Dexter (1978). A comparison has shown that in the spectral interval 5-35 nm the difference between the data from different sources does not exceed 2% for O and N and 10% for O 2 and N 2 which is close to the theoretical data accuracy (5-8%).…”

Section: Comparison Of Experimental Transmittancementioning

confidence: 68%

Validation of Earth atmosphere models using solar EUV observations from the CORONAS and PROBA2 satellites in occultation mode

Slemzin

Ulyanov

Gaikovich

et al. 2016

J. Space Weather Space Clim.

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Aims: Knowledge of properties of the Earth's upper atmosphere is important for predicting the lifetime of low-orbit spacecraft as well as for planning operation of space instruments whose data may be distorted by atmospheric effects. The accuracy of the models commonly used for simulating the structure of the atmosphere is limited by the scarcity of the observations they are based on, so improvement of these models requires validation under different atmospheric conditions. Measurements of the absorption of the solar extreme ultraviolet (EUV) radiation in the upper atmosphere below 500 km by instruments operating on low-Earth orbits (LEO) satellites provide efficient means for such validation as well as for continuous monitoring of the upper atmosphere and for studying its response to the solar and geomagnetic activity. Method: This paper presents results of measurements of the solar EUV radiation in the 17 nm wavelength band made with the SPIRIT and TESIS telescopes on board the CORONAS satellites and the SWAP telescope on board the PROBA2 satellite in the occulted parts of the satellite orbits. The transmittance profiles of the atmosphere at altitudes between 150 and 500 km were derived from different phases of solar activity during solar cycles 23 and 24 in the quiet state of the magnetosphere and during the development of a geomagnetic storm. We developed a mathematical procedure based on the Tikhonov regularization method for solution of ill-posed problems in order to retrieve extinction coefficients from the transmittance profiles. The transmittance profiles derived from the data and the retrieved extinction coefficients are compared with simulations carried out with the NRLMSISE-00 atmosphere model maintained by Naval Research Laboratory (USA) and the DTM-2013 model developed at CNES in the framework of the FP7 project ATMOP. Results: Under quiet and slightly disturbed magnetospheric conditions during high and low solar activity the extinction coefficients calculated by both models agreed with the measurements within the data errors. The NRLMSISE-00 model was not able to predict the enhancement of extinction above 300 km observed after 14 h from the beginning of a geomagnetic storm whereas the DTM-2013 model described this variation with good accuracy.

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“…We tested several more recent models, but in the energy range relevant in this paper, we did not ®nd signi®cant di erences. The cross section set is from Fennelly and Torr (1992). The two sharp peaks in the suprathermal angular velocity distribution function, seen in the top panel of Fig.…”

Section: Intensity Analysismentioning

confidence: 99%

Effect of suprathermal electrons on the intensity and Doppler frequency of electron plasma lines

Guio

Lilensten

1999

Ann. Geophys.

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Abstract. In an incoherent scattering radar experiment, the spectral measurement of the so-called up-and downshifted electron plasma lines provides information about their intensity and their Doppler frequency. These two spectral lines correspond, in the backscatter geometry, to two Langmuir waves travelling towards and away from the radar. In the daytime ionosphere, the presence of a small percentage of photoelectrons produced by the solar EUV of the total electron population can excite or damp these Langmuir waves above the thermal equilibrium, resulting in an enhancement of the intensity of the lines above the thermal level. The presence of photo-electrons also modi®es the dielectric response function of the plasma from the Maxwellian and thus in¯uences the Doppler frequency of the plasma lines. In this paper, we present a high time-resolution plasma-line data set collected on the EISCAT VHF radar. The analysed data are compared with a model that includes the e ect of a suprathermal electron population calculated by a transport code. By comparing the intensity of the analysed plasma lines data to our model, we show that two sharp peaks in the electron suprathermal distribution in the energy range 20±30 eV causes an increased Landau damping around 24.25 eV and 26.25 eV. We have identi®ed these two sharp peaks as the e ect of the photoionisation of N 2 and O by the intense¯ux of monochromatic HeII radiation of wavelength 30.378 nm (40.812 eV) created in the chromospheric network and coronal holes. Furthermore, we see that what would have been interpreted as a mean Doppler drift velocity for a Maxwellian plasma is actually a shift of the Doppler frequency of the plasma lines due to suprathermal electrons.

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Photoionization and photoabsorption cross sections of O, N2, O2, and N for aeronomic calculations

Cited by 154 publications

References 28 publications

Model results for the ionospheric E region: solar and seasonal changes

Model results for the ionospheric E region: solar and seasonal changes

Validation of Earth atmosphere models using solar EUV observations from the CORONAS and PROBA2 satellites in occultation mode

Effect of suprathermal electrons on the intensity and Doppler frequency of electron plasma lines

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