On the variability of Lyman-alpha with solar activity

Bossy, L.; Nicolet, M.

doi:10.1016/0032-0633(81)90080-5

Cited by 50 publications

(6 citation statements)

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“…Absorption cross sections and ionization cross sections are based on Richards et al . [] and Banks and Kockarts [] for X‐ray energies and Bossy and Nicolet [] for Lyman Alpha. The auroral region ionization is generated from the characteristic energy and energy flux of the Hardy electron precipitation model [ Hardy et al ., ].…”

Section: Instrumentation and Modelsmentioning

confidence: 99%

Ionospheric model‐observation comparisons: E layer at Arecibo Incorporation of SDO‐EVE solar irradiances

et al. 2014

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This study evaluates how the new irradiance observations from the NASA Solar Dynamics Observatory (SDO) Extreme Ultraviolet Variability Experiment (EVE) can, with its high spectral resolution and 10 s cadence, improve the modeling of the E region. To demonstrate this a campaign combining EVE observations with that of the NSF Arecibo incoherent scatter radar (ISR) was conducted. The ISR provides E region electron density observations with high-altitude resolution, 300 m, and absolute densities using the plasma line technique. Two independent ionospheric models were used, the Utah State University Time-Dependent Ionospheric Model (TDIM) and Space Environment Corporation's Data-Driven D Region (DDDR) model. Each used the same EVE irradiance spectrum binned at 1 nm resolution from 0.1 to 106 nm. At the E region peak the modeled TDIM density is 20% lower and that of the DDDR is 6% higher than observed. These differences could correspond to a 36% lower (TDIM) and 12% higher (DDDR) production rate if the differences were entirely attributed to the solar irradiance source. The detailed profile shapes that included the E region altitude and that of the valley region were only qualitatively similar to observations. Differences on the order of a neutral-scale height were present. Neither model captured a distinct dawn to dusk tilt in the E region peak altitude. A model sensitivity study demonstrated how future improved spectral resolution of the 0.1 to 7 nm irradiance could account for some of these model shortcomings although other relevant processes are also poorly modeled.

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Section: Instrumentation and Modelsmentioning

confidence: 99%

Ionospheric model‐observation comparisons: E layer at Arecibo Incorporation of SDO‐EVE solar irradiances

et al. 2014

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“…The AE-E data studied were also studied by Hedin [1984] in relation to F10 and thermospheric density and temperature. Bossy and Nicolet [1981], Bossy [1983], and Oster [1983b] have criticized the AE-E measurements as suffering from shifts in the instrument sensitivity to EUV radiation, especially the H Lyman alpha measurements, and have suggested revisions be made to the AE-E data based on comparisons with F10. Because of the controversial nature of the long-term changes in the AE-E H Lyman alpha measurements we have included those data only for discussing some of their short-term variations.…”

Section: For the Ae-e Data File Sc# 2lobsmentioning

confidence: 99%

Temporal variations of solar EUV, UV, and 10,830‐Å radiations

Donnelly¹,

Hinteregger²,

Heath³

1986

J. Geophys. Res.

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The temporal characteristics of the full-disk chromospheric EUV fluxes agree well with those of the ground-based'measurements of the chromospheric He I absorption line at 10,830 A and differ systematically from those of the coronal EUV and 10.7-cm flux. The ratio of the flux increase during the rise of solar cycle 21 to that during solar rotation variations is uniformly high for the chromospheric EUV and corroborating 10,830-/!/fluxes, highest for the transition region and'"cool" coronal EUV fluxes (T < 2 x 106 øK), and lowest for the "hot" coronal EUV and 10.7-em flux. The rise and decay rates of episodes of major activity progress from those for the hot coronal EUV lines and the 10.7-cm flux to slower values for the chromospheric H Lyman alpha line, 10,830-A line, and photospheric 2050-/!• UV flux. We suggest that active region remnants contribute significantly to the solar cycle increase and during the decay of episodes of major activity. The ratio of power in 13-day periodicity to that for 27 days is high (1/3) for the photospheric UV flux, medium (1/6) for the chromospheric EUV and 10,830-A fluxes, and small to negligible for the hot coronal EUV fluxes. These ratios are used to estimate the dependence of active region emission on the solar central meridian distance for chromospheric and coronal EUV fluxes. SOLAR UV AND EUV RADIATION The solar UV full-disk flux at 2050 A, measured by the NIMBUS 7 satellite, was shown by Donnelly et al. [1985] to vary in close agreement with ground-based measurements of the He I absorption line at 10,830/•. These variations included the following three time scales: (1) short-term variations with quasi-periodicity of about 13.5 or 27.5 days that are caused by solar rotation of active region plages, (2) intermediate-term enhancements of several months caused by episodes of major activity, and (3) long-term solar cycle variations. These UV variations were also shown to differ from those of the 10.7-cm solar radio flux (F10) during episodes of major activity and when the 13.5-day periodicity was strong in the UV flux [Donnelly et al., 1983]. This paper extends the research of UV and 10,830-• temporal characteristics by including comparisons with the solar extreme ultraviolet (EUV) flux measurements from the AE-E satellite. The remainder of this section introduces the data studied and our general knowledge of solar UV and EUV radiations, including their terrestrial importance, spectral differences, magnitudes of variations, and solar source regions. The next section describes the AE-E data studied. Then the temporal characteristics and comparisons of the EUV, UV, and 10,830-/• measurements for short-, intermediate-, and long-term variations are presented. Next, the implications of the 13-day periodicity on the dependence of active region radiation on the region's central meridian distance (CMD) are discussed for chromospheric and coronal EUV lines. Finally, the relation of our results to the temporal characteristics of ground-based measures of solar This paper is not subject to U.S...

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“…Use of ground-based solar observations as a surrogate for UV irradiances has been extensive and varied. Attempts have been made to "correct" those UV observations which appear to have been affected by changes in instrument responsivity by using the 10.7-cm flux[Bossy and Nicolet, 1981] and the 10.7-cm flux [Hu•thes and Kesteven, 1981] have revealed the nonstationary, highly irregular and complex nature of solar variability; no completely satisfactory explanation of the variance observed in the ground-based solar variability records yet exists[Bray and Loughhead, 1964;Bloomfield, 1976]. It is evident inFigure 7, for example, that no two 11-year cycles within any one of these time series are identical.…”

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confidence: 99%

Solar ultraviolet irradiance variations: A review

Lean¹

1987

J. Geophys. Res.

280

132

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Despite the geophysical importance of solar ultraviolet radiation, specific aspects of its temporal variations have not yet been adequately determined experimentally, nor are the mechanisms for the variability completely understood. Satellite observations have verified the reality of solar ultraviolet irradiance variations over time scales of days and months, and model calculations have confirmed the association of these short‐term variations with the evolution and rotation of regions of enhanced magnetic activity on the solar disc. However, neither rocket nor satellite measurements have yet been made with sufficient accuracy and regularity to establish unequivocally the nature of the variability over the longer time of the 11‐year solar cycle. The comparative importance for the long‐term variations of local regions of enhanced magnetic activity and global scale activity perturbations is still being investigated. Solar ultraviolet irradiance variations over both short and long time scales are reviewed, with emphasis on their connection to solar magnetic activity. Correlations with ground‐based measures of solar variability are examined because of the importance of the ground‐based observations as historical proxies of ultraviolet irradiance variations. Current problems in understanding solar ultraviolet irradiance variations are discussed, and the measurements planned for solar cycle 22, which may resolve these problems, are briefly described.

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On the variability of Lyman-alpha with solar activity

Cited by 50 publications

References 8 publications

Ionospheric model‐observation comparisons: E layer at Arecibo Incorporation of SDO‐EVE solar irradiances

Ionospheric model‐observation comparisons: E layer at Arecibo Incorporation of SDO‐EVE solar irradiances

Temporal variations of solar EUV, UV, and 10,830‐Å radiations

Solar ultraviolet irradiance variations: A review

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