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  • 1
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    Modelling Solar Spectral Irradiance Variations at Ultraviolet Wavelengths (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-11
    Description: Solar UV irradiance variations with solar activity are examined using a three component model of the CaII K chromospheric emission. This model, developed from ground based observations of the location, area and relative intensity of CaII K plage, in conjunction with measurements throughout solar cycle 21 of the full disc CaII K emission, includes the contributions to the ultraviolet flux from both plage and active network emission. The model successfully replicates changes in the Lyman alpha flux related to the 27 day rotation of solar plage, outbreaks (or rounds) of activity over periods of a year or more, and the growth and accumulation of active regions over the eleven year solar activity cycles. Estimates of the magnitude of the solar cycle variability of the UV emission between 200 and 300 nm are presented but cannot currently be verified by available observations.
    Keywords: SOLAR PHYSICS
    Type: NASA, Washington Solar Irradiance Variations on Active Region Time Scales; p 253-288
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  • 2
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    A three-component model of the variability of the solar ultraviolet flux 145-200 nM (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The variability of the ultraviolet flux between 145 and 200 nm over both the eleven-year cycle and the 27-day solar rotation period is examined in terms of chromospheric activity, as determined from ground-based observations of the CaII K chromosphere. A three-component model of the solar UV flux is developed which includes the contributions to the full disk flux from both plage and active network emission. Solar cycle and solar rotation variations derived from the model are compared with the results of satellite and rocket experiments and with the two-component model of Cook et al (1980). Finally, possible ways of improving the model are discussed.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research; 87; Dec. 1
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  • 3
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    Observed variability in the Fraunhofer line spectrum of solar flux, 1975 - 1980 (1981)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Over the five years double-pass spectrometer observations of the Sun-as-a-star revealed significant changes in line intensities. The photospheric component weakened linearly with time 0 to 2.3%. From a lack of correlation between these line weakenings and solar activity indicators like sunspots and plage, a global variation of surface properties is inferred. Model-atmosphere analysis suggests a slight reduction in the lower-photospheric temperature gradient corresponding to a 15% increase in the mixing length within the granulation layer. Chromospheric lines such as Ca II H and K, Ca II 8543 and the CN band head weaken synchronously with solar activity. Thus, the behavior of photospheric and chromospheric lines is markedly different, with the possibility of secular change for the former.
    Keywords: SOLAR PHYSICS
    Type: NASA. Goddard Space Flight Center Variations of the Solar Constant; p 95-109
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  • 4
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    Photoelectric observations of propagating sunspot oscillations (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Repeated intensity and velocity images of a large, isolated sunspot in both the chromospheric Ca II 8542 A and photospheric Fe I 5576 line were performed. It is shown by means of a movie of the digital data for the chromospheric line that a relationship exists between the propagating umbral disturbances and the running penumbral waves. Power spectra of the oscillations show a sharp peak at a period of about 170 sec in both the velocity and intensity signals, and the oscillations at any point in the sunspot are found to be very regular. The phase relationship between the velocity and the intensity of the chromospheric oscillations contrasts with that for the quiet sun. The mechanical energy flux carried by the observed umbral disturbances does not appear to be a significant contributor to the overall energy budget of the sunspot or the surrounding active region.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 253
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  • 5
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    The vertical propagation of waves in the solar atmosphere. II Phase delays in the quiet chromosphere and cell-network distinctions (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The differences in the phase of the velocity oscillations between a pair of chromospheric Ca II lines was measured using the Vacuum Tower Telescope at the Sacramento Peak Observatory. The observed phase differences indicate that the acoustic modes are trapped or envanescent, rather than propagating, in the chromosphere. Systematic distinctions are found in the phase delays between quiet network and cell interior regions for both intensity and velocity oscillations in photospheric and chromospheric lines. The theory of linear perturbations in an isothermal atmosphere is invoked to interpret these differences. From this analysis it is found that one or more of the following explanations is possible: (1) the radiative damping is more effective in the network than in the cell interior; (2) the network features exclude oscillations of large horizontal wavenumber; or (3) the scale height of the chromosphere is larger in the network than in the cell interior.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 253
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  • 6
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    Impulsive EUV bursts observed in C IV with OSO-8 (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Time sequences of profiles of the 1548 A line of C IV containing 51 EUV bursts observed in or near active regions are analyzed to determine the brightness, Doppler shift and line broadening characteristics of the bursts. The bursts have mean lifetimes of approximately 150 s, and mean increases in brightness at burst maximum of four-fold as observed with a field of view of 2 x 20 arc sec. Mean burst diameters are estimated to be 3 arc sec, or smaller. All but three of the bursts show Doppler shifts with velocities sometimes exceeding 75 km/s; 31 are dominated by red shifts and 17 are dominated by blue shifts. Approximately half of the latter group have red-shifted precursors. The bursts are interpreted as prominence material, such as surges and coronal rain, moving through the field of view of the spectrometer.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 66; June 198
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  • 7
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    Accretion disk coronae (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Recent observations of partial X-ray eclipses from 4U1822-37 have shown that the central X-ray source in this system is diffused by a large Compton-thick accretion disk corona (ADC). Another binary, 4U2129-47, also displays a partial eclipse and contains an ADC. The possible origin of an ADC is discussed and a simple hydrostatic evaporated ADC model is developed which, when applied to 4U1822-37, 4U2129+47 and Cyg X-3, can explain their temporal and spectral properties. The quasi-sinusoidal modulation of all three sources can be reconciled with the partial occultation of the ADC by a bulge at the edge of the accretion disk which is caused by the inflowing material. The height of this bulge is an order of magnitude larger than the hydrostatic disk height and is the result of turbulence in the outer region of the disk. The spectral properties of all three sources can be understood in terms of Compton scattering of the original source spectrum by the ADC. Spectral variations with epoch in Cyg X-3 are probably caused by changes in the optical depth of the corona. A consequence of our model is that any accreting neutron star X-ray source in a semi-detached binary system which is close to its Eddington limit most likely contains an optically thick ADC.
    Keywords: SOLAR PHYSICS
    Type: NASA-TM-83840
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