Ionization rates due to the attenuation of 1‐100 Å nonflare solar X rays in the terrestrial atmosphere

Flare-associated soft X-ray bursts (8–12 A) are examined for 283 events observed by OSO-III These bursts are shown to be predominantly thermal in nature Their time-profiles are roughly similar to those of the associated Hα flares, although the X-ray burst begins about two minutes earlier, on the average The strength of the soft X-ray burst is directly related to the area and brilliance of the flare, the age and ‘flare-richness’ of the associated plage, and the general level of solar activity at the time of the burst The peak enhancements in the soft X-ray and Hα emission rates during flares are of the same order of magnitude, as are the total flare energies radiated at these wavelengths We estimate that soft X-radiation accounts for up to 10% of a flare's total electromagnetic emission

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Solar soft x rays and solar activity. ii. soft x ray emission during solar flares.

The coronal spectrum provides a unique opportunity to probe atomic processes in a high temperature plasma. The corona is optically thin, at low density, and the coronal ions are highly stripped. These characteristics result in an emission line spectrum with a rich multiplet structure, with forbidden lines prominent in the spectrum, and deexcitation of metastable states by two photon decay making significant contributions to the continuum. The multiplet structure is further complicated by the presence of satellite lines from autoionizing states formed during recombination. With few exceptions, the true coronal lines are below 300 A, and the general necessity for and complexity of grazing incidence optics has made it difficult to obtain high resolution spectroheliograms.

The coronal X-spectrum: Problems and prospects

Solar X-rays from 8–12 A have been observed with an ion chamber photometer and fluxes derived from the observations after an assumption concerning the spectral distribution. The time variation of the X-ray flux correlates well with the radio flux, plage index, and sunspot number. Comparisons of X-ray and optical events are given; flares seem to produce soft X-rays, but some soft X-ray bursts are apparently not associated with flares. The total energy involved in the soft X-ray bursts may be a significant amount of the total flare radiation.

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Observation of the solar soft X-ray component; study of its relation to transient and slowly-varying phenomena observed at other wavelengths

X-ray imaging with multiple-pinhole cameras using a posteriori holographic image synthesis.

Solar X-ray data from rocket and satellite-borne equipment, discussing spectrum of quiet corona and active region

J. H. Underwood

Papers

Solar X-rays.