Direct measurements of density in the thermosphere.
Falling sphere, solar XUV radiation absorption and pressure gauge mass spectrometry for density measurements of thermosphere, comparing results and noting discrepancies
MASS SPECTROMETRY↗
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Observation of absorption edges in the extreme ultraviolet by transmittance measurements through thin unbacked metal films.
X-ray absorption edge observation by transmittance measurements through thin unbacked metal films in XUV as function of wavelength
METAL FILM↗
A three dimensional model of thermospheric - 1 - Heat input and eigenfunctions
Three dimensional thermospheric model developed from solar XUV radiation and corpuscular heating during geomagnetic storms of atmospheric system
Mayr, H. G.↗
A three dimensional model of thermospheric dynamics. I - Heat input and eigenfunctions
Thermospheric dynamics three dimensional model in terms of atmospheric system eigenfunctions, deriving formulas for solar XUV and corpuscular heating during geomagnetic storms
Mayr, H. G.↗
X-ray spectroscopy of solar active regions and flares.
Review of some recent contributions of X-ray spectroscopy to knowledge about solar active regions and flares. As an example of the importance of X-ray spectroscopy, it is pointed out that, while there are no emission lines from highly ionized silicon in the visible spectrum, the XUV spectrum has emission lines from SiIX through SiXIV. Jordan's (1969) calculations of ionization equilibria for silicon and iron are illustrated by diagrams and discussed. The observation of SiXIV gives evidence for regions having electron temperatures from 5 to 20 million deg. The ability to record the corona against the disk of the sun has enabled Van Speybroeck et al. (1970) to identify many bright diffuse X-ray emitting regions with remnants of old active regions of the type giving rise to unipolar magnetic regions. The physical characteristics of the hot coronal plasma associated with chromospheric flares are outlined on the basis of current observations.
Neupert, W. M.↗
Structure of the chromosphere-corona transition region.
The structure and energy balance of the chromosphere-corona transition region is investigated by means of a static, planar model which is compared with the results of XUV-resonance-line observations. In this model, the transition region is heated by thermal conduction from the corona and cooled by radiative losses. Comparison of the model with observational results implies that this is the dominant process in the energy balance of the transition region, and that the base of the transition region is inherently nonstatic and/or nonplanar. The model explains the observational finding of Noyes et al. (1970) that the number density and the downward heat flux both increase by the same factor from quiet regions to active regions.
Moore, R. L.↗
Skylab and its solar astronomy experiments.
The functional characteristics of the Skylab are considered together with general information concerning the spacecraft and its equipment. The Skylab solar instruments are examined, giving attention to two H-alpha telescopes, a white light coronograph, X-ray spectrographic telescopes, a UV scanning polychromator/spectroheliometer, a dual X-ray telescope, an XUV spectrograph/spectroheliograph, and instruments of X-ray/UV solar photography. The Skylab solar observing programs are discussed along with aspects of astronaut training and details regarding the control and display devices of the spacecraft.
Schneider, W. C.↗
The quiet sun
An up-to-date textbook of solar physics is presented. The solar structure and processes, and the interior are described along with the photosphere, the chromosphere, and the corona. The strongest Fraunhofer lines, visible coronal lines, and coronal UV, XUV, and X-ray lines are listed.
Gibson, E. G.↗
On the Fe XXIV emission in the solar flare of 1973 June 15
The double ribbon flare of 1973 June 15 was observed in the XUV wavelength region with the NRL objective grating spectroheliograph during the Skylab missions. The Fe XXIV emissions at 192.1 and 255.2 A are prominent in the early phase of the flare. The Fe XXIV emission is centered over the neutral line, forming a bridgelike structure between magnetic regions of opposite polarity. This is unlike the emission pattern of He II, the transition zone ions, and Fe IX-XVI, which are relatively brighter in the adjacent flare ribbons overlying strong vertical magnetic field. An electron density of 5 times 10 to the 10th per cu cm for the Fe XXIV emission region is deduced from the observational data, and the cooling rate is briefly discussed.
Widing, K. G.↗
Solar flares
A review of the knowledge about solar flares which has been obtained through observations from the earth and from space by various methods. High-resolution cinematography is best carried out at H-alpha wavelengths to reveal the structure, time history, and location of flares. The classification flares in H alpha according to either physical or morphological criteria is discussed. The study of flare morphology, which shows where, when, and how flares occur, is important for evaluating theories of flares. Consideration is given to studies of flares by optical spectroscopy, radio emissions, and at X-ray and XUV wavelengths. Research has shown where and possibly why flares occur, but the physics of the instability involved, of the particle acceleration, and of the heating are still not understood.
Zirin, H.↗
The reconnection of magnetic field lines in the solar corona
Skylab XUV coronal spectroheliograms and photospheric magnetograms are compared. This comparison shows that, as new bipolar magnetic fields emerge through the solar surface into the corona, the new coronal fields interact with the old ones in a manner that suggests the reconnection of the field lines.
Sheeley, N. R., Jr.↗
Unfolding first and second order diffracted radiation when using synchrotron radiation sources - A technique
A technique is presented of using a single calibrated XUV detector for radiometric measurements of synchrotron radiation after the radiation passes through a monochromator that produces a mixture of first- and second-order diffracted radiation. Irradiance measurements are made with the synchrotron source operating at two different energies for the orbiting electrons. The known change in the spectral distribution produced by the electron energy change is used to calculate the flux in both first and second order. The dependence of the precision of these determinations on the two detected currents and on the detector calibration at both first- and second-order wavelengths is calculated. Experimental results using the National Bureau of Standards synchrotron (SURF-I) are presented, and anticipated results for the new NBS electron storage ring (SURF-II) are calculated.
Saloman, E. B.↗
Synoptic maps of solar coronal hole boundaries derived from He 2 304 A spectroheliograms from the manned skylab missions
The disk boundaries of coronal holes have been determined from He II 304 A spectroheliograms which were taken with the Naval Research Laboratory slitless XUV spectrograph during the manned Skylab missions. These boundaries are plotted by Carrington rotation as synoptic charts in both the standard rectangular as well as polar-view projections. The periods of time for which boundaries were determined are 24 May through 28 June 1973 (first manned Skylab mission), 2 August through 24 September 1973 (second manned mission), and 21 November 1973 through 2 February 1974 (third manned mission); the Carrington rotations covered (in part or totally) are 1601 and 02; 160r, 1604, 05 and 06; and 1608, 09 and 10, respectively.
Bohlin, J. D.↗
Coronal changes associated with a disappearing filament
Skylab/ATM observations of a disappearing filament near the center of the solar disk are described using XUV and H-alpha spectroheliograms, X-ray filterheliograms, and photospheric magnetograms. The temperature of the coronal plasma as the filament disappeared is estimated to have been in excess of 6 million K, and it is noted that the time history of the soft X-ray and microwave fluxes displayed the gradual-rise-and-fall (GRF) signature, suggesting that the present event may have properties that are characteristic of a wide class of long-duration X-ray and radio events. A comparison with other spatially resolved long-duration X-ray events indicates that all such long-lived bursts involve transients in the outer corona and that some two-thirds of them involve either the eruption or the major activation of a prominence. It is also found that long-lived events are characterized by the appearance of new emission loops in the lower corona during the declining phase of the X-ray emission and that these loops sometimes disappear after the X-ray events and sometimes remain indefinitely.
Sheeley, N. R., Jr.↗
The quiet sun in the extreme ultraviolet
Observations of the quiet sun with an XUV spectrometer during the Skylab mission are reported for the chromosphere, transition region, and corona. The changing structure of the network is examined over the temperature range from 10,000 to 1.5 million K, and the distribution of intensities in the cell interiors and the network are examined from the standpoint of creating characteristic models. Observations of traces of periodic oscillations at 300 s in the cells for temperatures not exceeding 20,000 K are reported together with the absence of any periodic contributions at higher temperatures or periodic effects at any height in the network elements. Frequent nonperiodic brightenings are observed, and their characteristics discussed. Observations of the increased thickness of the transition region in coronal holes, as well as other properties, are discussed in limited detail. Observations of the center-to-limb behavior of transition-region and coronal lines are used to construct coronal models, and the assumptions of spherical symmetry evaluated from the intensity data. The effects of spicules on the limb and disk data are discussed in relation to the observations.
Reeves, E. M.↗
Doppler wavelength shifts of transition zone lines measured in Skylab solar spectra
Wavelengths of lines of the transition-zone ions Si IV, C IV, O IV, N V, and O V are observed to be redshifted relative to the wavelengths of chromospheric lines in XUV spectra obtained from the normal-incidence spectrograph on Skylab. The spectra cover the wavelength range from 1200 to 1565 A and were obtained with the slit positioned over chromospheric network and cell regions, on coronal holes, and above the limb. The network-area and coronal-hole spectra were obtained near the disk center. Only some of the spectra show redshifted transition-zone lines. The observed shifts are between 0.03 and 0.08 A, implying velocities of 15 km/s or less. The amount of wavelength shift does not always appear to be the same for lines of different ions. The shifts imply that descending plasma in the solar atmosphere produces more emission than ascending plasma at temperatures between approximately 70,000 and 200,000 K.
Doschek, G. A.↗
On the white dwarf HZ 43 as an extreme-ultraviolet source
It is confirmed by atmospheric modeling that both the visual continuum and the XUV spectrum (60 to 600 A) of HZ 43 can be fitted self-consistently with the emergent flux from a stellar atmosphere having an effective temperature of about 125,000 K and log g of at least 7. An examination of theoretical white-dwarf cooling sequences and estimates of the stellar luminosity indicate that the parameters of HZ 43 are consistent with a hot white dwarf of 0.6 to 1.2 solar masses. The age is estimated to be as short as 100,000 years, raising the possibility that the star may have ejected a planetary nebula or may be surrounded by an expanding H II region. It is concluded that the detection of a planetary nebula shell or an H II region around HZ 43 may provide an astrophysical test of the direct neutrino-electron interaction.
Durisen, R. H.↗
High-latitude observations of solar wind streams and coronal holes
Interplanetary scintillation observations of the solar wind velocity during 1973 and the first part of 1974 reveal several corotating high-speed streams. These streams, of heliographic latitudes from +40 deg to -60 deg, have been mapped back to the vicinity of the sun and have been compared with coronal holes identified in wide band XUV solar images taken during the manned portions of the Skylab mission. There is some evidence that the high-speed streams are preferentially associated with coronal holes and that they can spread out from the hole boundaries up to about 20 deg in latitude. However, this association is not one to one; streams are observed which do not map back to coronal holes, and holes are observed which do not lie at the base of streams. To the extent that a statistical interpretation is possible the association is not highly significant, but individual consideration of streams and holes suggests that the statistical result is biased somewhat against a strong correlation.
Ricket, B. J.↗