Auroral X-ray Research Articles

Auroral X-ray pulsations in the 1.2- to 4-second period range

Journal of Geophysical Research (1896-1977)Volume 76, Issue 16 p. 3811-3815 Letters Auroral X-ray pulsations in the 1.2- to 4-second period range J. R. Barcus, J. R. BarcusSearch for more papers by this authorR. R. Brown, R. R. BrownSearch for more papers by this authorR. H. Karas, R. H. KarasSearch for more papers by this authorT. J. Rosenberg, T. J. RosenbergSearch for more papers by this authorH. Trefall, H. TrefallSearch for more papers by this authorK. Bronstad, K. BronstadSearch for more papers by this author J. R. Barcus, J. R. BarcusSearch for more papers by this authorR. R. Brown, R. R. BrownSearch for more papers by this authorR. H. Karas, R. H. KarasSearch for more papers by this authorT. J. Rosenberg, T. J. RosenbergSearch for more papers by this authorH. Trefall, H. TrefallSearch for more papers by this authorK. Bronstad, K. BronstadSearch for more papers by this author First published: 1 June 1971 https://doi.org/10.1029/JA076i016p03811Citations: 4AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume76, Issue16Space Physics1 June 1971Pages 3811-3815 RelatedInformation

Auroral pulsations—Television image and X-ray correlations

The association between auroral X-rays and luminosity has been studied for pulsating auroras by coordinated observations with a balloon borne X-ray detector and a ground based image intensifier-television system viewing the N 2 + ING emissions. The degree of correlation between X-ray and luminosity variations was found to depend upon the number of pulsating forms common to both detector fields of view. Correlation was good in those cases when one form occupied the optical field of view but poor when several, asynchronously pulsating, forms were present.

A Preliminary Report on Balloon Observation of Auroral X-Rays at Syowa Station, Antarctica

A Preliminary Report on Balloon Observation of Auroral X-Rays at Syowa Station, Antarctica

Auroral X-rays and their association with rapidly changing auroral forms

Auroral X-rays and their association with rapidly changing auroral forms

Microburst phenomena: 1. Auroral-zone X rays

Abstract : High-time resolution x-ray equipment flown from Ft. Churchill, Manitoba, Canada on August 11, 1965 provides evidence for species of auroral zone x-ray microbursts with an asymmetric time profile. These asymmetric microbursts are characterized by a rise of the form 1 - e to the power (-t/tau sub R) where tau sub R is about 30 milliseconds, and a decay of the form of e to the power (-t/tau sub D) where tau sub D is about 200 milliseconds, and a typical peak flux for the largest events of Jo (Ex-ray > 60 keV) of about 100 photons/cm squared sec at 10 g/sq. cm. An episode of these asymmetric bursts was observed in the early morning hours (after 4:30 local time) and an episode of the more common symmetric microbursts began after 9:30 local time. The fast rise times, and the lack of dispersion approximately = or > 10 milliseconds in the x-ray bursts observed at different energies implies restrictions on the nature, and propagation of the parent electron microbursts. (Author)

Simultaneous balloon measurements of auroral X-rays during slowly varying ionospheric absorption events

In the present paper we report the results of simultaneous balloon measurements of auroral X-rays in northern Scandinavia during slowly varying ionospheric absorption events. It is found that during typical events the electron precipitation starts north of L = 6·5 and spreads southwards to at least L ≈ 4·5 with speeds of about 500 m/s. The events apparently have a large longitudinal extension with the southern border aligned almost geomagnetically east—west. After the expansion the electron precipitation seems to decay uniformly over the area which was covered during the expanding phase. Faster pulsations are often observed superimposed on the general trend of the events and microbursts are probably always present.

A persisting 24-sec periodicity in auroral X-rays interrupted by sudden geomagnetic impulses

Observations are presented of an auroral X-ray event, which showed very persistent regular intensity variations. The sequence of regular variations was interrupted by two sudden geomagnetic impulses, hut probably reappeared later on. This result puts some restraints on the nature of possible modulation mechanisms.

Energy-dependent modulation in auroral X-ray pulsations

Energy dependent modulation in auroral X ray pulsations from balloon flight observations, discussing electron precipitation and visual aurora associations

Observations on the association of auroral luminosity with auroral X-rays and cosmic noise absorption

Simultaneous observations of auroral luminosity and bremsstrahlung X-rays from the same balloon payload are reported here. Comparison of the balloon measurements with riometer records has shown the same variety of associations that appear in other studies of auroral phenomena. Because the photometer and scintillation counter geometries are fixed relative to each other and view equivalent regions of the sky at the production layer, it has been possible to investigate behavioral differences in the low and high energy portions of the precipitated electron spectrum with more certainty than when comparing balloon and ground-based observations. Certain aspects of the present observations suggest that temporal variations in these two energy ranges are rather independent, on occasion. These observations support the suggestion that two mechanisms having characteristically different energy spectra control the acceleration and/or precipitation of energetic electrons. Correlations of auroral luminosity with X-rays then depend upon the degree of coupling between the mechanisms.

Discussion of paper by A. G. Petschek, ‘Interpretation of satellite detector counter rates’

Petschek [1963] has computed a value of 2·10−4 for the fission β counting efficiency of the lead-shielded Anton Geiger counter in the Injun satellite. Since the efficiency of heavily shielded counters to nonpenetrating electrons is of importance in the interpretation of satellite radiation measurements [Van Allen et al., 1963; Hess, 1963], I wish to draw attention to several errors in Petschek's paper. I wish also to comment briefly on the thick target electron bremsstrahlung process, as it is relevant to the problem of space radiation hazards and of the interpretation of auroral X-ray measurements as well as to the efficiency of shielded Geiger counters.

Auroral zone x-ray pulsations in the 1- to 15-second period range

Auroral zone X-ray pulsations in the 1- to 15-second period range, observed at Macquarie Island, Australia, on March 5, 1962, and College, Alaska, on June 29, 1962, are described. Both observations indicate that the time intervals between the X-ray bursts are not unique; the average intervals over the pulsation events were 7.8 and 8.8 seconds, respectively. These observations indicate that the pulsation periods in this range are determined by acceleration or pitch-angle redistribution processes in the equatorial plane rather than any fundamental, periodic motion of the electrons along lines of force in the geomagnetic field.

Auroral X-rays, electron bombardment and trapped radiation

Recent measurements of the characteristics of energetic particles incident on the top of the atmosphere, presumably precipitated from the earth's trapped radiation, are discussed. The incident flux varies widely, from 10 8 to 10 10 particles/cm 2 sec for electrons. Other characteristics of the flux also vary from event to event, independently of the flux and of each other. During the most intense events, which are the ones which correspond to aurorae, the lifetime of an electron in the trapping region is only a few seconds. Clearly, violent processes go on during such events, so violent as to destroy the effectiveness of the trap. Several mechanisms, including one presented in an appendix to the paper, are examined and it is concluded that no one process accounts for all observations.

Scintillation-counter observations of auroral X rays during the geomagnetic storm of May 12, 1959

Auroral X rays were observed at 10 g/cm2 atmospheric depth over Minneapolis on May 12, 1959, with a balloon-borne NaI scintillation spectrometer in the energy range 22 to 263 kev. This event accompanied the low-energy solar cosmic rays that also produced some γ rays in the atmosphere. Energy spectra of the X rays were obtained after correcting for the presence of these γ rays. The peak in the auroral X-ray intensity was found to be associated with the passage of the aurora at the zenith. The electron spectrum responsible for the X rays has been determined and found to be in agreement with the observations of electron spectrum of the outer radiation belt.

Auroral x-rays, cosmic rays, and related phenomena during the storm of February 10-11, 1958

Balloon observations were made during the auroral storm of February 10- 11, 1958, at Minneapolis. Strong x-ray bursts in two groups were detected. The groups appeared coincident with two large magnetic bays, with strong radio noise absorption, and with the passage across the zenith of a very large amount of auroral luminosity. From the x-ray intensity and measured energies, an electron current of 0.6 x 10/sup 6/ electrons /cm/sup 2// scc was present. These electrons ionizing the upper D layer accounted for the increased cosmic noise absorption. The x-rays themselves carried 1000 times less energy than the electrons and could not provide sufficient ionization for the observed radio absorption. Visual auroral fornis during this storm are reported to have lower borders at thc 200 to 300 km level. There is thus a difficulty in bringing the electrons to the D layer without ani accompanying visible aurora. A cosmic-ray decrease accompanied the storm and was observed to be from 4 to 6% at sea level, 21% in the balloon altitude ionization, and 15% in total energy influx at 55 deg geomagnetic latitude. Compared with the great intensity of the magnetic and auroral phenomena in this storm, the cosmic-ray modulation was notmore » exceptionally large. (auth)« less