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Brueckner, G. E.

Publications and source records attributed to Brueckner, G. E..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Measurements of spectrally integrated atmospheric transmittance in the O2 Schumann-Runge bands and derived oxygen column densities - 76-102 km

Atmospheric transmittances integrated over wavelength intervals corresponding approximately to the (15-0) through (4-0) Schumann-Runge bands of O2 have been determined from EUV solar spectra (wavelengths between 1768 and 1948 A) photographed at seven altitudes between 102 and 76 km with a rocket-borne spectrograph having a resolution of 0.07 A. The observed transmittances are compared with atmospheric transmittances predicted from three models of the O2 absorption cross section. The predicted transmittances have also been used to derive column densities of atmospheric O2 from the observations. The results are compared with values calculated from the U.S. Standard Atmosphere (1976) and with oxygen column densities determined by Prinz and Brueckner (1977) from EUV solar spectra of the Schumann-Runge continuum (wavelength below 1750 A) and of the H-Lyman alpha line (1216 A) recorded on the same films used in the present research. The comparisons test the utility of the models for studies of atmospheric photochemistry, suggest which models may be best for this purpose, and indicate how the models can be improved.

Longmire, M. S.↗
NASA NTRS1979

EUV continua of solar flares 1420-1960 A

Measurements of absolute continuum intensities in the wavelength range 1420-1960 A are presented for the SN subflare of 1973 August 9 and the 2B flare of 1973 September 7, observed from the NRL spectrograph aboard Skylab. Continuum measurements are also given for two active-region plages, which are used for background nonflaring levels. Major enhancement of the flare continuum intensity above the plage backgrounds occurs in the Si I 3P and 1D continua. The observed brightness-temperature minimum of the plages is approximately 310 K above the quiet-sun minimum, and occurs at longer wavelength. The earliest flare brightness-temperature minima are approximately 200 K above the plage minimum, and also at longer wavelength. The observed decay time of the flare brightness temperature, which is comparable to the Solrad 9 X-ray decay time, is much longer than the Ulmschneider radiative relaxation time for the 1973 September 7 flare and marginally longer for the 1973 August 9 flare, suggesting continuous excess heating of the plage temperature minimum region throughout the period of our flare observations.

Cook, J. W.↗
NASA NTRS1978

Emission lines of H2 in the extreme-ultraviolet solar spectrum

A sunspot EUV spectrum covering the wavelength range from 1175 to 1714 A with high spatial and spectral resolution is examined which contains about 200 lines not previously reported in solar spectra. Many of the lines are identified as transitions in the Lyman bands of H2. It is shown that the H2 lines are photoexcited not only by H L-alpha, as reported previously, but also by the strong transition-region lines of C II, Si IV, and O IV. The line intensities are analyzed as far as is possible at present, and differences between the quiet chromosphere and the sunspot chromosphere are deduced. The polarization of the observed lines is briefly discussed, the importance of the H L-alpha fluorescence mechanism for the excitation of the H2 Lyman bands is demonstrated, and it is concluded that the H2 lines could also be observable in stars of spectral type later than the sun.

Jordan, C.↗
NASA NTRS1978

CO fluorescence in the extreme-ultraviolet solar spectrum

Emission lines in the fourth positive system of CO have been identified in the extreme-ultraviolet solar spectrum 1540-1660 A. These lines are excited by the C IV transition-zone lines at 1548 and 1551 A. They are strong in the spectrum of a sunspot and in parts of the adjacent active region. Some of them appear as weak, broad emission features in the quiet sun.

Bartoe, J.-D. F.↗
NASA NTRS1977

Forbidden lines of the solar corona and transition zone - 975-3000 A

Forbidden lines characteristic of plasmas at temperatures of 50,000 to 3 million K are observed in ATM UV spectra. Identifications, accurate wavelengths, ionization classes, intensities, and half-widths are presented. Coronal blends with He II at 1640 A are noted. Variations in nonthermal velocities with limb distance are observed. Doppler shifts in the coronal lines observed on the disk may be related to the solar wind. The coincidence of two lines with F IV(3P-5S) is evidence for atomic fluorine in the sun.

Sandlin, G. D.↗
NASA NTRS1977

Extreme ultraviolet spectroheliograph ATM experiment S082A

The XUV spectroheliograph, Apollo Telescope Mount experiment S082A, is described. The instrument was a slitless Wadsworth grating spectrograph that employed photographic recording. The grating was of 4-m radius, ruled with 3600 grooves/mm. By rotating the grating to positions where the normal was at 255 A or 400 A, the spectral ranges 175-335 A and 320-480 A, respectively, were covered with 2-sec of arc spatial resolution. Close to the normal the resolution reached 2 sec of arc, but at the extreme limit, 630 A, it was 10 sec of arc or worse. The aberrations of the instrument are discussed in detail as are the provisions necessary to maintain optimum imagery and reliability in a space environment. During the mission about 1020 exposures were made covering 171-335 A or 320-630 A.

Tousey, R.↗
NASA NTRS1977

Extreme ultraviolet spectrograph ATM experiment S082B

The extreme-ultraviolet double-dispersion photographic spectrograph for the Apollo Telescope Mount (ATM) experiment S082B on Skylab is described. Novel features were the use of a predisperser grating with a ruling whose spacing varied approximately linearly with distance for the purpose of increasing the instrument speed by reducing the astigmatism and a photoelectric servosystem to stabilize to 1 sec of arc the solar image at various near-limb positions. The 970-3940-A range was covered in two sections with effective resolving power of approximately 30,000 from 1100 A to 1970 A. The spatial resolution was 2 x 60 solar sec of arc. During the Skylab mission 6400 exposures were made with the instrument pointed by an astronaut at selected and recorded solar positions.

Bartoe, J.-D. F.↗
NASA NTRS1977

Observations of the O2 column density between 120 and 70 km and absorption cross section in the vicinity of H Lyman alpha

From solar spectra obtained during the re-entry of Calroc 4 the optical depth of the atmosphere in the wavelength interval 1213-1219 A has been obtained for altitudes between about 120 and 70 km. The data are consistent with the interpretation that molecular oxygen is the primary absorbing species under these conditions if the values of the O2 cross section in the 1216.2- to 1217.2-A region are approximately those of Ogawa (1968) and the O2 column densities in the 80-km region are approximately those derived from the 8-0 and 11-0 Schumann-Runge bands observed during the same flight.

Prinz, D. K.↗
NASA NTRS1976

Study of the relationship between solar activity and terrestrial weather

Evidence for some connection between weather and solar related phenomena is presented. Historical data of world wide temperature variations with relationship to change in solar luminosity are examined. Several test methods for estimating the statistical significance of such phenomena are discussed in detail.

Sturrock, P. A.↗
NASA NTRS1976

A.t.m. observations on the X u.v. emission from solar flares

The paper summarizes observations of selected solar flares made with a far-UV spectroheliograph (190-465 A) and a UV spectrograph (900-1900 A) aboard Skylab. The emission lines used in the present analysis are identified, and three events are described in detail: the flare of June 15, 1973, a small subflare observed on August 9, 1973, and the flare of January 21, 1974. Ultraviolet images of two other events are also presented in an attempt to sketch a general picture of a flare as seen in this spectral region. It is found that a small kernel seems to be the source of the primary energy release of a flare. The size, electron density, and ion temperature of a typical kernel are estimated, and it is noted that hot clouds of coronal gas at 20 million K surrounded the observed kernels. It is speculated that flare kernels might be very thin channels through which high-energy particles, originating in deep layers, are ejected into the corona.

Brueckner, G. E.↗
NASA NTRS1976

Spectroscopic far ultraviolet observations of transition zone instabilities and their possible role in a pre-flare energy build-up

Highly flare-productive newly emerging active regions are characterized by numerous small low-lying loops which frequently show a chaotic pattern. Flare activity in such a region subsides as the chaotic loop structures relax and expand into a bipolar configuration. The transition zone in such an active region is highly unstable, as shown by broadened and shifted nonthermal line profiles of medium-ionized elements like Si III, Si IV, and C IV. These transition-zone instabilities, which occur as isolated events in active regions of low flare productivity, are often observed prior to flares. Transition-zone instabilities can be traced to the footpoints of active loops and seem to be accompanied by heating of the loop. The loops vary in size and show differing degrees of activity, with the brightest and most compact ones seemingly being in a pre-flare state which results in the catastrophic energy release along the loop during a flare.

Brueckner, G. E.↗
NASA NTRS1975

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.↗
NASA NTRS1975

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.↗
NASA NTRS1975

XUV observations of coronal magnetic fields

Spectroheliograms obtained with the Naval Research Laboratory's Extreme Ultraviolet Spectrograph (S082A) on Skylab are compared with Kitt Peak National Observatory magnetograms. A principal result is the characteristic reconnection of flux from an emerging bipolar magnetic region to previously existing flux in its vicinity. Examples of the disappearance of magnetic flux from the solar atmosphere are also shown. The results of a particularly simple, potential field calculation are shown for comparison with the Skylab observations.

Sheeley, N. R., Jr.↗
NASA NTRS1975

Ultraviolet emission line profiles of flares and active regions

A preliminary description of ultraviolet spectra of active regions and flares, photographed from Skylab by the Naval Research Laboratory's UV spectrograph, is given. The findings can be summarized as follows: (1) Line profiles of medium-ionized lines (transition-zone lines) show the most pronounced broadenings and shifts in flares and flare-like events; (2) typical full widths at half maximum of these lines correspond to Doppler velocities of 70 km/s; (3) shifts of the same magnitude can be observed; (4) intersystem lines are not broadened or shifted; (5) forbidden coronal lines and intersystem lines become enhanced in the flare spectrum at the moment when the turbulence seen in the allowed transitions disappears; and (6) a very broad line at 1354.2 A, which appears only in flare spectra, seems to be the forbidden transition 3P(1)-3P(0) of Fe XXI.

Brueckner, G. E.↗