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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Solar activity observed in X-rays and the EUV from OSO 7

Spectroheliograms obtained with the EUV spectroheliograph aboard OSO 7 between 1.7 and 400 A with a spatial resolution of at least 20 x 20 arc seconds are described, and results of an initial analysis of the Goddard X-ray polarimeter measurements are given and discussed in the light of current flare theories. The EUV observations are consistent with a picture in which coronal enhancement overlying an active region is made up of a nested set of arches or loops, with foot-points in regions of opposite magnetic polarity. The outermost arches are coolest, while those nearer the center are hotter. Along a given field line there is a temperature gradient such that the highest temperature occurs at the highest point of the magnetic arch. Polarimeter data provide evidence for polarization of about 20% in a number of X-ray bursts.

Thomas, R. J.↗
NASA NTRS1976

Thermodynamic history of a solar active region observed in X-rays

The structure and energy content of an active coronal volume during its early history are investigated using soft X-ray images secured with the glancing-incidence telescope on Skylab. During the late stages of emerging-flux-region activity, the maximum temperatures exceeded 6.5 million K. At that time, the temporal rate of change in thermal energy content was about 10 to the 25th power ergs/s and was comparable to the rate of energy loss by radiation. Fluctuations in the energy content of the X-ray source region imply that this coronal active region was probably not in energy equilibrium during the five days of observation.

Teske, R. G.↗
NASA NTRS1979

Lyman-alpha rocket spectra and models of the quiet and active solar chromosphere based on partial redistribution diagnostics

Absolute intensity Lyman-alpha profiles with a spatial resolution of 0.8 min and a spectral resolution of 50 mA were obtained for network and cell regions in the quiet sun, umbral and penumbral areas of a sunspot, two plages, and a quiescent prominence of the limb. Weak limb brightening shown by the Lyman-alpha cores and wings are consistent with predictions derived from partial redistribution line transfer calculations. Through use of a comoving two-level partial redistribution code which conserves mass flux, unequal red and blue Lyman-alpha peak intensities may be interpreted as flow velocities near 20,000 K. Outflows in the plages and downflows in the network are also noted. A model of a mean quiet sun chromosphere consistent with the Lyman-alpha integrated intensity, the Lyman continuum slope, and the millimeter continuum is presented.

Basri, G. S.↗
NASA NTRS1979

Analysis of X-ray and EUV spectra of solar active regions

Data acquired by two flights of an array of six Bragg crystal spectrometers on an Aerobee rocket to obtain high spatial and spectral resolution observations of various coronal features at soft X-ray wavelengths (9-23A) were analyzed. The various aspects of the analysis of the X-ray data are described. These observations were coordinated with observations from the experiments on the Apollo Telescope Mount and the various data sets were related to one another. The Appendices contain the published results, abstracts of papers, computer code descriptions and preprints of papers, all produced as a result of this research project.

Strong, K. T.↗
NASA NTRS1980

The coronal and transition region temperature structure of a solar active region

Using measurements of EUV and X-ray spectral lines, the differential emission measure vs electron temperature from the transition region to the corona of an active region (electron temperature between 100,000 and 5,000,000 K) is derived. The total emission measure and radiative losses are of the order 3 x 10 to the 48th/cu cm and 4 x 10 to the 26th ergs/sec, respectively. The emission measure at electron temperatures greater than approximately 1,000,000 K (i.e. that mainly responsible for the X-ray emission) is about 75% of the total. The use of the Mg x line at 625 A as an indicator of coronal electron density is also examined. A set of theoretical energy balance models of coronal loops in which the loop divergence is a variable parameter is presented and compared with the observations.

Levine, R. H.↗
NASA NTRS1982

Energy-Storage Modules for Active Solar Heating and Cooling

34 page report describes a melting salt hydrate that stores 12 times as much heat as rocks and other heavy materials. Energy is stored mostly as latent heat; that is, heat that can be stored and recovered without any significant change in temperature. Report also describes development, evaluation and testing of permanently sealed modules containing salt hydrate mixture.

Parker, J. C.↗
NASA NTRS1981

Surface magnetic fields during the solar activity cycle

The behavior of the magnetic field of the sun as measured in the Fe I 5250 A line is summarized. A latitudinal distribution of the fields observed over 13.5 yr is presented, and episodic formation of the polar fields (about 6 gauss) from a poleward drift originating at the sunspots is noted. Weak magnetic fields (-2 to +2) reach a maximum two years before the maximum in the average field. The total flux remains constant from minimum to maximum, with strong magnetic flux exhibiting an equatorward drift; both strong and new flux appear mostly around sunspots. The appearance of new flux implies the decay of flux elsewhere on the sun, because of the measured constancy of total flux; total replacement of the surface flux can occur within ten days. Field annihilation is concentrated in the active latitudes, where strong opposite polarity fields occur close together.

Howard, R.↗
NASA NTRS1984

Depth of origin of solar active regions

Observations show that the individual bipolar magnetic regions on the sun remain confined during their decay phase, with much of the magnetic field pulling back under the surface, in reverse of the earlier emergence. This suggests that the magnetic field is held on a short rein by subsurface forces, for otherwise the region would decay entirely by dispersing across the face of the sun. With the simple assumption that the fields at the surface are controlled from well-defined anchor points at a depth h, it is possible to relate the length l of the bipolar region at the surface to the depth h, with h about equal to l. The observed dimensions l about equal to 100,000 km for normal active regions, and l about equal to 10,000 km for the ephemeral active regions, indicate comparable depths of origin. More detailed observational studies of the active regions may be expected to shed further light on the problem.

Parker, E. N.↗
NASA NTRS1984

Three-dimensional structures of two solar active regions from VLA observations at 2, 6, and 20 centimeter wavelengths

Three-dimensional structures of two active region groups are determined from observations with the Very Large Array (VLA) at 2, 6, and 20 cm. One of the groups exhibits a single magnetic loop of length approximately 10 to the 10th cm. The 2 cm radiation is mostly thermal bremsstrahlung and originates from the footprints of the loop. The 6 and 20 cm radiation is dominated by low-harmonic gyroresonance radiation and originates from the upper portion of the legs or the top of the loop. The loop broadens toward the apex. The top of the loop is not found to be the hottest point, but two temperature maxima on either side of the loop apex are observed, which is consistent with the model proposed for long loops. From 2 and 6 cm observations it can be concluded that the electron density and temperature cannot be uniform in a plane perpendicular to the axis of the loop; the density should decrease away from the axis of the loop.

Shevgaonkar, R. K.↗
NASA NTRS1985

Diurnal anisotropy during solar activity cycle twenty and diffusion-convection model

Underground muon telescope data obtained at Embudo and Neutron monitor data obtained at Deep River are divided into two sets; one covers the ascending phase of the cycle (1965-70) and the other covers the descending phase (1971-76). The amplitude of diurnal anisotropy calculated from the data does not agree with the value predicted by the simplified version of the Diffusion-Convection Model (DCM); the discrepancy is worse for neutron data.

Ahluwalia, H. S.↗
NASA NTRS1985

Change of cosmic ray anisotropy with solar activity

Muon telescope data at various depths underground in Yakutsk within energy range 10 to 300 GeV for 1957 to 1984 are analyzed. The 22-year variation of the interplanetary magnetic field aligned component is found. The variation is caused by interaction of heliomagnetosphere with the local galactic field and interstellar wind.

Kravtsov, N. G.↗
NASA NTRS1984

EUV airglow during active solar conditions. II - Emission between 530 and 930 A

Instrumentation on the Astrobee F sounding rocket on June 27, 1980 gathered EUV airglow data in the 530-930 A range. The 2-4 A resolution data were examined specifically for O II emission lines below 800 A, which were centered at 537-539 A. The emision was attributed to doublet and quartet components and exhibited a branching ratio of 3. A separate identification was made of O II emissions at 581 A. Inclusion of the 2s2p(4)2P state is therefore recommended in photoinization models of cometry and planetary atmospheres.

Gentieu, E. P.↗
NASA NTRS1984

A case for submergence of magnetic flux in a solar active region

In NOAA Active Region 2372 (April 1980), 4 x 10 to the 20th maxwells of magnetic flux concentrated in an area 30 arcsec across disappeared overnight. Vector magnetograms show that all components of the magnetic field weakened together. If the field had weakened through diffusion or fluid flow, 90 percent of the original flux would still have been detected by the magnetograph within a suitably enlarged area. In fact there was a threefold decrease in detected flux. Evidently, magnetic field was removed from the photosphere. Since the disappearing flux was located in a region of low magnetic shear and low activity in H-alpha and Ly-alpha, it is unlikely that the field dissipated through reconnection. It is argued that the most likely possibility is that flux submerged. The observations suggest that even during the growth phase of active regions, submergence is a strong process comparable in magnitude to emergence.

Rabin, D.↗
NASA NTRS1985

Multiwavelength observations of a preflare solar active region using the VLA

A preflare active region was studied using the Very Large Array at 2, 6, and 20 cm. At 2 cm the region is composed of two components located in regions of opposite polarity. Both components are preheated prior to the impulsive onset of a flare. However, one component develops new structures during preburst phase, and the burst occurs in this location. It is believed that the new structures represent emerging flux regions which interact with an overlying loop to produce a neutral sheet, which ultimately is responsible for triggering the flare.

Kundu, M. R.↗