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At least 739 records · Page 41
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NASA NTRS1977

Time delay occultation data of the Helios spacecrafts and preliminary analysis for probing the solar corona

S-band time delay measurements were collected from the spacecrafts Helios A and B during three solar occultations in 1975/76 within heliocentric distances of about 3 and 215 solar radii in terms of range, Doppler frequency shift, and electron content. A description is given concerning some characteristic features of the methods of measurement and data processing. Typical data sets are discussed to probe the electron density distribution near the sun (west and east limb as well) including the outer and extended corona. Steady-state and dynamical aspects of the solar corona are presented and compared with earth-bound K-coronagraph measurements. Using a weighted least squares estimation 3 parameters of an average coronal electron density profile are derived in a preliminary analysis to yield electron densities of about 130 billion; 100 million; 7 million/cu m at r?3; 65; 215 solar radii. Transient phenomena are discussed and a velocity of propagation v approximately 900 km/s for plasma ejecta from a solar flare is determined from an extraordinary set of Helios B electron content measurements on April 30/May 1, 1976.

Edenhofer, P.↗
NASA NTRS1978

Magnetohydrodynamics of atmospheric transients. I - Basic results of two-dimensional plane analyses

The dynamic behavior of transients in a stratified atmosphere in the presence of a magnetic field is investigated with the two-dimensional plane formulation, i.e., the formulation in which variations of the flow and magnetic field are confined within a plane. It is pointed out that, in the plane formulation, the noncompressible transverse waves (often called the Alfven waves) are excluded. The compressible responses of the atmosphere are then examined with a temperature perturbation (simulating a sudden local release of energy by a flare) as functions of the configuration of magnetic field and field strength. It is shown that (1) in the open (mostly radial) magnetic field, the propagation of 'bubble-like' density enhancements, the coronal transients, result; while (2) in the closed (mostly azimuthal) field, the density enhancement forms a pair of 'horns' near the foot points of field lines similar to that often observed by coronagraphs after flares. Discussions in interpreting the results in terms of the anisotropic propagation of the fast and slow waves (or shocks) are presented together with consideration of possible consequences with the inclusion of the transverse waves.

Nakagawa, Y.↗
NASA NTRS1977

A study of the background corona near solar minimum

Equatorial and polar K and F coronal components during the declining phase of the solar cycle are studied through use of the white light coronagraph data obtained by Skylab. At this phase of the solar cycle, streams and holes dominate the equatorial corona (approximately 50 and 30% of the time, respectively) between 2.5 and 5.5 solar radii; however, two episodes are noted when equatorial background density of the corona could be distinguished. The derived background density is less than 15% below values predicted by the models of Newkirk (1967) and Saito (1970). The brightness of the F-corona is also discussed.

Saito, K.↗
NASA NTRS1977

Coronal mass-ejections-kinematics of the 19 December 1973 event

A detailed description of the observed kinematics of the coronal disturbance of December 19, 1973, is presented along with inferences about the temperatures, densities, magnetic fields, and electric currents within the event. This disturbance consisted of the eruption of a previously quiescent prominence, an associated ejection of coronal material, and the destruction of a large coronal streamer. Observations of the prominence and the corona with a scanning spectroheliometer and a white-light coronagraph aboard Skylab before, during, and after the prominence eruption are discussed, and the temperature and density in the eruptive prominence are traced as the prominence rose to a height of 3 solar radii over 7 hr. The results obtained are shown to reinforce previous arguments that the material comprising the bulk of the mass ejected from the corona in transient events arises from the low corona rather than from the eruptive prominence, which may accompany the coronal mass ejection.

Schmahl, E.↗
NASA NTRS1978

Motions and mass changes of a persistent coronal streamer

The Skylab white light coronagraph observed a coronal streamer during five successive limb passages between June 1 and August 6, 1973. Measurements of the streamer's latitude, brightness and polarization during three east-limb passages show that: (1) the streamer's axis migrated southward from 25 deg N at first east-limb passage to 11 deg N at second east-limb passage to 8 deg N at third east-limb passage, (2) the streamer's mass and mass gradient with height varied by 20-50% from one east-limb passage to the next, (3) the streamer's longitudinal extent was observed to be less on successive east-limb passages, and (4) mass changes (distinct from coronal transients) occurring over hours were detected during at least two limb passages. The streamer was found to be associated with a complex of solar activity consisting of active regions and filaments.

Poland, A. I.↗
NASA NTRS1979

Magnetohydrodynamic models of coronal transients in the meridional plane. II - Simulation of the coronal transient of 1973 August 21

A two-dimensional planar MHD model of solar atmospheric transient events is used to simulate the flare-associated events of August 21, 1973. This event, observed in H-alpha, He II 304 A, soft X-ray, and coronal white light, provided sufficient information (especially in the latter diagnostic) for an assessment to be made of the model's ability to simulate major features of an actual solar event. It was found that a thermodynamic input pulse based on data provided by the NASA Marshall Space Flight Center-Aerospace Corporation X-ray telescope (S-056) on Skylab was sufficient to produce the global geometry, shock and contact-surface velocities, excess mass contours, and energy budget which were, for the most part, observed by the High Altitude Observatory white-light coronagraph (S-052) on Skylab in the form of a forerunner and coronal transient.

Dryer, M.↗
NASA NTRS1979

The association of coronal mass ejection transients with other forms of solar activity

Coronal mass-ejection transients observed with the white-light coronagraph on Skylab are found to be associated with several other forms of solar activity. There is a strong correlation between such mass-ejection transients and chromospheric H-alpha activity, with three-quarters of the transients apparently originating in or near active regions. It is inferred that 40% of transients are associated with flares, 50% are associated with eruptive prominences solely (without flares), and more than 70% are associated with eruptive prominences or filament disappearances (with or without flares). Nine of ten flares that displayed apparent mass ejections of H-alpha-emitting material from the flare site could be associated with coronal transients. Within each class of activity, the more energetic events are more likely to be associated with an observable mass ejection.

Munro, R. H.↗
NASA NTRS1979

Radio and white-light observations of the 1973 August 21 coronal transient

A coronal transient, which occurred on August 21, 1973, has been observed simultaneously in white light and at decameter radio wavelengths. The radio observations were obtained with a two-dimensional swept-frequency array (called the Teepee Tee). The white-light observations consist of a series of photographs taken by the High Altitude Observatory's coronagraph aboard Skylab. The radio emission associated with the transient was continuum in nature and lasted for almost 5 hours. The source of emission was observed to be cospatial with the lower part of one of the secondary white-light loops. A lower limit of 0.6 solar radius for the depth (extension along the line of sight) of this part of the transient was derived from considerations of radio-wave propagation in the corona. The radio source showed no dispersion of height with frequency, and, therefore, the emission is attributed to gyrosynchrotron radiation. Based on this assumption, the magnetic-field strength in the lower part of the loop is estimated to be in the 2.0-4.5-gauss range at a height of 2.1 solar radii from the center of the sun.

Gergely, T. E.↗
NASA NTRS1980

Dynamics of flare sprays

During solar cycle No. 20 new insight into the flare-spray phenomenon has been attained due to several innovations in solar optical-observing techniques (higher spatial resolution cinema-photography, tunable passband filters, multislit spectroscopy and extended angular field coronagraphs). From combined analysis of 13 well-observed sprays which occurred between 1969-1974 it is concluded that (1) the spray material originates from a preexisting active region filament which undergoes increased absorption some tens of minutes prior to the abrupt chromospheric brightening at the 'flare-start', and (2) the spray material is confined within a steadily expanding, loop-shaped (presumable magnetically controlled) envelope with part of the materials draining back down along one or both legs of the loop.

Tandberg-Hanssen, E.↗
NASA NTRS1980

Measurements of coronal kinetic temperatures from 1.5 to 3 solar radii

A rocket-borne Lyman-alpha coronagraph has been used to make the first measurements of the spectral line profile of resonantly scattered hydrogen Lyman-alpha coronal radiation between 1.5 and 3 solar radii. These data provide, for the first time, direct measurements of coronal temperatures above 1.5 solar radii. Data were obtained in a coronal hole, quiet region, and streamer. The widths of the profiles from the quiet region decrease with height and correspond to a steady decrease in hydrogen kinetic temperature, with increasing radius, from about 2.5 million K at r = 2 solar radii to about 1 million K at r = 9 solar radii. In the coronal hole the measured line widths indicate a kinetic temperature of 1.8 million K at r = 2.5 solar radii.

Kohl, J. L.↗
NASA NTRS1981

Solar radio bursts of spectral type II, coronal shocks, and optical coronal transients

An examination is presented of the association of solar radio bursts of spectral type II and coronal shocks with solar flare ejecta observed in H-alpha, the green coronal line, and white-light coronagraphs. It is suggested that fast-moving optical coronal transients should for the most part be identified with piston-type phenomena well behind the outward-traveling shock waves that generate type II radio bursts. A general model is presented which relates type II radio bursts and coronal shocks to optically observed ejecta and consists of three main velocity regimes: (1) a quasi-hemispherical shock wave moving outward from the flare at speeds of 1000-2000 km/sec and Alfven Mach number of about 1.5; (2) the velocity of the piston driving the shock, on the order of 0.8 that of the shock; and (3) the regime of the slower-moving H-alpha ejecta, with velocities of 300-500 km/sec.

Maxwell, A.↗
NASA NTRS1982

EUV spectroscopic plasma diagnostics for the solar wind acceleration region

Possibilities are considered for probing physical conditions in the solar corona with strong EUV resonance lines from ions such as N V, O VI, Ne VIII, Mg X, and Si XII. Through measurements of the intensities and profiles of EUV spectral lines with coronagraphic instrumentation employing normal incidence reflecting optics, it is possible to acquire information on electron, proton, and ion temperatures and velocity distributions; electron, H I, and ion densities; mass flow and nonthermal velocities; and chemical abundances. This information will provide critical empirical constraints on physical processes responsible for plasma heating, solar wind acceleration, and transport of mass, momentum, and energy in the solar corona, as well as providing constraints on theoretical models for solar and stellar coronae and mass loss.

Kohl, J. L.↗
NASA NTRS1982

A magnetohydrodynamic theory of coronal loop transients

The physical and geometrical characteristics of solar coronal loop transients are described in an MHD model based on Archimedes' MHD buoyancy force. The theory was developed from interpretation of coronagraphic data, particularly from Skylab. The brightness of a loop is taken to indicate the electron density, and successive pictures reveal the electron enhancement in different columns. The forces which lift the loop off the sun surface are analyzed as an MHD buoyancy force affecting every mass element by imparting an inertial force necessary for heliocentrifugal motion. Thermal forces are responsible for transferring the ambient stress to the interior of the loop to begin the process. The kinematic and hydrostatic buoyancy overcome the gravitational force, and a flux rope can then curve upward, spiralling like a corkscrew with varying cross section around the unwinding solar magnetic field lines.

Yeh, T.↗
NASA NTRS1981

Feasibility study of the solar scientific instruments for Spacelab/Orbiter

The feasibility and economics of mounting and operating a set of solar scientific instruments in the backup Skylab Apollo Telescope Mount (ATM) hardware was evaluated. The instruments used as the study test payload and integrated into the ATM were: the Solar EUV Telescope/Spectrometer; the Solar Active Region Observing Telescope; and the Lyman Alpha White Light Coronagraph. The backup ATM hardware consists of a central cruciform structure, called the "SPAR', a "Sun End Canister' and a "Multiple Docking Adapter End Canister'. Basically, the ATM hardware and software provides a structural interface for the instruments; a closely controlled thermal environment; and a very accurate attitude and pointing control capability. The hardware is an identical set to the hardware that flow on Skylab.

Leritz, J.↗
NASA NTRS1982

Dynamics of the eruptive prominence of 6 May 1980 and its relationship to the coronal transient

The active prominence of the 6 May 1980 has been observed between 5.23 and 10.22 UT with the Ultraviolet Spectrometer and Polarimeter (UVSP) on board the Solar Maximum Mission (SMM) satellite. Intensities of 1548 A line of CIV and dopplershifts have been derived. A motion of the magnetic tube maintaining the prominence material is noted. This motion is followed by a coronal transient observed with the Coronagraph and Polarimeter (C/P) between 11 and 13 UT. It is suggested that the event is related to a MHD wave induced by a flare occurring behind the solar disk, and a MHD modeling of the perturbation is proposed.

Mein, N.↗
NASA NTRS1982

Simultaneous radio scattering and white light observations of a coronal transient

Reports that a coronal transient observed by the Solwind coronagraph off the west limb of the sun was also seen in the spectral broadening observations of the Helois-2 2.3 GHz radio signal. These simultaneous data are compared and applied to studies of the shock front. UT difference images show a time difference of up to 2 h between shock and white light occurrences. Helios and Voyager shock speed measurements are consistent, implying that the event observed by Helios is a shock. These coronal transient data show that the shock front is ahead of the white light front, but additional observations of larger events will contribute information to the understanding of coronal transient evolution as they propagate away from the sun.

Woo, R.↗
NASA NTRS1982

NASA-ESA Spacelab systems and programs; Proceedings of the Seminar, Washington, DC, April 23, 24, 1981

Topics discussed include the development status of the Space Shuttle and Spacelab, with attention to Spacelab subsystem performance capabilities and Shuttle-Spacelab flight operations; Spacelab data management and software for science applications, ESA and Space Shuttle pointing systems, and the Space Shuttle's Office of Space and Terrestrial Applications (OSTA)-1 payload. Also covered are the lessons learned from the first Spacelab mission, the pallet-only mode verification flight of the second Spacelab mission, the objectives of the Spacelab mission D1, its role in the German space program, and its implementation, the impact of Spacelab on space-based life sciences research, the high resolution, large area modular reflector array X-ray telescope to be used by Spacelab, and Space Shuttle contamination effects on UV coronagraphic observations.

Moore, J. W.↗
NASA NTRS1982

General contamination criteria for optical surfaces

Physical models are developed for establishing criteria to decide on the acceptable contamination level of optical devices in space-borne conditions. Optical systems can be degraded in terms of decreased throughput, i.e., transmissivity or reflectivity, or increases in the total integrated scatter (TIS). Performance losses can be caused by particulate accretion, molecular film accretion, and impact cratering. A quantitative relationship is defined for film thickness and loss of throughput. Formulas are also developed for cases where induced surface defects are larger than the desired viewing wavelengths, or smaller or of the same order of the observed wavelengths. The techniques are used to quantify the degradation of a VUV solar coronagraph, a VUV stellar telescope, and a solar cell due to TIS. Applications are projected for estimating the contamination sensitivity of specific instruments, assessing the contamination hazard from known particulates, or to define clean room standards.

Bremer, J. C.↗