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Smith, J. B., Jr.

Publications and source records attributed to Smith, J. B., Jr..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Nonpotential magnetic fields at sites of gamma-ray flares

The relation between the degree of nonpotentiality of photospheric magnetic fields and the occurrence of gama-ray flares is examined to determine whether there are special signatures of the stressed fields for this type of flare. Observations of the flares in the active region of April 1984 (AR 4474) are analyzed, showing that the big flare initiated at the location on the magnetic neutral line where the field deviated the most from a potential field. The nonpotential signatures of AR 4474 are compared with those of four other regions. The results suggest that gamma-ray flares are associated with strongly nonpotential fields that extend over relatively larger lengths of the magnetic neutral line that the fields associated with flares that do not produce gamma-ray events.

Hagyard, M. J.↗
NASA NTRS1988

Flare onset at sites of maximum magnetic shear

Observations of the transverse component of the Sun's photospheric magnetic field obtained with the MSFC vector magnetograph show where the fields are nonpotential. The correlation was studied between locations of nonpotential fields and sites of flare onset for four different active regions. The details of the active region AR 4711 are outlined. Similar results are presented for three other regions: AR 2372 (April 1980), AR 2776 (November 1980), and AR 4474 (April 1984). For all four regions it is shown that flares initiate at sites on the magnetic neutral line where the local field deviates the most from the potential field. The results of this study suggest that flares are likely to erupt where the shear is equal to or greater than 85 degrees, the field is equal to or greater than 10000 G, and there is strong shear (equal to or greater then 80 degress) extending over a length equal to or greater than 8000 km.

Hagyard, M. J.↗
NASA NTRS1988

Nonpotential magnetic fields at sites of gamma ray flares

The relation between the degree of nonpotentiality of photospheric magnetic fields and the occurrence of gamma ray flares is examined. The parameter delta phi (magnetic shear) and the strength of the magnetic field intensity are used as measures of the degree of nonpotentiality, where delta phi is defined as the angular difference between the observed direction of the transverse component of the photospheric field and the direction of the potential field prescribed by the distribution of measured photospheric flux. An analysis of the great flare of April 24 to 25, 1984 is presented as an example of this technique to quantify the nonpotential characteristics of the pre-flare magnetic field. For this flare, which produced a large gamma ray event, strong shear and high field strengths prevailed over an extended length of the magnetic neutral line where the flare occurred. Moreover, the flare began near the area of strongest measured shear (89 to 90 deg). Four other flaring regions were analyzed; one of these produced a moderate gamma ray event while the other three did not produce detectable gamma rays. For all four regions the flares were located in the area where the field was not nonpotential, regardless of the class of flare. The fields of the gamma ray flares were compared with those associated with the flares without gamma rays, and little distinction was found in the degree of magnetic shear. The major difference is seen in the extent of the sheared field: for gamma ray events, the field is sheared over a longer length of the neutral line.

Hagyard, M. J.↗
NASA NTRS1984

A multiwavelength study of a double impulsive flare

Solar Maximum Mission (SMM) and ground-based observations are given for two flares which occurred 3 min apart in the same section of the active region. The physical characteristics of the two flares are derived and compared, and the main difference between them is noted to be in the preflare state of the coronal plasma at the flare site. These data suggest that the plasma filling the flaring loops absorbed most of the energy released during the impulsive phase of the second flare, so that only a fraction of the energy could reach the chromosphere to produce mass motions and turbulence. Since a study of the brightest flares observed by SMM shows that at least 43 percent of them are multiple, the situation presently studied may be quite common, and the difference in initial plasma conditions could explain at least some of the large variations in observed flare parameters.

Strong, K. T.↗
NASA NTRS1984

Modeling of energy buildup for a flare-productive region

A self-consistent MHD model of shearing magnetic loops is used to investigate magnetic energy buildup in active region AR 2372 (Boulder number), in the period of April 5-7, 1980. The magnetic field and sunspot motions in this region, derived using observational data obtained by the Marshall Space Flight Center Solar Observatory, suggest the initial boundary conditions for the model. It is found that the plasma parameters (i.e., density, temperature, and plasma flow velocity) do not change appreciably during the process of energy buildup as the magnetic loops are sheared. Thus, almost all of the added energy is stored in the magnetic field. Furthermore, it is shown that dynamical processes are not important during a slow buildup (i.e., for a shearing velocity less than 1 km/s). Finally, it is concluded that the amount of magnetic energy stored and the location of this stored magnetic energy depend on the initial magnetic field (whether potential or sheared) and the magnitude of the shearing motion.

Wu, S. T.↗
NASA NTRS1984

Progress in the study of homologous flares on the sun. II

Studies of groups of homologous flares in active regions in 1980 were performed using a variety of space and ground-based instruments. The properties of three of the groups are described and combined to form a possible sequence of events.

Woodgate, B. E.↗
NASA NTRS1984

Homologous flares and the evolution of NOAA Active Region 2372

A detailed record of the evolution of NOAA Active Region 2372 has been compiled by the FBS Homology Study Group. It was one of the most prolific flare-producing regions observed by SMM. The flares occurred in distinct stages which corresponded to particular evolutionary phases in the development of the active region magnetic field. By comparison with a similar but less productive active region, it is found that the activity seems to be related to the magnetic complexity of the region and the amount of shear in the field. Further, the soft X-ray emission in the quiescent active region is related to its flare rate. Within the broader definition of homology adopted, there was a degree of homology between the events within each stage of evolution of AR2372.

Strong, K. T.↗
NASA NTRS1982

Active region magnetic fields inferred from simultaneous VLA microwave maps, X-ray spectroheliograms, and magnetograms

The VLA maps at 6-cm wavelength discussed here are generated from observations of a solar active region (NOAA 2363) on March 29 and 30, 1980. The X-ray spectroheliograms were acquired for this region in the lines of O VIII, Ne IX, Mg XI, Si XIII, S XV, and Fe XXV. It is found that the peaks of X-ray and 6-cm emission do not coincide but that the sources in the two wavelength domains tend to overlap. These facts are seen as evidence for the existence of opacity mechanisms other than thermal bremsstrahlung. To quantify this assertion, differential emission measures are computed to derive densities and temperatures. Using these and calculated force-free magnetic fields from Kitt Peak magnetograms, an assessment is made of the mechanism of gyroresonance absorption at low harmonics of the electron gyrofrequency as the source of opacity responsible for the microwave features. It is concluded that large-scale currents must be present in the active region loops to account for the bright 6-cm sources far from sunspots.

Schmahl, E. J.↗
NASA NTRS1982

Vector magnetic field evolution, energy storage, and associated photospheric velocity shear within a flare-productive active region

Sheared photospheric velocity fields inferred from spot motions for April 5-7, 1980, are compared with both transverse magnetic field orientation changes and with the region's flare history. Rapid spot motions and high inferred velocity shear coincide with increased field alignment along the longitudinal neutral line and with increased flare activity, while a later decrease in velocity shear precedes a more relaxed magnetic configuration and decrease in flare activity. It is estimated that magnetic reconfiguration produced by the relative velocities of the spots could cause storage of about 10 to the 32nd erg/day, while flares occurring during this time expended no more than about 10 to the 31st erg/day.

Krall, K. R.↗
NASA NTRS1980

Morphology and spatial distribution of XUV and X-ray emissions in an active region observed from Skylab

The morphology and spatial distribution of loops in an active region observed from Skylab are described. The active region loops were classified into hot loops with temperatures of 2 to 3 million K observed in coronal lines and X-rays, and cool loops with temperatures of 500,000 to one million K observed in transition zone lines. The brightest hot coronal loops in the active region are predominantly low-lying, compact, closely-packed, showing greater stability than the transition-zone loops, which are fewer in number, are large, and slender. The observed aspect ratio of the hot coronal loops in the range of 0.1 and 0.2 are almost two orders of magnitude larger than those of the Ne VII loops.

Cheng, C.-C.↗
NASA NTRS1980

On the physics of a long decay X-ray event

The paper discusses the long decay X-ray event which appeared as an expanding loop system on the solar limb on 13-14 Aug. 1973 which was also observed temporally and spectrally. A one-dimensional hydrodynamic study was undertaken to investigate increasing and decreasing phases of the event; it was shown that the inferred temperature gradients along the loops during the heating phase are consistent with unrestricted dynamic and conductive flows along the magnetic field lines. It was concluded that it cannot be definitely stated that enhanced emission at the tops of the loops is due to pressure gradients along the field lines; also, the large emission measure variations in the 10 to the 5th to 10 to the 6th K plasma during the event's decline may be due to the temperature dependence of radiative decay within a multiloop configuration.

Krall, K. R.↗
NASA NTRS1979

Physical parameter analysis of an intense, compact subflare

Results of analysis of Skylab X-ray proportional counter data (10-s averages) and X-ray telescope filtergrams for the August 9, 1973 (SN/M2) subflare from McMath 12474 (NOAA AR 185) are presented. The event flux profiles and profiles of temperature, volume emission-measure, and a quantity equivalent to thermal energy content are shown. Using the proportional counter data, a peak temperature in excess of 20,000,000 K at 1552:05 UT, a peak volume emission measure of 7 x 10 to the 48th per cu cm at 1553:25 UT, and a peak value of thermal energy content of 2 x 10 to the 16th evgs/cm to the 3/2 power at 1552:45 UT were derived. Based on the analysis of spatially-resolved X-ray images during the period near flare-peak through flare-decay, the flare is observed to be both intense and compact and to consist of at least two identifiable loops whose volumes remained essentially unchanged throughout the event.

Wilson, R. M.↗
NASA NTRS1978

Solar activity during Skylab: Its distribution and relation to coronal holes

Solar active regions observed during the period of Skylab observations (May 1973-February 1974) were examined for properties that varied systematically with location on the sun, particularly with respect to the location of coronal holes. Approximately 90 percent of the optical and X-ray flare activity occurred in one solar hemisphere (136-315 heliographic degrees longitude). Active regions within 20 heliographic degrees of coronal holes were below average in lifetimes, flare production, and magnetic complexity. Histograms of solar flares as a function of solar longitude were aligned with H alpha synoptic charts on which active region serial numbers and coronal hole boundaries were added.

Speich, D. M.↗
NASA NTRS1978

Analysis of X-ray observations of the 15 June 1973 flare in active region NOAA 131

Observations and analyses of the 1B/M3 flare of 15 June, 1973 in active region NOAA 131 (McMath 12379) are presented. The X-ray observations, consisting of broadband photographs and proportional counter data from the Skylab/ATM NASA-MSFC/Aerospace S-056 experiment, are used to infer temperatures, emission measures, and densities for the flaring plasma. The peak temperature from the spatially resolved photographs is 25,000,000 K, while the temperature from the full-disk proportional counter data is approximately 15,000,000 K. The density is 3 times 10 to the 10th/cu cm. The X-ray flare emission appears to come primarily from two low-lying curvilinear features lying perpendicular to and centered on the line where the photospheric longitudinal magnetic field is zero. Similarities in the preflare and postflare X-ray emission patterns indicate that no large-scale relaxation of the coronal magnetic configuration was observed. Also discussed are H-alpha and magnetic field observations of the flare and the active region. Finally, results of numerical calculations, including thermal conduction, radiative loss, and chromospheric evaporation, are in qualitative agreement with the decay phase observations.

Krall, K. R.↗
NASA NTRS1977

Morphology and physical parameters of a solar flare

The chromospheric and coronal morphology of the flare of June 15, 1973, (1B/M3) in NOAA active region 131 (McMath 12379) is discussed, and results of quantitative analysis of Skylab soft X-ray observations of the event are presented. H-alpha and white-light observations reveal evidence of emerging flux near the site of the H-alpha flare onset. Preflare and early flare filament activity and its spatial and temporal correlation with the flare are discussed. Spatially resolved soft X-rays are compared with H-alpha and magnetic-field measurements. Full-disk high-temporal-resolution soft X-ray flux measurements and time profiles of the resultant temperature and density calculations are also presented which yield a peak temperature of about 14.2 million K and a peak electron density of approximately 3.5 deg 10 to the -10th power per cu cm and show a preflash-phase temperature rise to about 9 million K. The peak values should be compared with the respective values of approximately 25 million K and 4.5 by 10 to the -10th power per cu cm deduced from the spatially resolved data.

Smith, J. B., Jr.↗
NASA NTRS1977

Film calibration for the Skylab/ATM S-056 X-ray telescope

The sensitometry and film calibration effort for the Skylab/ATM S-056 X-ray telescope is summarized. The apparatus and procedures used are described together with the two types of flight film used, Kodak SO-212 and SO-242. The sensitometry and processing of the flight film are discussed, and the results are presented in the form of the characteristic curves and related data. The use of copy films is also discussed.

Henze, W., Jr.↗
NASA NTRS1977

Prominence mass ejections and their effects on the corona. I - The eruptive prominence of 21 August 1973 and the surge of 4 December 1973

A previous treatment of prominence-induced coronal responses is extended to X-ray and H-alpha observations of an eruptive prominence and a surge by using a time-dependent two-dimensional single-fluid MHD computer code that neglects dissipation and radiation. The two events and their observation are described, and some physical parameters of the coronal plasma are derived. The observed coronal responses to ascending prominences are analyzed with the aid of the cited computer code. The results obtained indicate that: (1) the coronal response to an eruptive prominence may be simulated with a density-dominated pressure pulse of long duration; (2) the response to a surge may be simulated with a temperature pulse of short duration; and (3) the investigated eruptive-prominence disturbance injected a mass of approximately 10 to the 16th power g into the corona and was associated with a coronal transient having a calculated velocity of 275 km/s at a distance of 1.5 solar radii.

Smith, J. B., Jr.↗