Engineering topics
Publications and source records attributed to Strong, K. T..
Observations of an X4 flare of May 19, 1984 using the VLA and the SMM X-ray Polychromator are discussed. The 6 cm radio source remained stationary throughout the decay phase. Combined with other evidence, this indicates that the flare was magnetically confined and did not disrupt the complex structure of its region. The observed structures may be associated with a neutral sheet connecting the two bipoles.
The Solar-A satellite being prepared by the Institute for Sapce and Astronautical Sciences (ISAS) in Japan is dedicated to high energy observations of solar flares. The Soft X Ray Telescope (SXT) is being prepared to provide filtered images in the 2 to 60 A interval. The flight model is now undergoing tests in the 1000 foot tunnel at MSFC. Launch will be in September 1991. Earlier resolution and efficiency tests on the grazing incidence mirror have established its performance in soft x rays. The one-piece, two mirror grazing incidence telescope is supported in a strain free mount separated from the focal plane assembly by a carbon-epoxy metering tube whose windings and filler are chosen to minimize thermal and hygroscopic effects. The CCD detector images both the x ray and the concentric visible light aspect telescope. Optical filters provide images at 4308 and 4700 A. The SXT will be capable of producing over 8000 of the smallest partial frame images per day, or fewer but larger images, up to 1024 x 1024 pixel images. Image sequence with two or more of the five x ray analysis filters, with automatic exposure compensation to optimize the charge collection by the CCD detector, will be used to provide plasma diagnostics. Calculations using a differential emission measure code were used to optimize filter selection over the range of emission measure variations and to avoid redundancy, but the filters were chosen primarily to give ratios that are monotonic in plasma temperature.
The problem of deriving the temperature of the coronal plasma from soft X-ray spectra is discussed. Spectral atlas scans of the soft X-ray spectrum from the Flat Crystal Spectrometer on the Solar Maximum Mission are compared with theoretical predictions of the relative intensities of some of the brighter lines to determine which line intensity ratios give the most reliable temperature diagnostics. The techniques considered include line widths, He-like G ratios, intensity ratios, and ratios of lines formed by different elements. It is found that the best temperature diagnostics come from the ratios of lines formed by successive ionization stages of the same element.
Since the repair of the Solar Maximum Mission (SMM) spacecraft, the Flat Crystal Spectrometer (FCS) has recorded many high temperature spectra of helium-like ions under a wide variety of coronal conditions including active regions, long duration events, compact events, and double flares. The plasma density and temperature are derived from the ratios R and G, where R = f/i, G = (f + i)/r, and r, f, and i denote the resonance, forbidden, and intercombination line fluxes. A new method for obtaining the density and temperature for events observed with the FCS aboard SMM is presented. The results for these events are presented and compared to earlier results, and the method is evaluated based on these comparisons.
Coordinated multiwaveband observations of five new cycle active regions were obtained during the Coronal Magnetic Structures Observing Campaign in 1987. SMM X-ray polychromater maps provided accurate temperature and emission measure diagnostics, and VLA maps provided information on microwave structure, spectrum, and polarization. The results were used to separate contributions from the two dominant microwave emission mechanisms, thermal bremsstrahlung and gyroresonance.
A study of type III activity at meter-decameter wavelengths in the preflare phase of the February 3, 1986 flare is presented, using data obtained with the Clark Lake Multifrequency Radioheliograph. This activity is compared with similar type III burst activity during the impulsive phase, and it is found that there is a displacement of burst sources between the onset and end times of the activity. A comparison of this displacement at three frequencies suggests that the type III emitting electrons gain access progressively to diverging and different field lines relative to the initial field lines. The energetics of the type III emitting electrons are inferred from observations and compared with those of the associated hard X-ray emitting electrons. The soft X-ray data from SMM-XRP show enhanced emission measure, density, and temperature in the region associated with the preflare type III activity.
In this investigation of flare energetics, researchers sought to establish a comprehensive and self-consistent picture of the sources and transport of energy within a flare. To achieve this goal, they chose five flares in 1980 that were well observed with instruments on the Solar Maximum Mission, and with other space-borne and ground-based instruments. The events were chosen to represent various types of flares. Details of the observations available for them and the corresponding physical parameters derived from these data are presented. The flares were studied from two perspectives, the impulsive and gradual phases, and then the results were compared to obtain the overall picture of the energics of these flares. The role that modeling can play in estimating the total energy of a flare when the observationally determined parameters are used as the input to a numerical model is discussed. Finally, a critique of the current understanding of flare energetics and the methods used to determine various energetics terms is outlined, and possible future directions of research in this area are suggested.
Reseachers compare results with those in the chapter by Moore et al. (1980), who reached five main conclusions about the gradual phase: (1) the typical density of the soft X-ray emitting plasma is between 10 to the 11th power and 10 to the 12th power cm-3 for compact flares and between 10 to the 10th power and 10 to the 11th power cm-3 for a large-area flare; (2) cooling is by conduction and radiation in roughly equal proportions; (3) continual heating is needed in the decay phase of two-ribbon flares; (4) continual heating is probably not needed in compact events; (5) most of the soft-X-ray-emitting plasma results from chromospheric evaporation. The goal was to reexamine these problems with the data from the Solar Maximum Mission (SMM) and other supporting instruments as well as to take advantage of recent theoretical advances. SMM is capable of measuring coronal temperatures more accurately and with a better cadence than has been possible before. The SMM data set is also unique in that the complete transit of an active region was observed, with soft X-ray and UV images being taken every few minutes. Researcher's were therefore able to establish the pre-flare conditions of the region and see whether anything has changed as a result of the flare. The assumptions made in attempting to determine the required plasma parameters are described. The derived parameters for the five prime flares are presented, and the role of numerical simulations is discussed.
Three flares observed by the Soft X-Ray Polychromator on the Solar Maximum Mission were studied. Flare light curves from the Flat Crystal Spectrometer and Bent Crystal Spectrometer were examined for rapid signal variations. Each flare was characterized by an initial fast (less than 1 min) burst, observed by the Hard X-Ray Burst Spectrometer (HXRBS), followed by softer gradual X-ray emission lasting several minutes. From an autocorrelation function analysis, evidence was found for quasi-periodic fluctuations with rise and decay times of 10 s in the Ca XIX and Fe XXV light curves. These variations were of small amplitude (less than 20%), often coincided with hard X-ray emissions, and were prominent during the onset of the gradual phase after the initial hard X-ray burst. It is speculated that these fluctuations were caused by repeated energy injections in a coronal loop that had already been heated and filled with dense plasma associated with the initial hard X-ray burst.
SMM soft X-ray data and Sacramento Peak Observatory H-alpha observations are combined in a study of the impulsive phase of a solar flare. A blue asymmetry, indicative of upflow motions, was observed in the coronal Ca XIX line during the soft X-ray rise phase. H-alpha redshifts, indicative of downward motions, were observed simultaneously in bright flare kernels during the period of hard X-ray emission. It is shown that, to within observational errors, the impulsive phase momentum transported by the upflowing soft X-ray plasma is equivalent to that of the downward moving chromospheric material.
The XRP was designed to measure the following temporal and spatial properties of the active and flaring Sun: electron temperature, departures from steady state, ion kinetic temperatures, and electron density. The Bent Crystal Spectrometer (BCS) is capable of measuring the broadening and blue shifts often observed in the impulsive phase of flares. The six simultaneous line fluxes indicative of six different temperatures of formation observable by the Flat Crystal Spectrometer (FCS) allows the derivation of the differential emission measure of the plasma at each raster point. During the operational periods of the XRP hundreds of flares of C-level (GOES classification) were observed and brighter in both the FCS and BCS, including 5 X-flares. Associated theoretical work in atomic physics, stimulated in part by the promise of XRP measurements, has benefitted from the experimental data on solar plasmas which the XRP has provided in abundance.
Observations of a flare that began in soft X-rays at 20:37 UT on April 12, 1980 at the west limb of the sun are discussed. The observations of the flare and postflare loops are first described, and the Solar Maximum Mission data are interpreted in terms of the temperature, density, and geometry of the emitting regions. The observed postflare cooling time is compared with that expected from radiation, conduction, and enthalpy flux. The loop model is discussed, and the observed events are compared with other proposed models.
The limb flare of 1980 November 18 at 14:51 UT is studied with the X-ray instruments on board the Solar Maximum Mission (SMM). Evidence is found for release of a significant fraction, 10 percent or more, of the flare energy before the impulsive hard X-ray burst. In the impulsive phase the hard X-rays emitted during the rapidly varying part of the burst are observed on the limb, at a level consistent with the chromosphere. During the final stages of the hard X-ray burst, when the fast time structure has disappeared, the hard X-rays clearly come from the corona, at which time the spectrum is softer. Throughout the decay phase of the flare the X-rays also originate in the corona. It is concluded that initially the flare energy is deposited below the transition zone, from which point the chromospheric plasma is ablated. When this plasma has expanded into the corona to the energy release site, particle acceleration associated with such energy release is quenched. The altitude of this site is estimated at 6000 + or - 1500 km above the photosphere. The sequence of observations is consistent with the bulk of the energy being contained in suprathermal protons, in the energy region 100-1000 keV, during the impulsive phase.
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.
A new kind of sunspot-associated microwave source was detected by Alissandrakis and Kundu (1982). The observed emission came predominantly from a ring structure with a size between that of the umbra and the penumbra. It was thought that the newly discovered structure could be the product of the low gyroresonance opacity when the angle between the magnetic field and the line of sight is close to zero. The present investigation has the objective to study the roles played by the geometrical effect of gyroresonance absorption and by the low-temperature flux tubes above the relevant sunspot, taking into account 6 cm observations made with the aid of a radio telescope and X-ray observations conducted with the X-ray Polychromator (XRPO on the Solar Maximum Mission) (SMM) satellite.
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.
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.
Results from the analysis of flares observed by the Solar Maximum Mission (SMM) and a recent rocket experiment are discussed. Evidence for primary energy release in the corona through the interaction of magnetic structures, particle and plasma transport into more than a single magnetic structure at the time of a flare and a complex and changing magnetic topology during the course of a flare is found. The rocket data are examined for constraints on flare cooling, within the context of simple loop models. These results form a basis for comments on the limitations of simple loop models for flares.