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Bornmann, P. L.

Publications and source records attributed to Bornmann, P. L..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Flare rates and the McIntosh active-region classifications

Multiple linear regression analysis was used to derive the effective solar flare contributions of each of the McIntosh classification parameters. The best fits to the combined average number of M- and X-class X-ray flares per day were found when the flare contributions were assumed to be multiplicative rather than additive. This suggests that nonlinear processes may amplify the effects of the following different active-region properties encoded in the McIntosh classifications: the length of the sunspot group, the size and shape of the largest spot, and the distribution of spots within the group. Since many of these active-region properties are correlated with magnetic field strengths and fluxes, we suggest that the derived correlations reflect a more fundamental relationship between flare production and the magnetic properties of the region. The derived flare contributions for the individual McIntosh parameters can be used to derive a flare rate for each of the three-parameter McIntosh classes. These derived flare rates can be interpreted as smoothed values that may provide better estimates of an active region's expected flare rate when rare classes are reported or when the multiple observing sites report slightly different classifications.

Bornmann, P. L.↗
NASA NTRS1994

McIntosh active-region class similarities and suggestions for mergers

McIntosh active-region classifications reported during a five-year period were examined to determine similarities among the classes. Two methods were used extensively to determine these similarities. The number of transitions among classes were used to determine the most frequent transitions out of each class, and the alternative classes reported for the same region by different sites were used to establish which classes were neighboring classes. These transition frequencies and neighboring classes were used to identify classes that could be eliminated or merged with other classes. Class similarities were used to investigate the relative importance of several pairs of decisions that occur within a single McIntosh parameter. In particular, the redundancy of parameters in some classes was examined, and the class similarities were used to identify which of these parameters could be eliminated. Infrequently reported classes were also considered, and suggestions for mergers were made when similarities between classes could be identified.

Bornmann, P. L.↗
NASA NTRS1992

Fluid flow in a jet and the Ca XIX line profiles observed during solar flares

The present study considers two types of fluid models as methods for reproducing the blueshifts and line broadening observed in soft X-ray lines during the rise of solar flares. The fluid models representing the laminar flow of material in a jet and through a pipe were used to derive the velocity at each location in the flow. The optimal values for the free parameters in the jet model were within the ranges expected for solar flare conditions. The jet was much smaller than typical flare volumes estimated from spatial images, but the resulting densities were consistent with the upper limit of densities derived using density-sensitive line ratios. This supports previous reports of small filling factors and is interpreted as evidence for a chromospheric origin for the flow. Stability analysis indicates that, although the laminar jet can reproduce the observations, instabilities may cause the flow to become turbulent, and that this laminar treatment is not strictly valid.

Bornmann, P. L.↗
NASA NTRS1991

Interrelation of soft and hard X-ray emissions during solar flares. II - Simulation model

Two-dimensional electrostatic particle simulations are presented which incorporate the effect of quasi-static electric fields on particle dynamics as well as effects associated with wave-particle interactions induced by the accelerated particles. The properties of the soft and hard X-ray and microwave emissions from such systems are examined. In particular, it is shown that acceleration by quasi-static electric fields and heating via wave-particle interactions produces electron distributions with a broken-power law, similar to those inferred from hard X-ray spectra. Also, heating of the ambient plasma gives rise to a region of hot plasma propagating down to the chromosphere at about the ion sound speed.

Winglee, R. M.↗
NASA NTRS1990

Limits to derived flare properties using estimates for the background fluxes - Examples from GOES

A method has been presented for restricting the random derived flare temperatures and emission measures. The method is based on three tests and is applicable not only to disk-integrated observations, but also for any high-resolution observations that cannot distinguish the emissions from flaring and nonflaring plasma. The first two tests are based on the assumption that both the temperature and the emission measure should increase as the flare flux rises. The third assumes that the preflare temperature of the plasma that flares should exceed the temperature averaged over all other emitting sources. These tests were applied to two solar flares to illustrate the improvements in the derived flare properties. It is shown that flare properties do not always lie between those derived by the use or subtraction of the total preflare flux. The flare properties can, however, be bounded by subtracting and using the long- and short-wavelength preflare fluxes, respectively.

Bornmann, P. L.↗
NASA NTRS1987

Turbulence as a contributor to intermediate energy storage during solar flares

Turbulence is considered as a method for converting the energy observed as mass motions during the impulsive phase into thermal energy observed during the gradual phase of solar flares. The kinetic energy of the large-scale eddies driven by the upflowing material continuously cascades to smaller scale eddies until viscosity is able to convert it into thermal energy. The general properties of steady state, homogeneous, fluid turbulence is a nonmagnetic plasma and the properties of turbulent decay are reviewed. The time-dependent behavior of the velocities and energies observed by the X-Ray Polychromator (XRP) instrument on the SMM during the November 5, 1980 flare are compared with the properties of turbulence. This study indicates that turbulence may play a role in flare energies and may account for a fraction of the total amount of thermal energy observed during the gradual phase. The rate at which the observed flare velocities decrease is consistent with the decay of turbulent energy but may be too rapid to account for the entire time delay between the impulsive and gradual phases.

Bornmann, P. L.↗
NASA NTRS1986

Flare energetics

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.

Wu, S. T.↗
NASA NTRS1986

The energetics of the gradual phase

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.

Strong, K. T.↗
NASA NTRS1985

A new method for determining temperature and emission measure during solar flares from light curves of soft X-ray line fluxes

A method for using the shapes of the light curves of soft X-ray line fluxes observed during the decay phase of solar flares to infer the temperature and emission measure with time is described. Light curves of the November 5, 1980 flare and several additional flares that exhibit breaks are presented, and possible causes for these breaks are discussed. Numerical models that incorporate the effects of temperature changes on the emissivity function are examined, and the model calculations are compared with the line fluxes observed during the November 5, 1980 flare. The model results are used to derive other properties of the flare.

Bornmann, P. L.↗
NASA NTRS1983

Coordinated Einstein and IUE observations of a disparitions brusques type flare event and quiescent emission from Proxima Centauri

The Einstein Imaging Particle Counter observed a major X-ray flare in its entirety during a 5-hr period of simultaneous observations, with the IUE, of the dM5e flare star Proxima Centauri in August, 1980. The detailed X-ray light curve, temperature determinations during various intervals, and UV line fluxes obtained before, during, and after the flare indirectly indicate a 'two-ribbon flare' prominence eruption. The calculated ratio of coronal to bolometric luminosity for the event is about 100 times the solar ratio. The Proxima Cen corona is analyzed in the context of static loop models, in light of which it is concluded that less than 6% of the stellar surface seems to be covered by X-ray emitting active regions.

Haisch, B. M.↗
NASA NTRS1982

Outer atmospheres of cool stars. XII - A survey of IUE ultraviolet emission line spectra of cool dwarf stars

Quantitative information is obtained on the chromospheres and transition regions of M dwarf stars, in order to determine how the outer atmospheres of dMe stars differ from dM stars and how they compare with the outer atmospheres of quiet and active G and K type dwarfs. IUE spectra of six dMe and four dM stars, together with ground-based photometry and spectroscopy of the Balmer and Ca II H and K lines, show no evidence of flares. It is concluded, regarding the quiescent behavior of these stars, that emission-line spectra resemble that of the sun and contain emission lines formed in regions with 4000-20,000 K temperatures that are presumably analogous to the solar chromosphere, as well as regions with temperatures of 20,000-200,000 K that are presumably analogous to the solar transition region. Emission-line surface fluxes are proportional to the emission measure over the range of temperatures at which the lines are formed.

Linsky, J. L.↗