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NASA NTRS1984

Separation of large-scale photospheric Doppler patterns

Mount Wilson solar Doppler data covering the period from January 1967 to March 1984 are refit using polynomials appropriate to the rotation, limbshift, and meridional flow motion fields identified by LaBonte and Howard (1982). No 'ear' terms are included, and additional degrees of freedom are allowed in the limbshift and meridional flow fluctions. An examination of the residuals shows this fit to be a slight improvement over that of the above workers, and the new residuals are used to tighten the limits on photospheric giant signatures to about 1 m/s per wavenumber. The focus of the paper is on polynomial functions and their fit-determined coefficients, with particular emphasis on the problem of crosstalk as the coefficients are tracked over time.

Snodgrass, H. B.↗

NASA NTRS1986

A comparison of photospheric electric current and ultraviolet and X-ray emission in a solar active region

This paper presents an extensive set of coordinated observations of a solar active region, taking into account spectroheliograms obtained with the aid of the Solar Maximum Mission (SMM) Ultraviolet Spectrometer Polarimeter (UVSP) instrument, SMM soft X-ray polychromator (XRP) raster maps, and high spatial resolution ultraviolet images of the sun in Lyman-alpha and in the 1600 A continuum. These data span together the upper solar atmosphere from the temperature minimum to the corona. The data are compared to maps of the inferred photospheric electric current derived from the Marshall Space Flight Center (MSFC) vector magnetograph observations. Some empirical correlation is found between regions of inferred electric current density and the brightest features in the ultraviolet continuum and to a lesser extent those seen in Lyman-alpha within an active region.

Haisch, B. M.↗

NASA NTRS1986

Spectral flux from low-density photospheres - Approximate results

Radiative transfer through sharp, quasi-static atmospheres containing mostly hydrogen is considered at densities low enough that scattering dominates absorption and collisional excitations are negligible. It is found that the balance between photoionization and radiative recombination which governs the atomic level populations greatly reduces the effective absorptive opacity. Approximate results for the emergent continuum spectral flux are obtained, significantly different than if local thermodynamic equilibrium level populations were assumed. The flux jumps at the photoionization thresholds are relatively small for the photospheric temperatures T sub p(v) greater than or about 6000 K considered, and T sub p increases toward the far-ultraviolet. It appears that the lack of a Balmer jump in spectra of Type II supernovae implies that the flux is diluted below that of a blackbody at the same color temperature, which increases the value of the Hubble constant obtained by the Baade (1926) method.

Hershkowitz, S.↗

NASA NTRS1985

The cyclical variation of energy flux and photospheric magnetic field strength from coronal holes

The average soft X-ray emission from coronal holes observed on images obtained during rocket flights from 1974 to 1981 is measured. The variation of this emission over the solar cycle was then compared with photospheric magnetic flux measurements within coronal holes over the same period. It was found that coronal hole soft X-ray emission could be detected and that this emission appeared to increase with the rise of the sunspot cycle from activity minimum to maximum. These quantitative results confirmed previous suggestions that the coronal brightness contrast between holes and large-scale structure decreased during this period of the cycle. Gas pressures at the hole base were estimated for assumed temperatures and found to vary from about 0.03 dyne/sq cm in 1974 to 0.35 dyne/sq cm in 1981. The increase in coronal hole X-ray emission was accompanied by a similar trend in the surface magnetic flux of near-equatorial holes between 1975 and 1980 (Harvey et al., 1982).

Webb, D. F.↗

NASA NTRS1986

The detection of photospheric X-ray pulsations from PG 1159-035 with EXOSAT

The detection of soft X-ray pulsations from the hot, helium-rich, degenerate object, PG 1159-035 is reported. These observations, obtained with the Low Energy experiment on EXOSAT, show the presence of large-amplitude soft X-ray (44-150 A) pulsations analogous to several of the low-amplitude, nonradial, g-mode pulsations which are observed in the optical. These soft X-ray pulsations, with periods of 516 s, 524 s, and 539 s, arise from the photosphere of PG 1159-035 and constitute the first observations of stellar atmospheric pulsational phenomena in the X-ray band.

Barstow, M. A.↗

NASA NTRS1986

Filament formation due to photospheric shear

Recently, Wu et al. (1983, 1986) developed a three-dimensional, time-dependent axisymmetric ideal magnetohydrodynamic (MHD) model which has been used to study lower solar atmospheric response due to photospheric motion. They have shown that various observed solar features can be formed from these numerical simulation experiments. Some work currently in progress which has resulted from a specific numerical simulation experiment is reported. These results may elucidate the possible physical mechanism of formation of filament.

Wu, S. T.↗

NASA NTRS1986

The white light corona and photospheric magnetic fields

Some results are presented from a continuing investigation of the coronal structure vs. the photospheric magnetic field relationship. Two approaches to the problem are considered. First, the individual coronal features recorded at each limb were located on a chart of the magnetic field measured with low spatial resolution, depicting the large scale or global field configuration. Second, the characteristics of neutral line segments, defined by the presence of H alpha line filament, with no associated coronal structure were investigated. Preliminary results are discussed.

Mccabe, Marie K.↗

NASA NTRS1987

Exploration of the solar-stellar connection at high spectral resolution with the Ultraviolet Spectrometer and Polarimeter, and studies of thermal bifurcation at the photosphere-chromosphere interface

The dynamics of high-excitation plasma in the 100,000 K transition zones of stars of late spectral type, as observed with the International Ultraviolet Explorer, was compared with the radial gas velocities of individual structural features of the solar TZ, as observed with high spatial resolution by the UVSP on the Solar Maximum Mission. The 4th-positive system of carbon monoxide in the quiet sun and in active regions was studied in order to explore the properties of thermal inhomogeneities at the critical interface between the photosphere and chromosphere.

Source record↗

NASA NTRS1987

Spherical harmonic analysis of steady photospheric flows

A technique is presented in which full disk Doppler velocity measurements are analyzed using spherical harmonic functions to determine the characteristics of the spectrum of spherical harmonic modes and the nature of steady photospheric flows. Synthetic data are constructed in order to test the technique. In spite of the mode mixing due to the lack of information about the motions on the backside of the sun, solar rotation and differential rotation can be accurately measured and monitored for secular changes, and meridional circulations with small amplitudes can be measured. Furthermore, limb shift measurements can be accurately obtained, and supergranules can be fully resolved and separated from giant cells by their spatial characteristics.

Hathaway, David H.↗

NASA NTRS1987

Periodic photospheric and chromospheric modulation in Alpha Orionis (Betelgeuse)

The bright cool supergiant Alpha Orionis has been monitored spectroscopically and photometrically over the past three years (1984-1986) in the optical and the ultraviolet wavelength regions. A 420-day periodic modulation of the flux is observed in the optical and ultaviolet continua, and in the Mg II line emission cores. Periodic photospheric pulsations are the most likely explanation of these observations. This identification is based on the large amplitude of the variation, the correlation of the continuum and chromospheric fluxes, and the length of the observed period. Pulsation may heat and extend the atmosphere of Alpha Ori and initiate the mass flow from the star.

Dupree, A. K.↗

NASA NTRS1987

Spectral flux from low-density photospheres - Low-temperature results

Previous studies of low-density, hydrogen-dominated, quasi-static photospheres (such as those of Type II supernovae) are extended to effective temperatures Te = 4000-6000 K. These temperatures include those at which hydrogen recombines at the densities investigated, corresponding to scale heights Delta R = (1-100) x 10 to the 14th cm. In addition to presenting results for the emergent spectral flux (required to obtain supernova distances via the Baade method), the validity of some assumptions previously made is demonstrated. It is shown that the level populations of hydrogen are governed solely by a balance between photoionization directly to and recombination directly from the continuum.

Hershkowitz, Stephen↗

NASA NTRS1987

The resistances of the photosphere and of a flaring coronal loop

Two aspects of solar flares are considered from the point of view of circuit theory. First, it is shown that the so-called 'dynamo models', which invoke an analogy between the earth's magnetosphere-ionosphere circuit and the solar corona-photosphere circuit, are ill-founded. Second, the rate of coronal energy release in the impulsive phase of a modest flare is considered, and it is shown that, if the energy going into mass motion can be neglected, the corona must present a resistance of about 0.001 ohm. Classical resistivity, even in a highly filamented circuit, cannot provide so high a resistance. Anomalous resistivity due to ion sound turbulence can provide the required resistance in this case, but is insufficient to explain the very high power levels inferred in some fast spikes.

Melrose, D. B.↗

NASA NTRS1987

A spherical harmonic decomposition technique for analysing steady photospheric flows

Steady flows in the photosphere, including differential rotation, meridional circulation and convection, can be represented by a spectrum of modes. A technique is described in which the spherical harmonic functions are used to determine the characteristics of this spectrum and the nature of these flows. Some information about the spectrum is lost because only one hemisphere is seen, only the line of sight velocity is measured and the measurements contain noise. This produces an apparent mixing between spectral modes. By analyzing synthetic data it is found that, in spite of this mixing, differential rotation can be accurately measured, meridional circulations with small amplitudes can be extracted from the data and giant cells might be separated from supergranules.

Hathaway, David H.↗

NASA NTRS1988

Temporal filters for isolating steady photospheric flows

A variety of temporal filters are tested on artificial data with 60 and 75 s sampling intervals to determine their accuracy in separating the nearly-steady photospheric flows from the p-mode oscillations in Doppler velocity data. Longer temporal averages are better at reducing the residual signal due to p-modes but they introduce additional errors from the rotation of the supergranule pattern across the solar disk. Unweighted filters (boxcar averages) leave residual rms errors of about 6 m/s from the p-modes after 60 min of averaging. Weighted filters, with nearly Gaussian shapes, leave similar residual errors after only 20 min of averaging and introduce smaller errors from the rotation of the supergranule pattern. The best filters found are weighted filters that use data separated by 150 or 120 s so that the p-modes are sampled at opposite phases.

Hathaway, David H.↗

NASA NTRS1988

Coronal magnetic fields produced by photospheric shear

The magnetofrictional method for computing force-free fields is used to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It is found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear amplitude, by a simple functional form. The fit parameters depend only on the distribution of normal field in the photosphere and the form of the shearing displacement. They show that the energy is relatively more enhanced if the shear occurs: (1) where the normal field is strongest; and/or (2) in the inner region of the dipole, near the axis; and/or (3) over a large fraction of the dipole area.

Klimchuk, J. A.↗

NASA NTRS1988

Simulating photospheric Doppler velocity fields

A method is described for constructing artificial data that realistically simulate photospheric velocity fields. The velocity fields include rotation, differential rotation, meridional circulation, giant cell convection, supergranulation, convective limb shift, p-mode oscillations, and observer motion. Data constructed by this method can be used for testing algorithms designed to extract and analyze these velocity fields in real Doppler velocity data.

Hathaway, David H.↗

NASA NTRS1989

Determination of solar flare accelerated ion angular distributions from SMM gamma ray and neutron measurements and determination of the He-3/H ratio in the solar photosphere from SMM gamma ray measurements

Comparisons of Solar Maximum Mission (SMM) observations of gamma-ray line and neutron emission with theoretical calculation of their expected production by flare accelerated ion interactions in the solar atmosphere have led to significant advances in the understanding of solar flare particle acceleration and interaction, as well as the flare process itself. These comparisons have enabled the determination of, not only the total number and energy spectrum of accelerated ions trapped at the sun, but also the ion angular distribution as they interact in the solar atmosphere. The Monte Carlo program was modified to include in the calculations of ion trajectories the effects of both mirroring in converging magnetic fields and of pitch angle scattering. Comparing the results of these calculations with the SMM observations, not only the angular distribution of the interacting ions can be determined, but also the initial angular distribution of the ions at acceleration. The reliable determination of the solar photospheric He-3 abundance is of great importance for understanding nucleosynthesis in the early universe and its implications for cosmology, as well as for the study of the evolution of the sun. It is also essential for the determinations of the spectrum and total number of flare accelerated ions from the SMM/GRS gamma-ray line measurements. Systematic Monte Carlo calculations of the time dependence were made as a function of the He-3 abundance and other variables. A new series of calculations were compared for the time-dependent flux of 2.223 MeV neutron capture line emission and the ratio of the time-integrated flux in the 2.223 MeV line to that in the 4.1 to 6.4 MeV nuclear deexcitation band.

Lingenfelter, Richard E.↗

NASA NTRS1990

Dynamic Power Spectral Analysis of Solar Measurements from Photospheric, Chromospheric, and Coronal Sources

An important aspect in the power spectral analysis of solar variability is the quasistationary and quasiperiodic nature of solar periodicities. In other words, the frequency, phase, and amplitude of solar periodicities vary on time scales ranging from active region lifetimes to solar cycle time scales. Here, researchers employ a dynamic, or running, power spectral density analysis to determine many periodicities and their time-varying nature in the projected area of active sunspot groups (S sub act). The Solar Maximum Mission/Active Cavity Radiometer Irradiance Monitor (SMM/ACRIM) total solar irradiance (S), the Nimbus-7 MgII center-to-wing ratio (R (MgII sub c/w)), the Ottawa 10.7 cm flux (F sub 10.7), and the GOES background x ray flux (X sub b) for the maximum, descending, and minimum portions of solar cycle 21 (i.e., 1980 to 1986) are used. The technique dramatically illustrates several previously unrecognized periodicities. For example, a relatively stable period at about 51 days has been found in those indices which are related to emerging magnetic fields. The majority of solar periodicities, particularly around 27, 150 and 300 days, are quasiperiodic because they vary in amplitude and frequency throughout the solar cycle. Finally, it is shown that there are clear differences between the power spectral densities of solar measurements from photospheric, chromospheric, and coronal sources.

Bouwer, S. D.↗