Report on the solar physics-plasma physics workshop

This report summarizes the proceedings of a meeting held on 17–20 September 1974, at Stanford University. The purpose was to explore plasma physics problems which arise in the study of solar physics. Sessions were concerned with specific questions including the following: Is the solar plasma thermal or non-thermal? What spectroscopic data are required? What types of magnetic field structures exist? Do MHD instabilities occur? Do resistive or non-MHD instabilities occur? What mechanisms of particle acceleration have been proposed? What information do we have concerning shock waves? Very few questions were answered categorically but, for each question, there was discussion concerning the observational evidence, theoretical analyses, and existing or potential laboratory and numerical experiments.     

Spatial structure in lines in the 3398–3526 å region at the extreme limb: Observation,identification and interpretation

We have obtained spectrograms of high spatial and spectral resolution of the extreme solar limb, using the vacuum tower telescope of Sacramento Peak Observatory. We have identified emission lines in the range 3398–3526 Å, and classified them according to intensity, spatial structure (intensity variation), and profile. Some lines show spatial intensity variation; others do not. We show that this effect is related to the abundance of the element responsible for the line and the mean lower-level excitation potential of interlocked lines. We explain the effect in terms of radiative interlocking with other lines, as well as the characteristic size of the volume contributing to the mean intensity.Also Five College Astronomy Department, Amherst, Mass. 01003, U.S.A.Operated by the Association of Universities for Research in Astronomy Inc. under contract with the National Science Foundation.     

The interpretation of velocity filtergrams

The paper describes a numerical experiment in which the effect of an assumed velocity distribution in the solar atmosphere on the intensity difference between a blue- and a red-wing filter-gram is derived. This results in the effective optical depth at which the velocity is measured. It is shown that this _eff strongly depends on the assumed velocity distribution.     

The rotational motion of an earth orbiting gyroscope according to the Einstein theory of general relativity

The classical Poisson equations of rotational motion are used to study the attitude motions of an Earth orbiting, rapidly spinning gyroscope perturbed by the effects of general relativity (Einstein theory). The center of mass of the gyroscope is assumed to move about a rotating oblate Earth in an evolving elliptic orbit which includes all first-order oblateness effects produced by the Earth.A method of averaging is used to obtain a transformation of variables, for the nonresonance case, which significantly simplifies the Poisson differential equations of motion of the gyroscope. Longterm solutions are obtained by an exact analytical integration of the simplified transformed equations. These solutions may be used to predict both the orientation of the gyroscope and the motion of its rotational angular momentum vector as viewed from its center of mass. The results are valid for all eccentricities and all inclinations not near the critical inclination.This paper represents a part of the author's Ph. D. dissertation for the Mathematics Department, Auburn University.     

The intensity,velocity and magnetic structure of a sunspot region

High resolution sunspot photographs in the blue, red and infrared continuum exposed on various days were used to derive the center-to-limb variation of the intensity ratio = I _sp / I _ph. Special care was taken to correct for image blurring, scattered light and the influence of line absorption.The observed increase of specific umbral intensities _u towards the limb leads to an extremely small temperature gradient in the umbra. From geometrical changes of the profiles (Wilson effect), we derived an umbral depression of about 650 km and a density scale height of about 450 km when H ^- is assumed to be the predominant source of absorption. The penumbral depression was found to be 50 km or less. The density scale height of the umbra as computed from the observed temperature distribution is 80 km in the case of hydrostatic equilibrium. We conclude that either magnetic pressure components produce deviations from hydrostatic equilibrium or that another source of absorption, dominating in the outer layers, has to be taken into account.     

A morphological study of solar spicules

From improved spicule filtergrams obtained with the Sacramento Peak vacuum telescope we measured some spicule properties. The spicule diameter of 950 km was well resolved. A small decrease of diameter with height was observed confirming older observations. The expansion of the spicule was found to be at least an order of magnitude less than reported by Mouradian. Spicule counts are very sensitive to the threshold intensity of the observations. Counts, and their dependence on threshold intensity, height and wavelength are reported.On leave from the Astronomy Department, University of Texas, Austin, Texas.