Showing papers by "Bruce W. Lites published in 1985"
TL;DR: In this article, the velocity power spectrum in one spectral line formed in the low photosphere and in another formed in low chromosphere, just above the temperature minimum, was found to exhibit both 5-min and 3-min oscillations, with the kinetic energy of the latter being at least 5 times greater in the lower photosphere than in the higher chromosphere.
Abstract: In the present simultaneous measurement of sunspot umbrae velocity oscillations in one spectral line formed in the low photosphere, and in another formed in the low chromosphere, just above the temperature minimum, the velocity power spectrum in each is found to exhibit both 5-min and 3-min oscillations, with the kinetic energy of the latter being at least 5 times greater in the low photosphere than in the low chromosphere. The 3-min umbral oscillation has the character of a coherent, vertically standing wave in the photosphere. These results imply a photospheric, rather than chromospheric, resonant origin for the fundamental 3-min umbral oscillation. A negative phase difference at frequencies around 2 mHz suggests the presence of gravity waves in the umbra.
60 citations
Journal Article•
49 citations
TL;DR: In this article, the authors show that the He i 10830 A line gives reliable Doppler shift measurements in the upper chromosphere above active regions, and that it shows a strong correlation with the line-of-sight velocity images in certain regions of some active regions.
Abstract: We show that the He i 10830 A line gives reliable Doppler shift measurements in the upper chromosphere above active regions. Persistent flow patterns in active regions observed near the solar limb show features previously noted in Dopplergrams using the Civ transition region ultraviolet emission line. Unlike the Civ measurements, however, the He i absorption shows a strong correlation with the line-of-sight velocity images in certain regions of some active regions.
14 citations
01 Jan 1985
TL;DR: In this paper, the authors cast each line and continuum transition into an equivalent two-level form, consisting of a scattering and a source term, and show that the behavior of these terms with height immediately reveals how the line excitation is driven.
Abstract: Efficient methods are now available for solving multi - level, multi-transition non-LTE transfer problems in stellar atmospheres in the approximation of complete redistribution. Once such a solution is obtained, however, it is frequently desirable to know more about the solution than simply the emergent intensity or the flux. We present a means by which one may easily understand how all the line and continuum transitions are formed. We cast each transition into an equivalent two-level form, consisting of a scattering and a source term. The behavior of these terms with height immediately reveals how the line excitation is driven. Numerical perturbations of the atomic rates, both collisional and radiative, about this solution reveal the sensitivity of the scattering and source terms to various atomic rate and helps one to identify the other interlocking radiative and collisional transitions important to the formation of a spectral line. We demonstrate this method through application to the formation of the solar hydrogen lines and the Lyman continuum.
2 citations