Search Publications
Time-Distance Inversion Methods and Results - (Invited Review)
Kosovichev, A. G.; Scherrer, P. H.; Duvall, T. L. _Jr., Jr.
The current interpretations of the travel-time measurements in quiet and active regions on the Sun are discussed. These interpretations are based on various approximations to the 3-D wave equation such as the Fermat principle for acoustic rays and the Born approximation. The ray approximation and its modifications have provided the first view of t…
A comparison of differential rotation measurements - (Invited Review)
Beck, John G.
Observers have long measured solar rotation with different techniques and obtained different results. This paper compares differential rotation measurements from four techniques: Doppler shift, Doppler feature tracking, magnetic feature tracking, and p-mode splittings. The different rotation rates measured by the first three techniques are interpr…
Basic Principles of Solar Acoustic Holography - (Invited Review)
Braun, D. C.; Lindsey, C.
We summarize the basic principles of holographic seismic imaging of the solar interior, drawing on familiar principles in optics and parallels with standard optical holography. Computational seismic holography is accomplished by the phase-coherent wave-mechanical reconstruction of the p-mode acoustic field into the solar interior based on heliosei…
Time-Distance Helioseismology with f Modes as a Method for Measurement of Near-Surface Flows
Duvall, T. L., Jr.; Gizon, L.
Travel times measured for the f mode have been used to study flows near the solar surface in conjunction with simultaneous measurements of the magnetic field. Previous flow measurements of Doppler surface rotation, small magnetic feature rotation, supergranular pattern rotation, and surface meridional circulation have been confirmed. In addition, …
Supra-arcade Downflows in Long-Duration Solar Flare Events
McKenzie, D. E.
This report seeks to introduce the reader to a set of observations made during the decay phase of long-duration event (LDE) flares on the Sun. In a number of events, the soft X-ray images from Yohkoh SXT indicate a downward-directed flow field in the region immediately above the flare arcade. The prototypical event is the M5 flare of 20 January 19…
The Photospheric Convection Spectrum
Raymond, J.; Hathaway, D. H.; Bogart, R. S. +5 more
Spectra of the cellular photospheric flows are determined from observations acquired by the MDI instrument on the SOHO spacecraft. Spherical harmonic spectra are obtained from the full-disk observations. Fourier spectra are obtained from the high-resolution observations. The p-mode oscillation signal and instrumental artifacts are reduced by tempo…
Simultaneous SOHO and Ground-Based Observations of a Large Eruptive Prominence and Coronal Mass Ejection
Heinzel, P.; Plunkett, S. P.; Wu, S. T. +6 more
Coronal mass ejections (CMEs) are frequently associated with erupting prominences near the solar surface. A spectacular eruption of the southern polar crown prominence was observed on 2June 1998, accompanied by a CME that was well-observed by the LASCO coronagraphs on SOHO. The prominence was observed in its quiescent state and was followed throug…
Solar shear flows deduced from helioseismic dense-pack samplings of ring diagrams
Thompson, M. J.; Hill, F.; Toomre, J. +3 more
We report on large-scale horizontal flows in the solar convection zone and their variability in time and space using a local-helioseismology technique known as ring-diagram analysis. By performing this analysis on a dense mosaic of individual regions on the solar disk, i.e., a `Dense-Pack' sampling, and repeating the analysis periodically on sever…
Travel Time Sensitivity Kernels
Kosovichev, A. G.; Birch, A. C.
We derive, following the standard first Born approximation approach used in the geophysics literature, an expression for the travel time perturbation caused by a perturbation to sound speed. In our simple model we employ a point source at one point and calculate the time taken for a wave packet created at the source to move to a second point. In t…
Phase-sensitive Holography of Solar Activity
Braun, D. C.; Lindsey, C.
Phase-correlation statistics comparing acoustic radiation coming out of a particular point on the solar photosphere with acoustic radiation going into it show considerably reduced sound travel times through the subphotospheres of active regions. We have now applied techniques in phase-sensitive seismic holography to data from the Solar Oscillation…