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Measurements of Flow Speeds in the Corona Between 2 and 30 R⊙
Llebaria, A.; St. Cyr, O. C.; Michels, D. J. +16 more
Time-lapse sequences of white-light images, obtained during sunspot minimum conditions in 1996 by the Large Angle Spectrometric Coronagraph on the Solar and Heliospheric Observatory, give the impression of a continuous outflow of material in the streamer belt, as if we were observing Thomson scattering from inhomogeneities in the solar wind. Pursu…
Sustaining the Quiet Photospheric Network: The Balance of Flux Emergence, Fragmentation, Merging, and Cancellation
Shine, Richard A.; Title, Alan M.; Schrijver, Carolus J. +2 more
The magnetic field in the solar photosphere evolves as flux concentrations fragment in response to sheared flows, merge when they collide with others of equal polarity, or (partially) cancel against concentrations of opposite polarity. Newly emerging flux replaces the canceled flux. We present a quantitative statistical model that is consistent wi…
Evidence of an Erupting Magnetic Flux Rope: LASCO Coronal Mass Ejection of 1997 April 13
St. Cyr, O. C.; Paswaters, S. E.; Simnett, G. M. +7 more
A coronal mass ejection (CME) observed by LASCO exhibits evidence that its magnetic field geometry is that of a flux rope. The dynamical properties throughout the fields of view of C2 and C3 telescopes are examined. The results are compared with theoretical predictions based on a model of solar flux ropes. It is shown that the LASCO observations a…
Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind
Romoli, M.; Poletto, G.; Noci, G. +2 more
Recent Ultraviolet Coronagraph Spectrometer (UVCS) white-light channel (WLC) observations on board the Solar and Heliospheric Observatory (SOHO) indicate quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes. This is the first observation of possible signatures of compressional waves high above the limb (at heliocen…
Origins of the Slow and the Ubiquitous Fast Solar Wind
Fineschi, S.; O'Neal, R.; Kohl, J. +4 more
We present in this Letter the first coordinated radio occultation measurements and ultraviolet observations of the inner corona below 5.5Rs, obtained during the Galileo solar conjunction in 1997 January, to establish the origin of the slow solar wind. Limits on the flow speed are derived from the Doppler dimming of the resonantly scatte…
Origin and Evolution of Coronal Streamer Structure During the 1996 Minimum Activity Phase
Llebaria, A.; Michels, D. J.; Paswaters, S. E. +17 more
We employ coronal extrapolations of solar magnetograph data to interpret observations of the white-light streamer structure made with the LASCO coronagraph in 1996. The topological appearance of the streamer belt during the present minimum activity phase is well described by a model in which the Thomson-scattering electrons are concentrated around…
Detection of Zonal Shear Flows beneath the Sun's Surface from f-Mode Frequency Splitting
Kosovichev, A. G.; Schou, J.
We report on the first successful measure of the zonal variations of the Sun's differential rotation (so-called torsional oscillations) by helioseismology. Using new helioseismic data from the Michelson Doppler Imager on board SOHO, we have detected zonal flow bands with velocity variation of 5 m s-1 at a depth of 2-9 Mm beneath the sur…
SUMER Observations Confirm the Dynamic Nature of the Quiet Solar Outer Atmosphere: The Internetwork Chromosphere
Judge, P. G.; Wilhelm, K.; Carlsson, Mats
On 1996 March 12, during the commissioning phase of the SOHO mission, we obtained observations of the quiet-Sun with the SUMER instrument. The observations were sequences of 15-20 s exposures of ultraviolet emission-line profiles and of the neighboring continua. These data contain signatures of the dynamics of the solar chromosphere that are uniqu…
Electron Densities in the Solar Polar Coronal Holes from Density-Sensitive Line Ratios of Si VIII and S X
Wilhelm, K.; Schühle, U.; Lemaire, P. +5 more
We derive electron densities as a function of height in the north and south polar coronal holes from a forbidden spectral line ratio of Si VIII. Si VIII is produced at about 8 × 105 K in ionization equilibrium. We also derive densities from a similar line ratio of S X (1.3 × 106 K). The spectra were obtained with the Solar Ul…
Determination of the Sun's Seismic Radius from the SOHO Michelson Doppler Imager
Kosovichev, A. G.; Schou, J.; Dziembowski, W. A. +1 more
Dopplergrams from the Michelson Doppler Imager (MDI) instrument on board the SOHO spacecraft have been used to accurately measure frequencies of the Sun's fundamental (f) mode in the medium angular degree range, l = 88--250. The comparison of these frequencies with the corresponding frequencies of the standard solar models suggests that the appare…