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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…
First Results from the SOHO Ultraviolet Coronagraph Spectrometer
Romoli, M.; Raymond, J. C.; Naletto, G. +23 more
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is being used to observe the extended solar corona from 1.25 to 10 R⊙ from Sun center. Initial observations of polar coronal holes and equatorial streamers are described. The observations include measurements of spectral line profiles for HI Lα and Lβ, Ovi 1032 Å and 1037 Å, Mgx 625 Å, Fexi…
Bi-directional plasma jets produced by magnetic reconnection on the Sun
Inhester, B.; Wilhelm, K.; Innes, D. E. +1 more
Magnetic reconnection, the process by which magnetic lines of force break and rejoin into a lower-energy configuration, is considered to be the fundamental process by which magnetic energy is converted into plasma kinetic energy1. The Sun has a large reservoir of magnetic energy, and the energy released by magnetic reconnection has been…
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…
EIT Observations of the Extreme Ultraviolet Sun
Michels, D. J.; Gurman, J. B.; Berghmans, D. +32 more
The Extreme Ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft has been operational since 2 January 1996. EIT observes the Sun over a 45 x 45 arc min field of view in four emission line groups: Feix, x, Fexii, Fexv, and Heii. A post-launch determination of the instrument flatfield, the instrument scattering function, and the instrume…
First Results of the SUMER Telescope and Spectrometer on SOHO - I. Spectra and Spectroradiometry
Vial, J. -C.; Grewing, M.; Wilhelm, K. +16 more
SUMER - the Solar Ultraviolet Measurements of the Emitted Radiation instrument on the Solar and Heliospheric Observatory (SOHO) - observed its first light on January 24, 1996, and subsequently obtained a detailed spectrum with detector B in the wavelength range from 660 to 1490 Å (in first order) inside and above the limb in the north polar corona…
Composition of Coronal Streamers from the SOHO Ultraviolet Coronagraph Spectrometer
Romoli, M.; Raymond, J. C.; Naletto, G. +24 more
The Ultraviolet Coronagraph Spectrometer on the SOHO satellite covers the 940-1350 Å range as well as the 470-630 Å range in second order. It has detected coronal emission lines of H, N, O, Mg, Al, Si, S, Ar, Ca, Fe, and Ni, particularly in coronal streamers. Resonance scattering of emission lines from the solar disk dominates the intensities of a…
A subsurface flow of material from the Sun's equator to its poles
Scherrer, P. H.; Bogart, R. S.; Duvall, T. L. +1 more
Gas on the Sun's surface has been observed to flow away from the equator towards both poles. If the same flow persists to great depths, it could play an important dynamical role in the eleven-year sunspot cycle, by carrying the magnetic remnants of the sunspots to high latitudes. An even deeper counterflow, which would be required to maintain mass…
Structure and Rotation of the Solar Interior: Initial Results from the MDI Medium-L Program
Kosovichev, A. G.; Hoeksema, J. T.; Scherrer, P. H. +31 more
The medium-l program of the Michelson Doppler Imager instrument on board SOHO provides continuous observations of oscillation modes of angular degree, l, from 0 to ∽ 300. The data for the program are partly processed on board because only about 3% of MDI observations can be transmitted continuously to the ground. The on-board data processing, the …
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…