HR: 0830h
AN: SH41B-0462    [PDF]
TI: Can SOHO SWAN Detect CMEs?
AU: * St. Cyr, O C
EM: Chris.StCyr@nasa.gov
AF: NASA-Goddard, Code 682, Greenbelt, MD 20771 United States
AU: * St. Cyr, O C
EM: Chris.StCyr@nasa.gov
AF: The Catholic University of America, Department of Physics, Washington, DC 20064 United States
AU: Malayeri, M L
AF: The Catholic University of America, Department of Physics, Washington, DC 20064 United States
AU: Malayeri, M L
AF: University of Maryland, Department of Physics, College Park, MD 20742 United States
AU: Yashiro, S
AF: The Catholic University of America, Department of Physics, Washington, DC 20064 United States
AU: Quemerais, E
AF: CNRS/Service d'Aeronomie, R‚duit de VerriŠres - BP 3 Route des Gatines, VerriŠres-le-Buisson, 91371 France
AU: Bertaux, J
AF: CNRS/Service d'Aeronomie, R‚duit de VerriŠres - BP 3 Route des Gatines, VerriŠres-le-Buisson, 91371 France
AU: Howard, R
AF: Naval Research Laboratory, 4555 Overlook Ave. S.W., Washington, DC 20375 United States
AB: We have investigated the possibility that the Solar Wind Anisotropies (SWAN) remote sensing instrument on SOHO may be able to detect coronal mass ejections (CMEs) in neutral Hydrogen Lyman-$\alpha$ emission. We have identified CMEs near the Sun in observations by the SOHO LASCO white-light coronagraphs and in extreme ultraviolet emissions using SOHO EIT. There are very few methods of tracking CMEs after they leave the coronagraph's field-of-view, so this is an important topic to study. The primary science goal of the SWAN investigation is the measurement of large-scale structures in the solar wind, and these are obtained by detecting intensity fluctuations in Lyman-$\alpha$. SWAN consists of a pair of sensors on opposite panels of SOHO. The instantaneous field-of-view of each sensor unit is a 5$\deg$ x 5$\deg$ square, divided into 1$\deg$ pixels. A gimbaled periscope system allows each sensor to map the intensity distribution of Lyman-$\alpha$, and the entire sky can be scanned in less than one day. This is the typical mode of operation for this instrument (Bertaux et al., Solar Physics, 162, 403-439, 1995). Beginning in May 2002 the sky-scan mode of the SWAN detectors was interrupted, and they were held stationary for one-or-more 15-hour campaigns each week. During those campaigns the SWAN sensors were positioned above the East or West equator of the Sun at locations chosen to be as close to the Sun as possible (typically 50 solar radii from Sun-center). Based on the LASCO and EIT data, we have identified CMEs whose extrapolated height-time measurements indicated that the events would cross the SWAN field during the campaign period. During 12 months' observation, there were $\sim$10 CMEs that met two criteria: (1) an event low in the corona near the solar limb could be unambiguously identified in EIT; and (2) the CME could be tracked beyond 20 R${\sun}$ in LASCO C3. We consider these CMEs to be particularly well-observed since the speed measured in LASCO could be reliably extrapolated to the SWAN field-of-view. We will report preliminary results of this novel observing campaign.
DE: 7513 Coronal mass ejections
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting