Evidence of mass outflow in the low corona over a large sunspot
Abstract
An extreme ultraviolet (EUV) imaging spectrograph designed for soundings rocket flight has been used to search for velocity fields in the low solar corona. During a flight in May, 1989, we obtained emission line profile measurements along a chord through an active region on the Sun. Relative Doppler velocities were measured in emissions lines of Mg IX, Fe XV, and Fe XVI with a sensitivity of 2-3 km s-1 at 350 A. The only Doppler shift appreciably greater than this level was observed in the line of Mg IX at 368.1 A over the umbra of the large sunspot. The maximum shift measured at that location corresponded to a velocity toward the observer of 14 +/- 3km s-1 relative to the mean of measurements in that emission line made elsewhere over the active region. The magnetic field in the low corona was aligned to within 10° of the line of sight at the location of maximum Doppler shift. Depending on the magnetic field geometry, this mass outflow could either re-appear as a downflow of material in distant footpoints of closed coronal loops or, if along open field lines, could contribute to the solar wind. The site of the sunspot was near a major photospheric magnetic field boundary. Such boundaries have been associated with low-speed solar wind as observed in interplanetary plasmas.
- Publication:
-
Advances in Space Research
- Pub Date:
- April 1994
- DOI:
- 10.1016/0273-1177(94)90162-7
- Bibcode:
- 1994AdSpR..14d..61N
- Keywords:
-
- Emission Spectra;
- Line Spectra;
- Solar Corona;
- Solar Magnetic Field;
- Solar Spectra;
- Solar Wind;
- Sunspots;
- Doppler Effect;
- Extreme Ultraviolet Radiation;
- Imaging Spectrometers;
- Interplanetary Magnetic Fields;
- Satellite Observation;
- Solar Physics;
- Spaceborne Astronomy;
- SPACE;
- EXPLORATION;
- VENUS;
- PROBES;
- BALLOONS;
- ATMOSPHERE;
- ALTITUDE;
- DESIGN;
- MISSION PLANNING;
- PARAMETERS;
- TECHNICAL ASPECTS;
- TEMPERATURE;
- THERMAL EFFECTS;
- CALCULATIONS;
- ALLOYS;
- TITANIUM;
- EQUIPMENT;
- Astrophysics