FIRST VIEW OF THE EXTENDED GREEN-LINE EMISSION CORONA AT SOLAR-ACTIVITY MINIMUM USING THE LASCO-C1 CORONAGRAPH ON SOHO

The newly developed C1 coronagraph as part of the Large-Angle Spectros copic Coronagraph (LASCO) on board the SOHO spacecraft has been operat ing since January 29, 1996. We present observations obtained in the fi rst three months of operation. The green-line emission corona can be m ade visible throughout the instrument's full field of view, i.e., from 1.1 R-. out to 3.2 R-. (measured from Sun center). Quantitative evalu ations based on calibrations cannot yet be performed, but some basic s ignatures show up even now: (1) There are often bright and apparently closed loop systems centered at latitudes of 30 degrees to 45 degrees in both hemispheres. Their helmet-like extensions are bent towards the equatorial plane. Farther out, they merge into one large equatorial ' streamer sheet' clearly discernible out to 32 R-.. (2) At mid latitude s a more diffuse pattern is usually visible, well separated from the h igh-latitude loops and with very pronounced variability. (3) All high- latitude structures remain stable on time scales of several days, and no signature of transient disruption of high-latitude streamers was ob served in these early data. (4) Within the first 4 months of observati on, only one single 'fast' feature was observed moving outward at a sp eed of 70 km s(-1) close to the equator. Faster events may have escape d attention because of data gaps. (5) The centers of high-latitude loo ps are usually found at the positions of magnetic neutral lines in pho tospheric magnetograms. The large-scale streamer structure follows the magnetic pattern fairly precisely. Based on our observations we concl ude that the shape and stability of the heliospheric current sheet at Solar activity minimum are probably due to high-latitude streamers rat her than to the near-equatorial activity belt.