The Origin of Polar Streamers in the Solar Corona

We investigate the large-scale three-dimensional (3D) structure of the solar corona near the maximum of the 23rd solar cycle in an attempt to determine the origin of polar streamers. We use a model that allows us to simulate the quasi-stationary configuration of the large-scale coronal density distribution. The coronal neutral line, as given by the potential field source surface (PFSS) model, serves as a proxy for mid- and low-latitude current sheets. We investigate the contribution of possible polar coronal current sheets associated with large-scale photospheric magnetic neutral lines around the poles of the Sun (polar crown neutral lines). Positions of polar neutral lines are radially extrapolated outward to obtain the configuration of polar current sheets. Coronal plasma sheets are centered around introduced current sheets. Streamer positions during Carrington rotation 1965, near the activity maximum, are calculated. Simulated synoptic maps of the coronal brightness are compared with those obtained from observations by the LASCO C2 coronagraph on board the SOHO spacecraft. We demonstrate that polar streamers are "classical" streamers situated above low-lying loops (observed by SOHO EIT) connecting the regions of opposite magnetic polarity on two sides of polar crown neutral lines. Polar streamer configurations obtained from our model are close to those observed by LASCO. Our results suggest that the PFSS model cannot adequately describe the configuration of streamers during the epoch of high solar activity. The representation of the streamer belt as a single tilted and warped current sheet becomes questionable. Multiple coronal current sheets may better correspond to the observed streamer configurations.