Evolution of coronal streamer structure during the rising phase of solar cycle 23

Abstract

White‐light images of the outer corona recorded with the Large Angle Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory ( SOHO ) show a rapid widening of the streamer belt during 1998 and early 1999. The observed streamer structure and its evolution from rotation to rotation are reproduced with a model in which the Thomson‐scattering electrons are concentrated within a narrow layer centered around the heliospheric current sheet. The latitudinal spreading of the streamer belt is shown to be a consequence of the increased rate of magnetic flux emergence in the sunspot latitudes, which led to a weakening of the Sun's axisymmetric dipole moment, to a rapid growth in the nonaxisymmetric components of the coronal field, and hence to a strong tilting and warping of the plasma/current sheet.