Latitudinal and Solar-Cycle Variations of the White-Light Corona from SOHO/LASCO Observations

Abstract

SOHO/LASCO data were used to obtain the latitudinal and radial distributions of the brightness of the K- and F-corona in the period of 1996 - 2007, and their solar-cycle variations were studied. Then an inversion method was employed to obtain the radial distributions of the electron density N_e(R,θ) for various latitude values on the coronal images. Our values of N_e(R,θ) are in good agreement with the findings of other authors. We found that in an edge-on streamer belt the electron density, like the K-corona brightness, varies with distance more slowly in the near-equatorial rays than in near-polar regions. We have developed a method for assessing the maximum values of the electron density at the center of the face-on streamer belt in its bright rays and depressions between them. Not all bright rays observed in the face-on streamer belt are found to be associated with an increased electron density in them. Mechanisms for forming such rays have been suggested.