Global solar corona revealed by time series observations

Time series observations at UV (Extreme Ultraviolet Imaging Telescope/Solar and Heliospheric Observatory) and X-ray (Soft X-Ray Telescope/Yohkoh) wavelengths reveal properties of the global solar corona that are not easily identified in a single image. A median-filtering technique that rejects features varying with time is used to isolate background corona. The coronal hole boundaries, polar plumes, and polar rays in the inner corona are clearly seen in Extreme Ultraviolet Imaging Telescope data over 5 months during the last solar minimum (1996 January through May). For the first time, we provide physical evidence for coronal hole boundaries in the inner corona. The observations show clearly that the polar coronal holes expand divergently with height. A simple latitudinal and radial electron density distribution for the inner corona is found.