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) wave lengths reveal properties of the global solar corona that are not easily id entified in a single image. A median-filtering technique that rejects featu res varying with time is used to isolate background corona. The coronal hol e 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 prov ide physical evidence for coronal hole boundaries in the inner corona. The observations show clearly that the polar coronal holes expand divergently w ith height. A simple latitudinal and radial electron density distribution f or the inner corona is found.