LARGE-SCALE CORONAL TEMPERATURE AND DENSITY DISTRIBUTIONS, 1984-1992

In this Letter we characterize the temperature and the density structure of the corona utilizing spectrophotometric observations at different heights but at the same latitude during the descending phase of cycle 21 through the ascending phase of cycle 22. The data include ground-based intensity observations of the green (Fe XIV lambda5303) and red (Fe x lambda6374) coronal forbidden lines, photospheric magnetographs from the National Solar Observatory, Kitt Peak, and synoptic maps of white-light K-coronal polarized brightness, pB, from the High Altitude Observatory. A determination of plasma temperature T can be estimated from the intensity ratio Fe x/Fe xiv (where T is inversely proportional to the ratio), since both emission lines come from ionized states of Fe, and the ratio is only weakly dependent on density. Distributions of the electron temperature from the line ratio and the polarized brightness which yields electron density of the corona during the descending and the ascending phases of solar cycles 21 and 22 are presented. These data refer to structures of the corona which are relatively large scale, having a temporal coherence of at least two or more synoptic rotation periods, such as the streamer belts, the individual helmet streamers, and the larger coronal holes. We observe that there is a large-scale organization of the inferred coronal temperature distribution that is associated with the large-scale structures in the solar magnetic fields; this organization tends to persist through most of the magnetic activity cycle. This distribution differs in spatial and temporal characterization from the traditional picture of sunspot and active region evolution over the range of sunspot cycles, which are manifestations of the small-scale, strong magnetic field regions. For example, during 1987-1990 the active region latitudes drift equatorward, whereas bright coronal features in white light and the inferred temperature structures drift poleward.