The solar cycle variation of coronal temperature and density during cycle 21-22

In this paper we characterize the temperature and the density structure of the corona utilizing co-spatial spectrophotometric observations during the descending phase of cycle 21 through the ascending phase of cycle 22. The data include ground-based intensity observations of the green (5303A Fe XIV) and red (6374A Fe X) coronal forbidden lines from Sacramento Peak and synoptic maps of white-light K-coronal polarized brightness, pB from the High Altitude Observatory, and photospheric magnetographs from the National Solar Observatory, Sacramento Peak. A determination of plasma temperature T can be derived unambiguously from the intensity ratio Fe X/Fe XIV, since both emission lines come from ionized states of Fe, and the ratios are only weakly dependent on density. The latitudinal variation of the temperature and the density within the descending and the ascending phases of solar cycle 21 and 22 are presented. There is a large-scale organization of the inferred coronal temperature distribution; these structures tend 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 cycle.