Solar coronal structure: A comparison of NSO/SP ground-based coronal emission line intensities and temperatures with Yohkoh SXT and WSO magnetic data

Abstract

The large-scale structure of the solar corona is investigated using synoptic maps produced from Fe XIV (530.3 nm), Fe X (637.4 nm) and Ca XV (569.4 nm) data obtained at NSO/SP, Yohkoh/SXT X-ray data and Wilcox Solar Observatory (WSO) ‘source surface’ maps. We find that the Fe XIV data are an excellent proxy for spatially-averaged Yohkoh/SXT data. Isolated emission features and large-scale structures are nearly identical in SXT and Fe XIV maps. In addition, coronal holes and other low-emission regions are very similar. Synoptic temperature maps, calculated from the Fe X Fe XIV ratio, show a tendency for the highest temperatures to occur where the large-scale magnetic fields change polarity at high latitudes (cf. /1/), while lower-latitude features, including active regions, have lower apparent temperatures. Regions of enhanced temperature generally follow the heliospheric current sheet (HCS) as defined by the WSO maps. Further, emission in Ca XV (formet at T ≈ 3 MK), generally occurs only over low-latitude regions that are bright in both Fe X ( T ≈ 1 MK) and Fe XIV ( T ≈ 2 MK). Thus, there is evidence for low (≈1 MK), moderate (≈2 MK) and high (≈3 MK) temperatures in close proximity in the low corona.