Temperature Structure of the High-Latitude Corona

Abstract

This Letter explores the physical and morphological characteristics of the large-scale coronal structures such as polar coronal rays and high-latitude streamers as seen in white light and relates these structures to observations in soft X-ray (3-45 A) and red (Fe X λ6374) and green (Fe XIV λ5303) line emissions to estimate their temperatures. Analysis shows that polar rays can be characterized by at least two temperature classes: Cool (0.7-1.3 × 106 K) rays are a dominant feature of the polar corona during the quiescent phase of the solar cycle. The hot (1.8-2.6 × 106 K) rays, when present, form a small subset of the array of rays seen in white light. Hot rays seem to emerge from the boundary of the polar coronal hole (polar crown filament belt). The location of the cool rays, on the other hand, can be on the boundary or inside the coronal hole. We do not always find a one-to-one correspondence between the polar rays observed in white light versus those observed in XUV and visible emission lines. We find the emission-line ratio temperature to be high in the high-latitude (>45°) coronal streamers with enhanced white-light emission. These streamers are located along a neutral line that separates the weak, old-cycle polar field from the weak, new-cycle high-latitude magnetic field of opposite polarity.