AN ‘EXTENDED SOLAR CYCLE’ AS OBSERVED IN Fe XIV
- Cite this article as:
- Altrock, R.C. Solar Physics (1997) 170: 411. doi:10.1023/A:1004958900477
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Investigation of the behavior of coronal intensity above the limb in Fexiv emission (530.3 nm) obtained at the National Solar Observatory at Sacramento Peak over the last 23 years has resulted in the confirmation of a second set of zones of solar activity at high latitudes, separate from the Main Activity Zones (MAZ). Localized high-latitude intensity maxima, which I will call High-latitude Emission Features (HEF), are observed at 0.15 solar radii above the limb throughout the solar cycle. They persist long enough at a given latitude to be visible in long-term (e.g., annual) averages. I identify two types of HEF. Poleward-moving HEF, which may be identified with the ‘Rush to the Poles’ phenomenon seen in polar-crown prominences, were first seen to appear in this investigation near latitude 60° in 1978. In 1979 equatorward-moving HEF branched off from the poleward-moving HEF (which continued on to reach the pole in 1980) at a latitude of 70° to 80°. They evolved approximately parallel to the MAZ. Near solar minimum, these HEF evolved into the MAZ of cycle 22, and the emission continues its path towards the equator, where it should disappear soon.
Currently, it is clear that the pattern seen earlier is repeating. The poleward-moving HEF became apparent near the beginning of 1988 near 50° to 60° latitude. The northern poleward-moving HEF reached the pole and disappeared in 1990. The southern poleward-moving HEF moved more slowly, reaching the pole and disappearing in 1991. The equatorward-moving HEF that are the precursors of cycle 23 appeared in 1989 to 1990 and began to move approximately parallel to the MAZ of cycle 22. Based on inferences from previous cycles, we can expect these HEF to continue to the equator, with emission ceasing there near 2009. These recent observations increase the evidence for an ‘extended’ solar cycle that begins every 11 years but lasts for approximately 19–20 years.