Forecasting the Maxima of Solar Cycle 24 with Coronal Fe xiv Emission
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The onset of the “Rush to the Poles” of polar-crown prominences and their associated coronal emission is a harbinger of solar maximum. Altrock (Solar Phys. 216, 343, 2003) showed that the “Rush” was well observed at 1.15 R o in the Fe xiv corona at the Sacramento Peak site of the National Solar Observatory prior to the maxima of Cycles 21 to 23. The data show that solar maximum in those cycles occurred when the center line of the Rush reached a critical latitude of 76∘±2∘. Furthermore, in the previous three cycles solar maximum occurred when the highest number of Fe xiv emission features per day (averaged over 365 days and both hemispheres) first reached latitudes 20∘±1.7∘. Applying the above conclusions to Cycle 24 is difficult due to the unusual nature of this cycle. Cycle 24 displays an intermittent Rush that is only well-defined in the northern hemisphere. In 2009 an initial slope of 4.6∘ year−1 was found in the north, compared to an average of 9.4±1.7∘ year−1 in the previous cycles. An early fit to the Rush would have reached 76∘ at 2014.6. However, in 2010 the slope increased to 7.5∘ year−1 (an increase did not occur in the previous three cycles). Extending that rate to 76∘±2∘ indicates that the solar maximum in the northern hemisphere already occurred at 2011.6±0.3. In the southern hemisphere the Rush to the Poles, if it exists, is very poorly defined. A linear fit to several maxima would reach 76∘ in the south at 2014.2. In 1999, persistent Fe xiv coronal emission known as the “extended solar cycle” appeared near 70∘ in the North and began migrating towards the equator at a rate 40 % slower than the previous two solar cycles. However, in 2009 and 2010 an acceleration occurred. Currently the greatest number of emission features is at 21∘ in the North and 24∘ in the South. This indicates that solar maximum is occurring now in the North but not yet in the South.
KeywordsCorona Solar cycle
The observations used herein are the result of a cooperative program of the Air Force Research Laboratory and the National Solar Observatory. I am grateful for the assistance of NSO personnel, especially John Cornett, Timothy Henry, Lou Gilliam, and Wayne Jones, for observing and data-reduction and -analysis services and maintenance of the Evans Solar Facility and its instrumentation and to Raymond N. Smartt, who completely redesigned the Sacramento Peak Photoelectric Coronal Photometer filters in 1982, making it the excellent instrument it is today. I wish to also thank the referee for pointing out several deficiencies in the paper, which I have endeavored to correct.