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Forecasting the Maxima of Solar Cycle 24 with Coronal Fe xiv Emission
Richard C. Altrock
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 degrees ±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 degrees ±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 degress per year was found in the north, compared to an average of 9.4 ±1.7 degrees per year in the previous cycles. An early fit to the Rush would have reached 76 dgrees at 2014.6. However, in 2010 the slope increased to 7.5 degrees per year (an increase did not occur in the previous three cycles). Extending that rate to 76 degrees ±2 degrees 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 degrees in the south at 2014.2. In 1999, persistent Fe xiv coronal emission known as the “extended solar cycle” appeared near 70 degrees; 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 degrees in the North and 24 degrees in the South. This indicates that solar maximum is occurring now in the North but not yet in the South.
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