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R.C. Altrock (Air Force Research Lab., NSO at Sacramento Peak)
Prediction of the exact time of solar maximum is a matter of disagreement among solar scientists and of some importance to satellite operators, space-system designers, etc. Most predictions are based on physical conditions occurring at or before the long-term minimum of activity preceding the maximum in question. However, a perhaps-more-reliable indicator of the timing of the maximum occurs early in the rise phase of the solar cycle. A study of the long-term variation of coronal emission features in Fe XIV from the National Solar Observatory at Sacramento Peak has shown that, prior to solar maximum, emission features appear near 55 degrees latitude in both hemispheres and begin to move towards the poles at a rate of 9 to 13 degrees of latitude per year. This motion is maintained for a period of 3 or 4 years, at which time the emission features disappear near the poles. This phenomenon has been referred to as the "Rush to the Poles". The maximum of solar activity historically occurs approximately 16 +/- 1 months before the features reach the poles. In 1997, Fe XIV emission features appeared near 55 degrees latitude, and subsequent observations have shown that these features are moving towards the poles. This then is the Rush to the Poles observed in previous solar cycles. Based on observations up through October 1998 over three cycles, these features will reach the poles in approximately October 2000, which results in a prediction for solar maximum of between June and August 1999, substantially earlier than many other predictions. A maximum smoothed sunspot number of approximately 160 is inferred from the similarity of the rate of progression towards the poles in this cycle compared to the two previous cycles. The current status of Rush to the Poles and of the solar cycle will be reviewed and conclusions drawn about the reliability of this method.
This work was supported by the Air Force Office of Scientific Research.
If the author provided an email address or URL for general inquiries, it is a
s follows:
http://www.sunspot.noao.edu/~altrock