, Volume 216, Issue 1-2, pp 343-352

Use of ground-based coronal data to predict the date of solar-cycle maximum

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Prediction of the exact date of the maximum of the 11-year solar activity cycle 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 solar-cycle minimum preceding the maximum in question. However, another indicator of the timing of the maximum occurs early in the rise phase of the solar cycle. A study of the variation over two previous solar cycles 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 above 50° latitude in both hemispheres and begin to move towards the poles at a rate of 8° to 11° 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'. These observations show that the maximum of solar activity, as seen in the sunspot number, occurs approximately 19 ± 2 months before the features reach the poles. In 1997, Fe xiv emission features appeared near 55° latitude, and began to move towards the poles. Using the above historical data from cycles 21 and 22, we will see how the use of progressively more data from cycle 23 affects the prediction of the date of solar maximum. The principal conclusion is that the date of solar maximum for cycle 23 could be predicted to within 6 months as early as 1997. For solar cycle 24, when this phenomenon first becomes apparent later this decade, the average parameters for cycles 21–23 can be used to predict the date of solar maximum.