科研之友
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摘要
More than 70 years ago, it was recognised that ionospheric F2-layer critical frequencies [foF2] had a strong relationship to sunspot number. Using historic datasets from the Slough and Washington ionosondes, we evaluate the best statistical fits of foF2 to sunspot numbers (at each Universal Time [UT] separately) in order to search for drifts and abrupt changes in the fit residuals over Solar Cycles 17 - 21. This test is carried out for the original composite of the Wolf/Zurich/International sunspot number [R], the new "backbone" group sunspot number [R-BB], and the proposed "corrected sunspot number" [R-C]. Polynomial fits are made both with and without allowance for the white-light facular area, which has been reported as being associated with cycle-to-cycle changes in the sunspot-number-foF2 relationship. Over the interval studied here, R, R-BB, and R-C largely differ in their allowance for the "Waldmeier discontinuity" around 1945 (the correction factor for which for R, R-BB, and R-C is, respectively, zero, effectively over 20 %, and explicitly 11.6 %). It is shown that for Solar Cycles 18 - 21, all three sunspot data sequences perform well, but that the fit residuals are lowest and most uniform for R-BB. We here use foF2 for those UTs for which R, R-BB, and R-C all give correlations exceeding 0.99 for intervals both before and after the Waldmeier discontinuity. The error introduced by the Waldmeier discontinuity causes R to underestimate the fitted values based on the foF2 data for 1932 - 1945, but R-BB overestimates them by almost the same factor, implying that the correction for the Waldmeier discontinuity inherent in R-BB is too large by a factor of two. Fit residuals are smallest and most uniform for R-C, and the ionospheric data support the optimum discontinuity multiplicative correction factor derived from the independent Royal Greenwich Observatory (RGO) sunspot group data for the same interval.
- 出版日期2016-11
