Tests of sunspot number sequences: 1. Using ionosonde data

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/Zürich/International sunspot number [R], the new “backbone” group sunspot number [RBB] and the proposed “corrected sunspot number” [RC]. 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, RBB, and RC largely differ in their allowance for the “Waldmeier discontinuity” around 1945 (the correction factor for which for R, RBB and RC 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 RBB. We here use foF2 for those UTs for which R, RBB, and RC 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 RBB overestimates them by almost the same factor, implying that the correction for the Waldmeier discontinuity inherent in RBB is too large by a factor of two. Fit residuals are smallest and most uniform for RC 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

The importance of the Antarctic in atmospheric sciences

A prime objective of atmospheric science research in Antarctica is to use the special conditions found there to throw new light on global problems and, in particular, to test theories of the dynamics of the environment and its reactions to solar phenomena. This involves much international collaboration in planning, data collection and analysis, which is briefly described. The British Antarctic Survey theatre of operations is geographically and magnetically unique and therefore offers exceptionally favourable conditions for such tests. The development of new instruments, in particular those carried by satellite, has made research possible in uninhabited regions and enabled problems to be studied which were previously impracticable. The objects of this paper are to draw attention to the needs and possibilities, and to show some of the ways in which the specific investigations discussed by other contributors interact

Combination of ionosonde and riometer data for absorption measurements

A method is described for combining ionosonde and riometer data which overcomes limitations in both techniques for the measurement of normal absorption in the lower ionosphere. The usefulness of these techniques is thereby considerably increased

Solar proton and electron precipitation effects detected by ionosondes

Anomalous polar absorption events detected by means of ionosondes at four stations in the northern hemisphere and four in the southern hemisphere have been compared with energetic particle events observed by means of satellites during a five-year period. One-quarter of the solar proton events detected by satellites resulted in significant changes of f-min. A table giving details of all the anomalous ionospheric events and some of the associated particle fluxes is given for the years 1964–1969