Open Access

Figure 1


Download original image

The semi-annual variation in the aaH index, available since 1868. (a) Annual means of the international sunspot number, R; (b) mean values of aaH in 30 equal-sized bins of time-of-year F as a function of F and year; (c) the mean aaH values normalized by dividing by the annual mean, 〈aaHyr; (d) a comparison of the means of aaH in quarter-year intervals around the March and September equinoxes, 〈aaHme and 〈aaHse respectively, where req = {〈aaHme − 〈aaHse}/{〈aaHme + 〈aaHse} and (e) the occurrence frequency of 3-hourly aaH values exceeding its 95 percentile, q(0.95) = 56 nT, f[aaH > q(0.95)].

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.