On the nature of the steep changes in solar and geomagnetic activity after 1705, 1923 and 1993

Details On the nature of the steep changes in solar and geomagnetic activity after 1705, 1923 and 1993 On the nature of the steep changes in solar and geomagnetic activity after 1705, 1923 and 1993

Sep 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003esasp.535...91d&link_type=abstract

In: Solar variability as an input to the Earth's environment. International Solar Cycle Studies (ISCS) Symposium, 23 - 28 June 2

Statistics

Methodology

3

Sun: Activity, Geomagnetic Field: Activity

Scientific paper

It was shown that the 11-year cycle amplitude modulation has suffered an ascending chaotic transition after 1923, leading the solar mean magnetic field almost to duplicate in less than 30 years, and that a descending transition started at year 1993. To investigate the nature of these steep changes we perform a multi-resolution wavelet analysis of the relationship between long term evolution in Wolf sunspot number, geomagnetic index aa time series and 158-day periodicity in sunspots (1844-2002). The same methodology is applied to the study of the sudden commencement index (SSC) (1968-1993), defined for each storm as the product of its amplitude and rise time. We find that the chaotic ascending transition is synchronic with the strengthening of the 158-day periodicity, while the SSC index is inversely related to the 158 days periodicity and had reached during sunspot cycle 22 its largest value since 1868. In the light of dynamo theory we conclude that new magnetic flux has been injected to the dynamo layer from the convective region during the ascending transition wile during cycle 22 strong toroidal fields were ejected by the solar dynamo system leading to intense sudden commencement geomagnetic storms.

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