P. Schmoldt, PhD - MTNet - DIAS

2.2. Electric currents in the magnetosphere
Fig. 2.5.: Monthly average of observed sunspot numbers since 1749 (in blue) and the more sporadic observations prior to 1749 (in
red) until 2001, exhibiting a prominent 11 year cycle and periods of altered activity, after Hoyt and Schatten [1998a,b].
Fig. 2.6.: Monthly (blue) and monthly smoothed (red) sunspot numbers since 1950 until 2010 showing a minimum of solar activity for
the time of the fieldwork campaign in 2007, from Solar Influence Data Analysis Center (SIDC), Royal Observatory of Belgium [2010]
small amplitudes, which makes the response estimation very difficult given the insufficient
baseline stability of electric sensor systems for such a long duration. Special setups
are necessary to utilise semi-annual variation signal, e.g. the experiment by Schultz et al.
[1993] in which electric recording instruments (electrodes) were placed in lakes for thermal
and chemical stability.
2.2.2. Regular variations
Regular variations terms effects that occur constantly but are variable in intensity, depending
on the present strength of the solar activity and the resulting solar wind.
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