Trends in space weather since the nineteenth century

Abstract

In this paper we present trends and variations of in the geomagnetic activity as signatures of space weather and climate during the last 166 years. The data used are global and local magnetic activity index series. The global indices are daily aa-numbers for 1868-2010, and the local ones are derived from Helsinki (1844-1897) and Sodankylä (1914-2010) magnetic observatory recordings. Geomagnetic and solar activity was in deep minimum in early decades of the twentieth century when the global activity was on average about half of that during the last two sunspot cycles in 1986-2009 (23 and 24). However, the prolonged duration of the sunspot cycle 23 (1996-2008) and the slow progress of the solar activity during the present cycle 24, indicate that the Sun will be in less active state during the coming decade. The average magnetic activity in 2008-2009 was lowest for about 100 years. © 2012 Springer-Verlag Berlin Heidelberg.