4th IAGA/ICMA/CAWSES Workshop on Long-Term Changes and Trends in the Atmosphere, Sodankylä, Finland, 4-8 September 2006

Long-term changes and trends (over the last 100 years) in geomagnetic and solar activity

M. A. Clilverd¹, Th.Ulich², H. Rishbeth³, E. Clarke⁴

¹British Antarctic Survey, Cambridge, England, U.K.,
²Sodankylä Geophysical Observatory, Sodankylä, Finland,
³University of Southampton, Southampton, England, U.K.,
⁴British Geological Survey, Edinburgh, Scotland, U.K.

Abstract

The clearest periodicity exhibited by solar activity is the quasi 11-year Schwabe cycle. However, over longer timescales, many other periods influence the overall levels of solar activity. Over much of the last 100 years solar activity has shown an increasing trend following a quiet period at the beginning of the 1900's. Will these high levels of solar activity continue or should we expect a period of low solar activity in the future?

Solar activity, often defined by sunspot number, disturbs near-Earth plasmas, and as a result affects the Earth environment in many varied ways. Periodicities in solar activity can influence the frequency and intensity of space weather events. Increased solar activity through EUV irradiance reduces the lifetime of low-Earth-orbiting satellites by increasing the neutral density of the atmosphere (~150-1000km). Geomagnetic storms closely follow solar activity changes and also produce short-term variations in neutral density, composition, and enhance ionospheric current systems. Individual geomagnetic activity events tend to produce greater relative depression of F2-layer electron density in a solar cycle with lower F10.7 than in ones of higher F10.7. Clearly, long-term variations in solar activity are communicated to the Earth's atmosphere in many complex ways.