Geomagnetic activity: long- and short-term variability, sources
V. Dobrica1, K. Georgieva2, B. Kirov2, C. Demetrescu1
1
Institute of Geodynamics, Romanian Academy, Bucharest, Romania, venera@geodin.ro
Space and Solar-Terrestrial Research Institute, Bulgarian Academy of Sciences, Sofia,
Bulgaria
2
The interaction of the solar wind and heliospheric magnetic field with the Earth’s magnetic
field leads to developing, in the magnetosphere and ionosphere, of several current systems.
The overall effect of these current systems is quantified at the Earth’s surface by means of
geomagnetic activity via geomagnetic indices: Dst, SYM-H, ASY-H (magnetospheric ring
current), AE (auroral electrojet), PC (electric field and convection in the polar ionosphere), aa
(mid-latitude geomagnetic activity) and Ap (planetary geomagnetic activity). In this study we
discuss the correlation between pairs of indices at various time scales, from hours to
interdecadal, showing the effect of long-term solar activity on the magnetosphere variability,
as well as the two solar sources of the geomagnetic activity (sunspot- or non-sunspot-related)
in relation to solar magnetic field. The latter is discussed in the perspective offered by the aa
geomagnetic index, a carrier of information on both coronal mass ejections and high speed
streams in the solar wind.