Trends in the solar quiet geomagnetic field variation linked to the Earth's magnetic field secular variation and increasing concentrations of greenhouse gases

ANA G. ELIAS; MARTA ZOSSI DE ARTIGAS; BLAS F. DE HARO BARBAS

JOURNAL OF GEOPHYSICAL RESEARCH

AMER GEOPHYSICAL UNION

Año: 2010 vol. 115 p. 8316 - 8323

0148-0227

Long-term trends in solar quiet geomagnetic field variation are studied in connection to the Earth magnetic field secular variations and increasing greenhouse gas concentrations. Sq is mainly caused by ionospheric current systems that flow in the E region and depends, among other variables, on the ionospheric conductivities. These conductivities in turn depend on the Earth main magnetic field (B) and the electron concentration in the E region, for which is a measure of its peak value. Since secular variation, induced long term changes in Sq might be expected. Another possible mechanism that would be able to induce trends is the increasing concentrations of greenhouse gases that produce a cooling effect in the upper atmosphere and, according to model predictions and experimental results, an increasing trend in E. To detect if both mechanisms mentioned are able to induce trends in Sq the variation of the horizontal intensity of three magnetic observatories (Apia, Fredericksburg, and Hermanus), for which B is decreasing, is analyzed for the period 1960-2001. We find significant increasing trends (6.6%, 5.4%, and 9.9%, respectively) which may be partially accounted for by secular variations in the respective sites. The trend expected from E increase is low (0.5%), although positive, as is the observed trend.