Long‐term trends in solar quiet geomagnetic field variation (Sq) are studied in connection to the Earth's 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's main magnetic field (B) and the electron concentration in the E region, for which foE is a measure of its peak value. Since B shows secular variation, induced long‐term changes in Sq might be expected. Another possible mechanism that would be able to induce Sq 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 foE. To detect if both mechanisms mentioned are able to induce trends in Sq, the Sq variation of the horizontal intensity (H) 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 B secular variations in the respective sites. The Sq trend expected from the theoretically predicted foE increase is low (∼0.5%), although positive, as is the observed trend.

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[1] The QBO of the zonal wind in the equatorial stratosphere between 15 and 70 hPa is analyzed in connection to the solar UV flux. F10.7 is used as a UV proxy after filtering out its long-term variations. A running correlation between F10.7 filtered values and the equatorial zonal wind was estimated. A clear oscillation of around 11 years can be noticed in the running correlation coefficients, with maximum negative and positive values around maximum and minimum solar activity respectively, between 50 and 15 hPa. In coincidence with other authors, during maximum solar activity, higher (lower) UV levels occur during the QBO easterly (westerly) phase. During minimum solar activity this relationship is reversed. A link between these results and the association between the equatorial QBO and the polar winter is suggested together with a mechanism of association between the UV QBO and the zonal equatorial wind in the stratosphere.