Possible influence of solar/geomagnetic activity on climate variability has been a subject of many recent studies, due to a substantial increase of solar/geomagnetic activity during the last century. There is no generally accepted mechanism for tropospheric responses to the variability in solar/geomagnetic activity up to now. Long-term records of the near surface air temperature from several midlatitude European locations, the North Atlantic Oscillation (NAO) index, as well as the geomagnetic activity aa-index and the sunspot numbers have been analyzed to detect possible common oscillatory modes. The statistically significant oscillatory modes with a period of approximately 8 years have been detected in the geomagnetic activity index as well as in the NAO index and surface air temperature records. The existence of the common oscillatory mode gives us a solid basis for further research of relations between the geomagnetic activity and climate variability (Paluš and Novotná, 2007).

The research into solar effects on tropospheric circulation has been extended to the effects of the 11-year solar cycle on the frequency, duration, and position of blocking highs; the frequency of synoptic types; and the Arctic Oscillation. Statistically significant differences between solar maxima and minima appear for all the circulation characteristics. The general effect is that under high solar activity, the circulation tends to zonalize. High solar activity is also accompanied by a larger geographical extent of blocks and more positive and more variable Arctic Oscillation. One of the most striking solar effects is the different frequency of westerly and easterly Hess-Brezowsky synoptic types: whereas under low solar activity, the westerly types are about twice as frequent as the easterly types, under high solar activity the westerly types occur four times more frequently than the easterly ones (Huth et al., 2007, 2008c; Barriopedro et al., 2008).

In research on modes of atmospheric circulation variability, we contributed to a hot scientific debate on whether Arctic Oscillation (AO) or North Atlantic Oscillation (NAO) should be considered as the leading mode of the low-frequency variability in the Northern Hemisphere, that is, whether the hemispheric or sectorial view of the variability should be preferred. We used mainly statistical arguments and demonstrated that the AO is likely a statistical artifact and that its Pacific centre is a result of a high local variability rather than of its relationships with the Arctic and Atlantic centres; therefore, we suggest that it is the NAO that should be viewed as the primary mode of variability (Huth, 2007). We also examined, in terms of correlation coefficients, the effects the variability modes have on surface climate elements (including temperature, cloudiness, sunshine duration, wind components, and precipitation amount and probability) in the Czech Republic and on temperature and precipitation over Europe. We took into account the major modes in the Euro-Atlantic sector, viz., the NAO, the East Atlantic mode, and two Eurasian modes (Pokorná et al., 2007). The correlations between the circulation variability modes and surface climate elements vary considerably in time; a major contributor to the variations are geographical shifts in the action centres of the modes (Beranová and Huth, 2007, 2008; Pokorná et al., 2007).

Relationships between persistent circulation patterns and surface air temperature anomalies were studied over the 20th century using the Hess-Brezowsky catalogue of circulation types and long-term temperature series over the European continent. Types significantly conducive to heat and cold waves were identified, and temperature anomalies were linked to their persistence. More persistent circulation tends to enhance the severity of both warm and cold temperature extremes; the effects depend on the circulation type and the roles of radiative/advective mechanisms of local temperature changes (Kyselý, 2007, 2008b).