Enhanced signature of solar variability in Eurasian winter climate

Abstract

[1] We demonstrate that open solar flux (F s , derivable from geomagnetic data) exhibits stronger correlations with atmospheric circulation variations than conventionallyused measures of solar activity. The circulation anomalies are particularly enhanced over the North Atlantic/Eurasian sector, where there are large changes in the occurrence of blocking and the winter mean surface temperature differs by several degrees between high-and low-solar terciles. The relationship is stronger and simpler for F s , being more linear between high-and low-solar winters. While the circulation anomalies strongly resemble the North Atlantic Oscillation they also extend deeper into Eurasia, especially in high-solar conditions. This distinct signature may be useful for the detection and attribution of observed changes and also the identification of dynamical mechanisms.

Solar Influence on Global and Regional Climates

“…It should be noted that they used geomagnetic activity indices as indicators of the probability of SEP fluence, and these correlate highly with the open solar flux F S . Thus, it is likely they are observing the same phenomenon as reported by Lockwood et al (2010a), Woollings et al (2010b) and Bochníček and Hejda (2005) but are using an interpretation based on the model predictions of SEP effects by Rozanov et al (2005Rozanov et al ( , 2012. Similarly, the effect reported by Lu et al (2008) which they attributed to the solar wind could well be via a correlation with open solar flux.…”

“…For example, the effects of the changed position and frequency of blocking events may be seen as a manifestation of modes of lowfrequency circulation variability which have been found to respond to solar activity giving increased/decreased frequencies of easterly/westerly circulation patterns over Europe under low-solar activity conditions (Huth et al 2006. Figure 7 (from Woollings et al 2010b) studies changes in the occurrence of DJF blocking events, using the means of the blocking index of Berrisford et al (2007) from the same data set as used in Fig. 6.…”

“…Contours are drawn every 2%, with positive/negative contours in red/blue, respectively, with the zero contour omitted. The grey area shows where the anomalies are significant at the 99% level, defined using a Monte-Carlo technique (from Woollings et al 2010b) Surv Geophys (2012) 33:503-534 519 Winter CET values are known to be strongly modulated by the NAO (Karoly and Stott 2006), and modelling has shown that stratospheric trends over recent decades, along with downward links to surface, are indeed strong enough to explain much of the prominent trend in the NAO and hence regional winter climate in Europe between the 1960s and the 1990s (Scaife et al 2005). Furthermore, tropospheric blocking episodes are known to influence the stratosphere, and there have been strong suggestions that the coupling works both ways, such that they are also influenced by the stratosphere ).…”

“…Blocking episodes comprise extensive and quasi-stationary anticyclones which can persist for several weeks, leading to extended cold periods in winter as the mild maritime westerly winds are replaced by continental north-easterlies and the land surface cools under cloudless skies. These changes are associated with a meander in the jet stream in the upper troposphere and lower stratosphere, such that its usual eastward (westerly) (Uppala et al 2005) extended to cover 44 complete winters (1957/1958 to 2000/2001) using operational data (from Woollings et al 2010b). A bootstrap test was employed, resampling the sets of winters in order to estimate the sampling uncertainty, to test whether the solar pattern in a was different from that associated with the NAO in b: this found that the two patterns are significantly different at the 93% level flow becomes south-westward around the longitude of the event centre ).…”

Solar forcing for CMIP6 (v3.2)

“…More recently, it has become better established that there is a solar response in the Arctic Oscillation (AO) and NAO from the top-down mechanism (Shindell et al, 2001;Kodera, 2002;Matthes et al, 2006;Woollings et al, 2010;Lockwood et al, 2010;Ineson et al, 2011;Langematz et al, 2013;Maycock et al, 2015;Thieblemont et al, 2015). Earlier models often employed a lower vertical domain, missing key physical processes by which solar signals in the stratosphere couple to surface winter climate.…”