Impacts of the EA and SCA patterns on the European twentieth century NAO–winter climate relationship

Abstract

Much of the twentieth century multidecadal variability in the relationship between North Atlantic Oscillation (NAO) and winter climate over the North Atlantic–European sector can be linked to the combined effects of the NAO and either the East Atlantic pattern (EA) or the Scandinavian pattern (SCA). Our study documents how different NAO–EA and NAO–SCA combinations influence winter climatic conditions (temperature and precipitation) as a consequence of NAO dipole migrations. Using teleconnectivity maps, we find that the zero‐correlated line of the NAO–winter‐climate relationship migrates southwards when the EA is in the opposite phase to the NAO, related to a southwestwards migration of the NAO dipole under these conditions. Similarly, a clockwise movement of the NAO–winter‐climate correlated areas occurs when the phase of the SCA is opposite to that of the NAO, reflecting a clockwise movement of the NAO dipole under these conditions. Our study provides new insights into the causes of spatial and temporal nonstationarity in the climate–NAO relationships, particularly with respect to winter precipitation. Furthermore, interannual variability in the north–south winter precipitation gradient in the UK appears to reflect the migration of the NAO dipole linked to linear combinations of the NAO and the EA. The study also has important implications for studies of the role of the NAO in modulating the wind energy resource of the UK and Ireland, as well as for the selection of locations for terrestrial proxy archive reconstruction of past states of the NAO.

Mechanisms of northern North Atlantic biomass variability

“…Foukal and Lozier [2017 provide an updated analysis 370 with respect to the relationship of physical changes in the gyre to the East Atlantic Pattern (EA) and the North Atlantic Oscillation (NAO). While the EA indicates the position of the westerly winds, NAO indicates their strength [Foukal and Lozier, 2017;Comas-Bru and McDermott, 2014]. A preliminary investigation using the winter (DJFM) EA index from NOAA CPC indicates that only in the nutrient-limited SE region are there significant correlations.…”

Historical Climate off the Atlantic Iberian Peninsula

“…However, to explain the occurrence of big storms clustered in the early MWP on the northwestern IP (off the Douro River), one has to imply a storm track position southward of the modern path of the westerly winds under NAO+ conditions, to at least 41ºN, a shift that could have been caused 15 by an increase in mid-latitude blocking anticyclones. The SCAND is related to major blocking anticyclones over Scandinavia and has a positive mode associated with above-average precipitation across southern Europe (Comas-Bru and McDermott, 2014;Jerez and Trigo, 2013). Although considered to have a larger influence on the IP in summer than in winter, (Hernández et al, 2015) attribute the interannual winter variability in the northern IP lake Sanabria to the joint action of NAO 20 and SCAND modes, while EA appears to have a weak influence in summer.…”

“…CC-BY 3.0 License. based indices for different NAO and EA indices of (Comas-Bru and McDermott, 2014), the authors propose equally negative NAO and EA during the LIA, as well as an equally positive NAO and EA during the MWP. On the contrary, NAO-and EA+ would explain the warm temperatures and E-W humidity gradient before 500 CE, while the inverse conditions between 500 -900 CE could be explained by a NAO+ but EA-.…”

“…Other prominent modes of climate, the East Atlantic (EA) and the Scandinavia (SCAND) (Comas-Bru and McDermott, 2014;Jerez and Trigo, 2013), constitute second leading modes, which interplay with 25 the NAO, and their temporal variability, must have also had a role on the climatic evolution of the north Atlantic. The EA has a strong effect on the strength and location of the NAO dipoles mainly on a multidecadal time-scale, and according to (Hernández et al, 2015), has a major control on winter and summer temperature over the Iberian Peninsula.…”

Data-model comparison of soil–water δ 18 O at a temperate site in N. Spain with implications for interpreting speleothem δ 18 O

“…An understanding of the processes causing this observed attenuation of the δ 18 O sw signal is important if speleothem time-series oxygen isotope data can be sampled and analysed at a finer temporal resolution than the timescale of homogenisation, or if the climate signal of interest has a strong seasonal expression (e.g. inter-annual variability in winter δ 18 O p associated with changes in the North Atlantic Oscillation; Baldini et al, 2008;Comas-Bru and McDermott, 2014). In this study, oxygen isotope ratios have been measured in rain and soil-waters that were sampled monthly above La Garma cave in N. Spain (Figure 1).…”