Are the Winters 2010 and 2012 Archetypes Exhibiting Extreme Opposite Behavior of the North Atlantic Jet Stream?*

Abstract

The atmospheric circulation over the North Atlantic-European sector experienced exceptional but highly contrasting conditions in the recent 2010 and 2012 winters (November-March, with the year dated by the relevant January). Evidence is given for the remarkably different locations of the eddy-driven westerly jet over the North Atlantic. In the 2010 winter the maximum of the jet stream was systematically between 308 and 408N (south jet regime), whereas in the 2012 winter it was predominantly located around 558N (north jet regime). These jet features underline the occurrence of either weak flow (2010) or strong and persistent ridges throughout the troposphere (2012). This is confirmed by the very different occurrence of blocking systems over the North Atlantic, associated with episodes of strong cyclonic (anticyclonic) Rossby wave breaking in 2010 (2012) winter. These dynamical features underlie strong precipitation and temperature anomalies over parts of Europe, with detrimental impacts on many socioeconomic sectors. Despite the highly contrasting atmospheric states, mid-and high-latitude boundary conditions do not reveal strong differences in these two winters. The two winters were associated with opposite ENSO phases, but there is no causal evidence of a remote forcing from the Pacific sea surface temperatures. Finally, the exceptionality of the two winters is demonstrated in relation to the last 140 years. It is suggested that these winters may be seen as archetypes of North Atlantic jet variability under current climate conditions.

The Anomalous Merging of the African and North Atlantic Jet Streams during the Northern Hemisphere Winter of 2010

“…The El Niño conditions during winter 2010 prompted Santos et al (2013) to examine the role of the tropical Pacific in forcing the variability of the Atlantic jet, but contrary to our findings, they did not find a significant signal. To further verify the robustness of our results, we repeated the composite calculations using subsets of the data.…”

“…Indeed, an examination of the interannual variability in the Atlantic jet structure suggests that, during some years, a single rather than double jet forms (Woollings et al 2010b). Most striking is the winter of 2010 (hereafter, winter refers to December-March months, with the year referring to January-March), which exhibited an unusually strong and persistent negative phase of the North Atlantic Oscillation (NAO) and unusually cold and wet conditions over North America and Europe (Wang et al 2010;Seager et al 2010;Cattiaux et al 2010;Vicente-Serrano et al 2011;Santos et al 2013). As shown below, during this winter, the Atlantic and African jets merged into one zonally oriented jet with a structure and variability more characteristic of the Pacific.…”

The Melting Arctic and Midlatitude Weather Patterns: Are They Connected?*

“…During much of winter 2009/10 the polar jet was displaced southward in association with a negative NAO phase, bringing prolonged cold temperatures to northwestern Europe. In the winter of 2011/12, the jet was displaced northward as a result of persistent ridging in the Atlantic, consistent with a positive NAO phase (Santos et al 2013). Winter 2013/14 followed neither of these patterns, and was instead dominated by a centrally located jet that created exceptionally wet, stormy, and mild weather in the United Kingdom (Slingo et al 2014;Matthews et al 2014).…”

Drought impact on carbon and water cycling in a Mediterranean <i>Quercus suber</i> L. woodland during the extreme drought event in 2012

“…2a and b). In particular, the winter of 2011/2012 was very dry over south-western Iberia, with only about 20 % of the long-term precipitation (Santos et al, 2013;Trigo et al, 2013). 2012 was the second driest year since 1950.…”

“…Particularly, 2012 showed a severe additional winter/spring drought characteristic for precipitation pattern changes in the recent past on the Iberian Peninsula (second driest year since 1950, Costa et al, 2012;Santos et al, 2013;Trigo et al, 2013). This study focuses on (1) quantifying the effects of drought on the local ecosystem water balance, overstorey and understorey GPP, as well as differences in net ecosystem carbon exchange NEE between both years, and (2) identifying physiological responses in the drought year 2012 of the Q. suber trees using a combined photosynthesis-stomatal conductance model and testing the model performance with different process descriptions.…”