Impacts of two types of La Niña on the NAO during boreal winter

Abstract

The present work identifies two types of La Niña based on the spatial distribution of sea surface temperature (SST) anomaly. In contrast to the eastern Pacific (EP) La Niña event, a new type of La Niña (central Pacific, or CP La Niña) is featured by the SST cooling center over the CP. These two types of La Niña exhibit a fundamental difference in SST anomaly evolution: the EP La Niña shows a westward propagation feature while the CP La Niña exhibits a standing feature over the CP. The two types of La Niña can give rise to a significantly different teleconnection around the globe. As a response to the EP La Niña, the North Atlantic (NA)-Western European (WE) region experiences the atmospheric anomaly resembling a negative North Atlantic Oscillation (NAO) pattern accompanied by a weakening Atlantic jet. It leads to a cooler and drier than normal winter over Western Europe. However, the CP La Niña has a roughly opposing impact on the NA-WE climate. A positive NAO-like climate anomaly is observed with a strengthening Atlantic jet, and there appears a warmer and wetter than normal winter over Western Europe. Modeling experiments indicate that the above contrasting atmospheric anomalies are mainly attributed to the different SST cooling patterns for the two types of La Niña. Mixing up their signals would lead to difficulty in seasonal prediction of regional climate. Since the La Niña-related SST anomaly is clearly observed during the developing autumn, the associated winter climate anomalies over Western Europe could be predicted a season in advance.

Asymmetry of the winter extra-tropical teleconnections in the Northern Hemisphere associated with two types of ENSO

“…It is reported that based on the current indices it is not easy to classify the two types of ENSO, especially for the two types of La Niña (Ren and Jin 2011;Zhang et al 2014b). Thus, none of the two documents are consensus for the selection of the EP and CP ENSO.…”

The Stratospheric Pathway of La Niña

“…Several indices have been used in the literature, considering different oceanic regions, such as Nino-3 (N3) (5°N-5°S, 150°-90°W) (Hoerlinget al 1997;Manzini et al 2006) or Nino-4 (N4) (5°N-5°S, 160°E-150°W) (Kug and Ham 2011;Zhang et al 2015). However, most recent studies used the Nino-3.4 (N3.4) (5°N-5°S, 170°-120°W) index from the National Centers for Environmental Prediction/Climate Prediction Center (NCEP/CPC) (e.g., Free and Seidel 2009;Butler and Polvani 2011;Garfinkel et al 2012;Butler et al 2014;Barriopedro and Calvo 2014;Domeisen et al 2015).…”

Seasonal predictability of winter ENSO types in operational dynamical model predictions

“…Note that the classification for La Niña events is still controversial. Here we directly refer to the previous study (Zhang et al 2015). The winters for the different types of winter-mean ENSO indices are listed in Table 2.…”

“…However, they were also divided into the two types in some studies (Ashok and Yamagata 2009;Yuan and Yan 2013), particularly if the decadal background is eliminated since 1980 . Indeed, the value of distinguishing the two types for either El Niño or La Niña events is clearest from their distinct global and regional climate impacts rather than their different SST patterns (Zhang et al 2015). From this point of view, both types of El Niño and La Niña events will be focused on in this study.…”