Combined Impacts of PDO and Two Types of La Niña on Climate Anomalies in Europe

Abstract

Combined impacts of the Pacific decadal oscillation (PDO) and two types of La Niña on climate anomalies in Europe are studied. Particularly, the conjunction of the negative PDO phase and two different types of La Niña events favors strong and significant North Atlantic Oscillation (NAO) pattern anomalies with opposite polarity. For the central Pacific (CP) La Niña, a clear positive NAO signal can be detected, which is accompanied by positive surface air temperature (SAT) anomaly and a dipolar structure of precipitation anomalies in Europe. In addition, a typical negative Pacific–North America (PNA) teleconnection pattern forms, including a high pressure anomaly over the southeastern United States, which may contribute to the development and maintenance of the NAO anomaly by strengthening the baroclinicity and the local eddy–mean flow interaction. However, for the eastern Pacific (EP) La Niña, a zonal wave train in the high latitudes can be observed, which is quite different from the typical PNA structure. Here, an anomalous anticyclone over southern Greenland supports a negative NAO pattern through the local eddy–mean flow interaction and the associated vorticity advection. Hence, reversed SAT and precipitation anomalies occur over Europe. Further analyses indicate that the wave trains emanating from the North Pacific and the synoptic eddy–mean flow interaction play essential roles in forming the anomalous NAO phases. The different wave trains for the CP and EP La Niña events may be attributed to the differences in the location and intensity of anomalous convection induced by different types of SST anomaly as well as by the corresponding background westerly wind anomalies in the upper troposphere.

Teleconnection Processes Linking the Intensity of the Atlantic Multidecadal Variability to the Climate Impacts over Europe in Boreal Winter

“…In terms of atmospheric circulation, slackened Aleutian Low as part of a larger scale Rossby wave pattern cascading into the North Atlantic, is also detectable in the model (not shown), but the amplitude of the Pacific-Atlantic teleconnection is lower in CNRM-CM5 compared to other models taken from the DCPP-C database (Ruprich-Robert et al 2019). We thus interpret the dynamical response over Europe as primarily driven by the local Atlantic influence with some modulation from the Pacificinitiated wave train in line with Ding et al (2017)'s findings from observations. The role of the PDV, which is likely function of AMV-forcing amplitude, however remains to be better quantified but a deeper analysis goes beyond the scope of the present paper.…”

Influence of multidecadal variability on high and low flows: the case of the Seine basin

“…The potential mechanisms linking the SST anomalies in the North Pacific and multidecadal hydroclimate variations over France are not clear. Ding et al (2017) suggest that the Pacific Decadal Variability (PDV) (Mantua and Hare, 2002) combined with La Niña events could result in precipitation and temperature anomalies over Europe by favoring NAO-like circulation patterns. The phase of the NAO and therefore the sign of precipitation and temperature anomalies is dependent on the type of La Niña.…”

Climate variability in Iran in response to the diversity of the El Niño‐Southern Oscillation

“…By averaging the data for four EP El Niño, six CP El Niño and nine La Niña events, a composite view of ENSO has been produced. It should be noted that some authors have mentioned that there are also two types of La Niña (e.g., Kao and Yu, ; Yu et al, ; Ding et al, ), but as La Niña events only show subtler inter‐event differences in the spatial patterns of SST anomalies (Capotondi et al, ), the present study only focuses on La Niña in general and the two types of El Niño.…”