Pacific-North American teleconnection and North Pacific Oscillation: historical simulation and future projection in CMIP5 models

Climate Dynamics, Sep 2017

Based on reanalysis datasets and as many as 35 CMIP5 models, this study evaluates the capability of climate models to simulate the spatiotemporal features of Pacific-North American teleconnection (PNA) and North Pacific Oscillation (NPO) in the twentieth century wintertime, and further investigates their responses to greenhouse warming in the twenty-first century. Analysis reveals that while the majority (80%) of models reasonably simulate either the geographical distribution or the amplitude of PNA/NPO pattern, only half of models can well capture both features in space. As for the temporal features, variabilities of PNA and NPO in most models are biased toward higher amplitude. Additionally, most models simulate the interannual variabilities of PNA and NPO, qualitatively consistent with the observation, whereas models generally lack the capability to reproduce the decadal (20–25 years) variability of PNA. As the climate warms under the strongest future warming scenario, the PNA intensity is found to be strengthened, whereas there is no consensus on the direction of change in the NPO intensity among models. The intensification of positive PNA is primarily manifested in the large deepening of the North Pacific trough, which is robust as it is 2.3 times the unforced internal variability. By focusing on the tropical Pacific Ocean, we find that the multidecadal evolution of the North Pacific trough intensity (dominating the PNA intensity evolution) is closely related to that of the analogous trough in the PNA-like teleconnection forced by sea surface temperature anomalies (SSTa) in the tropical central Pacific (CP) rather than the tropical eastern Pacific (EP). Such association is also found to act under greenhouse warming: that is, the strengthening of the PNA-like teleconnection induced by the CP SSTa rather than the EP SSTa is a driving force for the intensification of PNA. This is in part owing to the robust enhancement of the tropical precipitation response to the CP SST variation. Indeed, further inspection suggests that models with stronger intensification of the CP SST variability and its related tropical precipitation response tend to have larger deepening magnitude of the North Pacific trough associated with the PNA variability.

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Pacific-North American teleconnection and North Pacific Oscillation: historical simulation and future projection in CMIP5 models

Clim Dyn Pacific-North American teleconnection and North Pacific Oscillation: historical simulation and future projection in CMIP5 models Zheng Chen 0 1 Bolan Gan 0 1 Lixin Wu 0 1 Fan Jia 0 1 0 Physical Oceanography Laboratory, Ocean University of China and Qingdao National Laboratory for Marine Science and Technology , 5 Yushan Road, Qingdao 266003 , People's Republic of China 1 Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences , Qingdao , People's Republic of China Based on reanalysis datasets and as many as 35 CMIP5 models, this study evaluates the capability of climate models to simulate the spatiotemporal features of PacificNorth American teleconnection (PNA) and North Pacific Oscillation (NPO) in the twentieth century wintertime, and further investigates their responses to greenhouse warming in the twenty-first century. Analysis reveals that while the majority (80%) of models reasonably simulate either the geographical distribution or the amplitude of PNA/NPO pattern, only half of models can well capture both features in space. As for the temporal features, variabilities of PNA and NPO in most models are biased toward higher amplitude. Additionally, most models simulate the interannual variabilities of PNA and NPO, qualitatively consistent with the observation, whereas models generally lack the capability to reproduce the decadal (20-25 years) variability of PNA. As the climate warms under the strongest future warming scenario, the PNA intensity is found to be strengthened, whereas there is no consensus on the direction of change in the NPO intensity among models. The intensification of positive PNA is primarily manifested in the large deepening of the North Pacific trough, which is robust as it is 2.3 times the unforced internal variability. By focusing on the tropical Pacific Ocean, we find that the multidecadal evolution of the North Pacific trough intensity (dominating the PNA intensity evolution) is closely related to that of the analogous trough in the PNA-like teleconnection forced by sea surface temperature anomalies (SSTa) in the tropical central Pacific (CP) rather than the tropical eastern Pacific (EP). Such association is also found to act under greenhouse warming: that is, the strengthening of the PNA-like teleconnection induced by the CP SSTa rather than the EP SSTa is a driving force for the intensification of PNA. This is in part owing to the robust enhancement of the tropical precipitation response to the CP SST variation. Indeed, further inspection suggests that models with stronger intensification of the CP SST variability and its related tropical precipitation response tend to have larger deepening magnitude of the North Pacific trough associated with the PNA variability. Global warming; Pacific-North American teleconnection; North Pacific Oscillation; Tropical Pacific Ocean; CMIP5 climate models - 1 Introduction As two important members of the teleconnection family in the Northern Hemisphere, the Pacific-North American teleconnection (PNA) and North Pacific Oscillation (NPO), are prominent modes of planetary-scale atmospheric variability over the North Pacific basin, with additional centers of action across the North American landmass for the PNA. The PNA is identified as geopotential height (GPH) fluctuations, whose positive phase is featured by four centers, such that two centers with above-normal heights are located near Hawaii (20°N, 160°W) and over Alberta, Canada (55°N, 115°W), and the other two with below-normal heights are centered over the North Pacific Ocean (45°N, 165°W) and over the Gulf Coast region of the United States (30°N, 85°W) (Wallace and Gutzler 1981) . The NPO is characterized as a meridional dipole of the sea level pressure (SLP), with the positive phase featured by a zonally elongated band of above-normal SLP in the subtropics and a center of below-normal SLP over Alaska. Linkin and Nigam (2008) further pointed out that the NPO is the SLP signature of the West Pacific (WP) teleconnection pattern in the upperlevel geopotential height, which is the second leading mode behind the PNA mode (Wallace and Gutzler 1981) . Both the PNA and NPO, prominent in boreal winter, have close relationships with fluctuations in the position and strength of the Asian-Pacific jet stream and the North Pacific storm tracks, and have powerful influences on the North American hydroclimate. The positive PNA is associated with the enhancement and eastward extension of the jet stream, while the northward displacement and elongation of the jet exit region is linked to the positive NPO, and vice versa (e.g., Linkin and Nigam 2008; Wettstein and Wallace 2010) . Under the framework of eddy-mean flow interaction, the PNA and NPO also modulate variations of storm tracks in association with the anomalous jet, such as a southward shift and downstream intensification of storm tracks corresponding to the positive phases of the PNA an (...truncated)


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Zheng Chen, Bolan Gan, Lixin Wu, Fan Jia. Pacific-North American teleconnection and North Pacific Oscillation: historical simulation and future projection in CMIP5 models, Climate Dynamics, 2017, pp. 4379-4403, Volume 50, Issue 11-12, DOI: 10.1007/s00382-017-3881-9