Abstract
The Pacific–North American (PNA) pattern is closely related to North American climate. In this study, we demonstrate that the PNA associated anomalies of North American surface temperatures and temperature extremes are modified by the extratropical Asian–Bering–North American (ABNA) teleconnection. The temperature and temperature extreme anomalies in association with the combination of the PNA and ABNA patterns are most prominent over the Canadian Prairies, and can be approximated by a linear superposition of the circulation and temperature responses to the two patterns. The various temperature responses result from the corresponding atmospheric circulation anomalies, which are associated with sea surface temperature and precipitation anomalies in the tropical eastern-central Pacific and snow cover anomalies in the Siberian region. In particular, pronounced circulation anomalies are apparent over the Great Lakes/Hudson Bay, and around the Aleutian Islands with opposite sign for the in-phase PNA and ABNA combination. This induces anomalous temperature advection and precipitation, as well as the heating associated variations of vertical motion and clouds, leading to prominent surface temperature anomalies over the Canadian Prairies directly through the variation of the surface energy budget. For the out-of-phase PNA and ABNA combination, the anomalous circulation center tends to be situated along the west coast of North America. This induces weak circulation anomalies over north-central North America and brings weak thermal advection and precipitation anomalies there, leading to insignificant temperature anomalies over the Canadian Prairies. Both the ABNA and PNA can be skillfully predicted on the seasonal time scale, as well as their pattern related North American temperature anomalies. Hence it is important to consider both tropical and extratropical sources of predictability in improving North American climate prediction skill on seasonal to interannual time scales.
Highlights
The Pacific–North American (PNA, Wallace and Gutzler 1981) pattern is one of the most well-recognized and prominent atmospheric teleconnections in the wintertime extratropical Northern Hemisphere
We examine the anomalies of North American surface temperature and temperature extremes in association with the combination of the PNA and Asian–Bering–North American (ABNA) patterns in Sect
To aid in understanding the generation and maintenance of North American surface temperature anomalies, we examine the anomalies of atmospheric circulation and thermal advection, SST, precipitation, snow water equivalent (SWE), and surface energy budget for various PNA and ABNA combinations
Summary
The Pacific–North American (PNA, Wallace and Gutzler 1981) pattern is one of the most well-recognized and prominent atmospheric teleconnections in the wintertime extratropical Northern Hemisphere. The extratropical Asian–Bering–North American (ABNA) teleconnection was constructed to directly relate the extratropical circulation anomalies to the wintertime surface temperature variability over North America by excluding the PNA pattern contribution (Yu et al 2016). It bears some resemblance to the zonal Wave pattern (Teng and Branstator 2012), especially the circulation anomalies over the North Pacific and North America, but with a zonal wavenumber 2 like structure confined to the northern mid-high latitudes (cf Fig. 11 in “Appendix A” with Fig. 1 in Teng and Branstator 2012) These findings highlight the importance of the extratropical atmospheric teleconnection and have strong implications for improving climate prediction over North America on seasonal to interannual time scales.
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