Impacts of large-scale oscillations on climate variability over North America

The ocean is the main driver of internal climate variability. However, the relatively short length of the historical record limits our ability to study the impact of large-scale oscillations on the regional climate. This work uses the output from the Canadian Earth System Model large ensemble (CanESM2-LE) to study the impact of three large-scale oscillations on temperature and precipitation anomalies over North America. The 50-member ensemble provides data series covering 2500 years to study the superpositions between ENSO, AMO, and PDO over the 1961–2010 period. The main characteristics of all three oscillations are well reproduced by CanESM2-LE. The impact of each oscillation is considered independently (with the others in their neutral phases), as well as combined with the other two (e.g., all three in non-neutral phases). The results outline a dominant role of ENSO in annual precipitation and of AMO in temperature over most of North America. PDO has a minimal impact on precipitation and temperature. The dominant roles of ENSO on precipitation and AMO on temperature are enhanced by superpositions between these patterns. These combined impacts are consistent with their independent ones. Even though this study is conducted in a model world, the superpositions are mostly consistent with our understanding derived from observations. The results therefore extend our understanding of the relationship between large-scale oscillations and climate variability over North America and highlight the importance of considering the superpositions between oscillations to better understand internal hydroclimatic variability.