S68 Distinctive Impacts of Super–El Nino on Surface Air Temperature over North America during Its Decaying Phase

Sunday, 12 January 2020
Minghong Liu, Chinese Academy of Meteorological Sciences, Beijing, China

El Niño-South Oscillation (ENSO) has been well recognized to cause pronounced impacts on climate worldwide through atmospheric teleconnection patterns. This study analyzes the atmospheric response to the super El Niño and its distinctive impacts on surface air temperature (SAT) anomalies over North America during its decaying phase (January-April). It is clearly shown that remarkable warming appears in central-eastern North America during the super El Niño decaying, while no significant warming is detected there for moderate El Niño. These significant differences can be mainly attributed to the ENSO combination mode (C-mode) that is derived from nonlinear interactions between ENSO and Pacific warm-pool annual cycle, which is much stronger in super El Niño than that in moderate El Niño during the decaying phase. The C-mode grows into its peak during super El Niño decaying phase, with an intensive atmospheric response analogous to the Pacific-North American (PNA) pattern that causes significantly impacts in the central-eastern North America, compared to the traditional ENSO signal (commonly measured by Niño3.4 index) which is only responsible for partial anomalies in small regions of the western North America. Therefore, we propose that during super El Niño events, the observed SAT anomalies over North America can be largely captured by considering both ENSO and its associated C-mode. The linkage between the SAT anomalies over North America and the C-mode can be reasonably reproduced in model simulations. We highlight that an extended view with the C-mode participating in, could help deepen the understanding of the complex but far-reaching super El Niño’s impacts.
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