A distinct and reproducible teleconnection pattern over North America during extreme El Nino events

Abstract

El Nino-Southern Oscillation (ENSO) teleconnections are an important predictability source for extratropical seasonal climate forecasts. Previous studies suggest that the ENSO teleconnection pattern depends on the ENSO phase (El Ni�o vs. La Ni�a) and/or Sea Surface Temperature (SST) pattern (central Pacific vs. eastern Pacific El Ni�o events). Observations and ensemble simulations with the CNRM-CM6.1 atmospheric general circulation model indicate that only extreme El Ni�o events (e.g. 1982-1983, 1997-1998, 2015-2016) display a statistically significant eastward shift relative to the well-known Pacific-North American teleconnection pattern that occurs during both central and eastern Pacific moderate El Ni�o or during La Ni�a. This specific teleconnection pattern emerges when equatorial SST anomalies are both eastward-shifted and sufficiently large to exceed the deep atmospheric convection threshold over most of the eastern Pacific, resulting in a basin-wide reorganization of tropospheric heat sources. It yields> 0.5 std wet conditions over Western United States (74% likelihood) as well as> 0.5 std warm anomalies over Canada and the Northern United States (71% likelihood), with more consistency across events and ensemble members than for any other El Ni�o or La Ni�a type. These findings hold important implications for the seasonal forecasting of El Ni�o�s impacts on the North American climate.