Position, Magnitude, and Size of Warm-Pool El Niño : Variability, Seasonal Predictability, and Climate Impacts

This study surveys the variability and predictability of the position, magnitude, and size of warm-pool El Niño (WP El Niño), as well as its impacts on the climate. A new detection method for WP El Niño that is flexible regarding its position, magnitude, and size is developed. Thirteen WP El Niño events are found from 1950 to 2018 using this detector. These events have a mean (standard deviation) center position of 31.7 (12.4)° longitude, a mean peak sea surface temperature anomaly (SSTA) of 1.87 (0.62) K, and a zonal size parameter of 19.99 (5.13)° longitude. Also, stronger WP El Niño events tend to be larger and take place farther east. Based on these distributions, a set of model experiments is conducted to evaluate climate sensitivity to these three features. The wintertime North American temperature dipole due to WP El Niño is chosen as an example. Its bearing is linearly controlled by the position of the SSTA field of WP El Niño, and this control is stronger when the SSTA field is stronger or smaller. Predictability of position, magnitude, and size of WP El Niño on seasonal scale by the North American Multi-Model Ensemble is examined. With a 2-month lead-time, the position and magnitude of WP El Niño are predicted accurately, but size tends to be large-biased. Increasing the lead-time generally leads to more eastward bias, cold bias, and large bias. Precision of the predictions is also reduced with lead-time.