Influence of ENSO on the seasonal and extreme characteristics of ridges over Pacific-Western North American region

Atmospheric ridges are a key part of the midlatitude circulation and drive surface weather and climate. We employ a feature-tracking algorithm to identify ridge objects across Pacific-Western North America and examine their characteristics and large-scale drivers relevant for seasonal predictability. Utilizing ERA5 reanalysis, we evaluate seasonal variations in their location, frequency, extent, and intensity and explore their variations associated with ENSO variations. Focusing on extreme ridges identified based on their extent and intensity, we find that their location and characteristics depend on the ENSO phases. Large and Intense ridges tend to center over the Gulf of Alaska in most seasons. La Niña is associated with a higher frequency, extent and intensity of Intense ridges during winter and more widespread Large ridges in spring and fall seasons. Extreme ridges are typically associated with hemisphere-scale circulation anomalies and differences between their circulation patterns during ENSO phases are largely due to changes in the mean flow.