Asymmetric impacts of Arctic sea ice anomalies on El Niño-Southern Oscillation

Abstract

The impact of Arctic sea ice concentration (SIC) anomalies on the global climate system has received considerable attention in recent decades. Observations and model simulations indicate that winter Arctic SIC anomalies in the Greenland-Barents Seas significantly influence on the El Niño-Southern Oscillation (ENSO). However, whether this influence is symmetric remains unclear. Here, we demonstrate that the influence of SIC anomalies on the subsequent ENSO is asymmetric. An increase in SIC significantly affects the development of El Niño, whereas a decrease in SIC has only a weak influence on La Niña. Specifically, a winter SIC increase in the Greenland-Barents Seas induces deep Arctic cooling, which triggers an atmospheric wave train propagating to the subtropical North Pacific. The associated subtropical cyclonic anomaly leads to North Pacific Meridional Mode-like sea surface temperature (SST) warming in spring, which extends to the tropical Pacific via the wind-evaporation-SST feedback in the following summer and subsequently enhances El Niño development by tropical air-sea interaction processes. In contrast, a winter SIC decrease is accompanied by shallow Arctic warming, which is insufficient to generate an atmospheric wave train to modify the subtropical North Pacific oceanic and atmospheric states, and thus has a weak influence on the La Niña development. Further analysis suggests that the asymmetric impacts of Arctic sea ice anomalies on subtropical North Pacific air-sea conditions and ENSO events may also be partly due to differences in the atmospheric mean state between high and low SIC years. This study highlights the asymmetric impact of Arctic SIC anomalies on ENSO and tropical climate, emphasizing the need to consider these asymmetries when assessing global climate responses to Arctic sea ice variability.