The impact of the tropical Indian Ocean sea surface temperature forcing on an upward trend of Arctic Oscillation

Abstract:

The Arctic Oscillation (AO), which is the dominant atmospheric variability over mid-to-high latitudes in the Northern Hemisphere (NH) in the boreal winter, has large impacts on the surface climate in the region such as East Asia and North America. The linear trend of the AO with global warming has been debated, and previous studies investigated its linear trend in a limited period. We investigate the linear trend of the AO in the long-term period from 1950s to the recent period using reanalysis and observation data. From the analysis, we find that the AO is dominant with a statistically significant upward trend. On the one hand, the AO in the model simulation using historical SST also has an upward trend, indicating an important role of SST forcing in an upward trend of AO. We examine the impact of the tropical SST forcing on the trend of the AO by conducting idealized experiments using an atmospheric general circulation model (AGCM) to investigate the impact of SST forcing in each tropical ocean basin. The historical SST from 1948 to 2018 is prescribed in the global ocean, the tropical Indian Ocean (IO), the western tropical Pacific (WP), the eastern tropical Pacific (EP) and the tropical Atlantic Ocean (AT), respectively, in each AGCM experiment. We find that the upward trend of AO is significant in the AGCM experiment where the historical SST is prescribed in the IO region only. We further examine the physical processes of how the Indian ocean SST forcings lead to an upward trend of AO.