Causes and impacts of sea ice variability in the sea of Okhotsk using CESM-LE

Abstract

This study provides a holistic view of the coupled ocean-atmosphere-sea ice processes responsible for generating interannual variability in sea ice coverage in the Sea of Okhotsk as well as the atmospheric response to this variability. Simulations from the Community Earth System Model Large Ensemble project are analyzed, providing the ability to elucidate the time evolution of these relationships through weekly lead-lag composite analysis, while maintaining a large number of samples to provide robust conclusions. We find that thermodynamic processes involving anomalous ocean-atmosphere heat fluxes affect the timing of initial sea ice growth in the Sea of Okhotsk as early as November. Low-level wind anomalies in the winter affect the extent to which sea ice fully develops, both through advection of the sea ice itself and through changes in the transport of air masses over the Sea of Okhotsk. In this study, the results synthesize and support a diverse set of mechanisms identified in previous observational studies to be responsible for anomalous sea ice conditions, but in a coupled global climate model framework with a large sample size. We also find evidence that anomalous ocean-atmosphere heat fluxes in the winter can trigger an atmospheric response comprised of a local negative sea-level pressure anomaly and Rossby wave that extends over North America. The sign of the turbulent heat fluxes relative to the sea ice anomalies confirm that this is indeed a lagged response of the atmosphere forced by sea ice anomalies. This validates the Rossby wave train response identified in more idealized model simulations with prescribed sea ice and sea surface temperature by demonstrating that this process also occurs in a more realistic coupled model framework.