Data: Linear Response Function Reveals the Most Effective Remote Forcing in Causing September Arctic Sea Ice Melting in CESM

We apply the linear response function to investigate the most excitable mode of the September Arctic sea ice in the Community Earth System Model. We find that this sea ice mode preferentially takes place over the Pacific side of the Arctic and its remote forcing corresponds to a dipole pattern of precipitation anomaly in the tropics with an increase of precipitation over the western and central tropical Pacific ocean while a decrease over the Maritime Continent. The tropical precipitation anomaly likely drives a Rossby wave train propagating toward the higher latitudes and leads to a ridge anomaly over the Pacific side of the Arctic, resulting in poleward atmospheric heat transport, enhanced downward longwave radiation and thus melting of the sea ice. In addition, a good agreement is found with the leading tropical-Arctic teleconnection mode in a pre-industrial simulation, supporting the usefulness and robustness of the linear response function method.