It takes Two to Tango: How the interaction between the AMOC and the NAO influences decadal predictions over Europe

Speaker: Rein Haarsma, R&D Weather and Climate Modelling, KNMI

Although short to medium range weather forecasts have improved considerably over the last decades, seasonal up to decadal forecasts have up to now hardly any skill, especially in the midlatitudes. Potential skill for those longer forecast periods is related to the memory of slow components of the climate system such as the ocean.

For the Atlantic Ocean the most dominant mode of variability on longer time scales is the Atlantic Meridional Overturning Circulation (AMOC) that transports larges amount of heat poleward. It is therefore a potential source of forecast skill on seasonal to decadal time scales.

In the atmosphere the dominant mode of variability over the North Atlantic is the North Atlantic Oscillation (NAO), that has a large impact on the weather of Western Europe especially during winter.

In this colloquium I will argue that up to now due to biases and unresolved processes in ocean and climate models, the interaction between AMOC and NAO is not well simulated by those models and therefore has hampered potential forecast skill on seasonal to decadal time scales.

Bio: Rein Haarsma has been a senior research scientist at the KNMI from 1981 till his retirement in 2022. After his retirement until now he has assisted the KNMI in the development of climate information for the Dutch Caribbean islands. Since 2023 he is affiliated with the Barcelona Supercomputing Center. He was a lead author of the 6th assessment report of IPCC. His expertise is on climate variability and climate change with a focus on atmosphere-ocean interactions.

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