Speaker: Hemant Khatri (Met Office)
Title: An ocean memory perspective on decadal climate variability and simple climate models for global and regional future projections
Abstract: This talk will have two parts. In the first half, I will talk about an ocean memory framework to examine the atmosphere’s influence on driving decadal changes in ocean temperatures and to quantify ocean memory using the Green function’s approach.
The atmosphere and ocean are closely coupled and continuously interact through the exchange of momentum, heat and mass. The atmosphere changes much faster than the ocean due to their different timescales and the ocean’s ability to store excess heat for many years, commonly referred to as ocean memory. As a consequence, isolating and understanding how short-term atmospheric variations influence long-term fluctuations in the ocean, particularly on decadal timescales, can be difficult.
We show that the atmosphere alters the ocean state through two mechanisms: short-term, local effects involving air-sea heat fluxes and Ekman circulation, and long-term, far-field effects involving changes from overturning and gyre circulations. The ocean memory framework is employed to examine the North Atlantic Oscillation’s(NAO) influence on the North Atlantic Ocean variability. One of the key findings is that decadal fluctuations in ocean temperatures cannot be accurately modelled solely as a passive response to stochastic atmospheric forcing. This is because models that assume a passive ocean fail to capture the delayed, long-term changes in ocean circulation and the associated redistribution of ocean anomalies.
In the second half, I will talk about simple climate models or climate emulators, which are widely used to assess future projections for a much wider range of emission scenarios than covered in Earth system models. Given the computational efficiency of climate emulators, these can be used for analysing global and regional climate changes at high spatial resolution for a wide range of emission scenarios. I will present some specific examples.