Mechanisms and Sources of Predictability of the North Pacific Warming in the Late 1980s and Early 1990s

The late 1980s and early 1990s warming of the North Pacific Ocean was a significant climate event that coincided with the strong La Niña of 1988/89.  The UK Met Office's decadal prediction system, DePreSys, shows evidence of skill for this event. The mechanisms responsible for the warming event, and sources of predictability, are being investigated. The interaction between the tropical oceans and the North Pacific atmosphere has been examined using experiments with an Atmospheric General Circulation Model. Results indicate atmospheric conditions over the North Pacific during winter 1988/89 were forced by tropical SST anomalies associated with La Niña, and that the North Pacific SST was a source of damping. The role of the eruption of El Chichón in April 1982 has also been assessed using coupled model simulations: there is evidence that the eruption contributed significantly to the cooling that preceded the warming event. These results are being used assess, at a process level, the performance of DePreSys in the North Pacific region. We will report our most up to date results at the time of the conference.