Datensatz

Zusammenfassung

The impact of initial conditions relative to external forcings in
decadal integrations from an ensemble of state-of-the-art prediction
models has been assessed using specifically designed sensitivity
experiments (SWAP experiments). They consist of two sets of 10-yr-long
ensemble hindcasts for two initial dates in 1965 and 1995 using either
the external forcings from the "correct" decades or swapping the
forcings between the two decades. By comparing the two sets of
integrations, the impact of external forcing versus initial conditions
on the predictability over multiannual time scales was estimated as the
function of lead time of the hindcast. It was found that over time
scales longer than about 1 yr, the predictability of sea surface
temperatures (SSTs) on a global scale arises mainly from the external
forcing. However, the correct initialization has a longer impact on SST
predictability over specific regions such as the North Atlantic, the
northwestern Pacific, and the Southern Ocean. The impact of
initialization is even longer and extends to wider regions when
below-surface ocean variables are considered. For the western and
eastern tropical Atlantic, the impact of initialization for the 700-m
heat content (HTC700) extends to as much as 9 years for some of the
models considered. In all models the impact of initial conditions on the
predictability of the Atlantic meridional overturning circulation (AMOC)
is dominant for the first 5 years.