Mr. Dix et Bg. Hunt, CHAOTIC INFLUENCES AND THE PROBLEM OF DETERMINISTIC SEASONAL PREDICTIONS, International journal of climatology, 15(7), 1995, pp. 729-752
An analysis has been performed of three simulations made by forcing a
global climatic model with observed sea-surface temperature and sea-ic
e distributions for the period 1979-1988. These simulations were start
ed from different years of an extended control run, otherwise all cond
itions were identical. The analysis concentrates on the regional and l
ocal differences in the simulations caused by chaos attributable to th
e differing initial conditions interacting with the non-linearities of
the model climatic system. Of particular interest is whether the pres
ence of sea-surface temperature variations in individual years is able
to overcome chaotic influences. This interest arises because of the i
ncreasing international appreciation that such temperature variations
provide the basis for the development of multi-seasonal prediction sch
emes. The analysis shows that between about 20 degrees N and 20 degree
s S a coherent climatic reponse is obtainable owing to the boundary va
lue forcing associated with the sea-surface temperature field. At high
latitudes the signal-to-noise ratio rapidly deteriorates. Even at low
latitudes, in a sensitive variable such as rainfall, chaos creates su
bstantial differences between the three simulations, except over the P
acific Ocean where a very coherent response is found. In general, over
land areas, even those within recognized regions of ENSO (El Nino-Sou
thern Oscillation) influence, the impact of chaos is much higher. Exam
ination of Pacific North American teleconnection patterns for 1988 rev
eals substantial differences between the three simulations, and the as
sociated impact on rainfall and surface temperatures over the North Am
erican continent. Agreement with observations ranges from rather good
to poor, indicating the need for multiple runs for any given situation
. Overall the results establish that sea-surface temperature variation
s can overwhelm chaos in appropriate circumstances and specific region
s. Importantly, this indicates that given accurate predictions of sea-
surface temperature anomalies a few seasons in advance, then model-bas
ed predictions will be possible over many regions of the world despite
the omnipresence of chaos.