Abrupt changes as indicators of decadal climate variability

A statistical test has revealed that abrupt regional climate changes are pr oduced in a coupled atmosphere-ocean general circulation model. Abrupt chan ges are detected over much of the globe although the occurrence frequency i s small over the continents. Over the tropical Pacific Ocean and northern P acific Ocean, surface air temperature (SAT) and sea level pressure (SLP) sh ift rapidly on decadal time scales. The regional climate changes presented here have been classified into three types. The first type consists of stat istically significant shifts in SLP and statistically significant shifts in SAT which are of opposite sign, and which are reinforced through a positiv e feedback between the atmosphere and the ocean. The second type is for tho se occurrences where changes are of the same sign. The third type includes those with a significant shift in only one meteorological element. The seco nd and third types are generally generated by changes in air pressure and w ind fields induced by changes of the first type. For example, when SLP incr eases and sea surface temperature (SST) decreases abruptly in the tropical Pacific Ocean, it triggers abrupt regional changes in middle and high latit udes. The abrupt changes in the model climate have characteristics which ar e very similar to those of observed rapid shifts. Thus, it is concluded tha t abrupt changes are a predominant part of regional climate change on decad al time scales.