Seminars

10 am Friday 29 October 2010, Seminar room M345
School of Mathematical Sciences Seminar
Transition-phase climate regimes and teleconnections
Dr Shih-Yu (Simon) Wang (Utah Climate Centre)

Oscillatory climate modes provide an optimistic implication on the predictability of weather and climate. Over the Western Pacific and the Indian Ocean, the most pronounced of such climate modes include the MaddenJulian Oscillation (MJO), the El Nio-Southern Oscillation (ENSO), and the (quasi-)decadal oscillations. The teleconnectional impact of such climate modes has been extensively studied, mostly on the relationship between phases of the extreme positive/negative (or warm/cold) and regional climate anomalies. In this talk, evidence of the atmospheric teleconnection induced during the "transition phases" (i.e. between warm and cold) of certain oscillatory modes is presented. Such transition-phase teleconnections have a greatearound the world than the extreme phases would have.

Details about a transition-phase teleconnection of the Pacific quasi-decadal oscillation (QDO) are discussed. In the warm and cool phases of the Pacific QDO, the sea surface temperature (SST) patterns resemble those associated with ENSO. During the warm-to-cool and cool-to-warm transitions of the Pacific QDO, recurrent SST patterns are also clearly visible. The rotated empirical orthogonal function analysis shows that, while the warm-/cool-phase Pacific QDO generates an ENSO-like circulation pattern, the transition phases form a distinct short-wave train emanating from Southeast Asia towards North America. This short-wave train is particularly robust in the water vapour flux and it has a profound impact on the American West. Diagnostic analyses indicate that this short-wave train is thermodynamically maintained and is likely forced by diabetic heating near Southeast Asia. Additional modulations on this short-wave train from forcing sources in the western and eastern tropical Pacific are also discussed.