18th Conference on Climate Variability and Change


Harbingers for La Nina and El Nino events


Wilbur Y. Chen, NOAA/NWS/NCEP/CPC, Camp Springs, MD

The conventional understanding of an ENSO life-cycle is a cold-phase development following the demise of a warm phase, thus completing a whole life cycle. Recent examination of the observed data indicates that the mechanisms leading to an ENSO life-cycle can be severed into two parts: warm and cold event, separately. Each cold or warm event can be initiated randomly without one event following the other. Each event has its own beginning and ending. In other words, each event leads its own life, without requiring an interaction between the two. Most interestingly, each event has its own precursor. And, the structures of these two precursors are distinct. The physical process acting on buildup phase is found also working for an occasional re-strengthening of the same episode without going through a change of phase of a conventional ENSO life-cycle. These precursors, which can be found in the normalized sea-level pressure anomalies, complement those already found in the sub-surface heat contents, providing additional valuable physical understanding as to how a La Nina event, as well as an El Nino event, is initiated and strengthened, and sometimes, re-strengthening itself before a complete demise. Examples of such cases occurred during 1973 to 1976 for a prolonged cold episode and 1990 to 1995 for a prolonged warm episode.

Poster Session 2, Observed seasonal to interannual climate variability and climate applications
Wednesday, 1 February 2006, 2:30 PM-4:00 PM, Exhibit Hall A2

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