The evolution of tropical and extratropical precipitation during ENSO events

Many studies have tried to relate ENSO and global precipitation. This work examines changes in precipitation pattern, amount, and intensity during ENSO events over the past 20+ years, using satellite-gauge merged data sets. ENSOs vary in duration and may peak at different times of the year. In this way, compositing events into seasons, such as onset, mature, and decay, is a challenge. This study will explore the sensitivity of using fixed versus variable month seasons to describe El Niños and La Niñas. Global precipitation patterns will be shown. Both increases and decreases in rainfall are observed during ENSO, and there are more extreme and less "normal" rain rates (i.e. a greater occurrence of drought and flood) in space and time. In the Southern Hemisphere during ENSO there is a spiral pattern of precipitation anomalies, centered at the pole, that agrees with previous studies looking at model-generated surface pressure. This study also examines the evolution of precipitation and SST in the tropical Pacific. The relation between the Maritime Continent convection center and the underlying surface temperatures of the islands will also be explored. An examination of the evolution of the 1997-98 El Niño and accompanying precipitation anomalies revealed that a dry area surrounding Indonesia, preceded the formation of positive SST anomalies in the eastern Pacific Ocean. 30-60 day oscillations in the winter of 1996/97 may have contributed to this lag relationship. A similar time line of onset was observed during the 1982-83 El Niño. These two events were comparable in strength and timing during the annual cycle. However, in the 1982-83 event the warming at the surface first appeared in the central Pacific, whereas in the 1997-98 event the warming first emerged off the coast of Peru. In both events the positive precipitation anomalies were first observed in the central Pacific, moving to the east Pacific within a month or two.