Unprecedented rainfall and moisture patterns during el nino 2016 in the eastern pacific and tropical andes: Northern peru and ecuador

Abstract

Using vertically integrated water vapor and its convergence, associated with large-scale and regional atmospheric circulation, we found two patterns of rainfall over the Eastern Pacific (EP) and the tropical Andes-with a focus in Ecuador and northern Peru-during three recent El Nino events: 1983, 1998, and 2016. Although these three events were the strongest El Ninos, the different sources of moisture contribute to different rainfall patterns between El Nino 1983-1998 and 2016. In the region, the spatial pattern of precipitation during El Nino 2016 presents an unprecedented out-of-phase atmospheric response consistent and verified with water vapor transport when compared with El Nino 1983-1998. During El Nino 2016, precipitation in the Andes was enhanced by moist air transported from the Amazon-with an opposite regime compared to the subsidence that dominated in 1983-1998. During the 1983-1998 El Nino, the source of moisture to feed the EP was enhanced by upper-level divergence (300 hPa), which supports moisture influx by middle levels in the EP. In El Nino 2016, this divergent upper-level flow migrated north, followed by the companion moisture. This study illustrates a link between upper-level large-scale circulation and low-level regional mechanisms on the moisture transport in determining different rainfall patterns during El Nino events.