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 Perú-during three recent El Niño events: 1983, 1998, and 2016. Although these three events were the strongest El Niños, the different sources of moisture contribute to different rainfall patterns between El Niño 1983–1998 and 2016. In the region, the spatial pattern of precipitation during El Niño 2016 presents an unprecedented out-of-phase atmospheric response consistent and verified with water vapor transport when compared with El Niño 1983–1998. During El Niño 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 Niño, 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 Niño 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 Niño events.
Highlights
El Niño corresponds to a global scale climate pattern that is commonly observed in sea surface temperature (SST) anomalies in the Central Pacific Ocean [1,2,3,4,5,6]
The EP precipitation pattern expands over the Eastern Pacific near the edge of Ecuador and northern Perú, with northwesterly Q anomalies flux and positive rainfall anomalies consistent with other studies [33,47]
This study evaluates whether moisture transport from the Amazon could be responsible for extreme rainfall in both the Eastern Pacific (EP) basin and the Andes-in the tropics of Ecuador and extreme rainfall in both the Eastern Pacific (EP) basin and the Andes-in the tropics of Ecuador and northern Perú
Summary
El Niño corresponds to a global scale climate pattern that is commonly observed in sea surface temperature (SST) anomalies in the Central Pacific Ocean [1,2,3,4,5,6]. In the Andes, along the vicinity of northern Perú and Ecuador, the variability of rainfall (dry and wet) during El Niño years is related to remote moisture from the Pacific Ocean and by moist air from the Amazon basin [14,15,16] This claim has been controversial for years [16,17] (atmospheric subsidence in the Amazon basin constitutes a common pattern during El Niño years [18]). The transport of water vapor from the ocean and local topography of the Andes could lead rainfall production toward the continent [19,20] when land-sea breeze intersects the coastal area [9,11] Evidence of this source of moisture from the Amazon has been limitedly explored [21], so this study investigates whether this moist transport could have occurred during El Niño 2016.
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