Effects of two different La Niña types on the South American rainfall

Abstract

The paper tests if the two La Niña (LN) types can be distinguished from each other using their climate impacts on northeastern Brazil (NEB). To this end, all LN events during the 1901–2010 period followed by a wet or dry rainy season (from February to April) in NEB are classified into two categories: WET‐LN and DRY‐LN. The global and regional anomalous atmospheric circulation patterns and the rainfall anomaly patterns in South America associated with the two cases are analysed. The WET‐LN and DRY‐LN events present, respectively, the eastern Pacific LN and central Pacific LN sea surface temperature (SST) anomaly features in the tropical Pacific. On the other hand, the WET‐LN features an interhemispheric SST dipole pattern in the tropical Atlantic, and the DRY‐LN, colder‐than‐normal surface waters in the tropical South Atlantic (TSA) and equatorial Atlantic during MAM(+1). The two analysed cases show regional differential circulation patterns in all seasons. The anomalous wetness over northern and northwestern South America occurs for the WET‐LN type during JJA(0)–DJF(+1) and for the DRY‐LN type, during DJF(+1)–MAM(+1). The anomalous dryness over SESA is more evident for the WET‐LN during JJA(0) and MAM(+1), and for the DRY‐LN, during SON(0). Anomalous dryness occurs in central and eastern South America noted during JJA(0) and DJF(+1) for both cases analysed. The precipitation anomalies in northern South America during DJF(+1) are stronger and more extensive for the DRY‐LN than for the WET‐LN events due to the action of both the anomalous (double) Walker and Hadley cells for the DRY‐LN, in contrast with the exclusive action of an anomalous Walker cell for the WET‐LN case. Also, a double Walker cell drives the dry–wet dipole between northern South America and NEB during MAM(+1) for the DRY‐LN. Our results might be useful mainly for climate monitoring purposes.

Dispersion of Smoke Plumes over South America

“…Using the times series of southern Amazon CO for July-October 2000-18, it is evident from the field correlation maps (Figs. 4d-f) that cooler sea temperatures and higher pressure in the east Pacific Ocean enhance fire emissions, consistent with La Niña (Andreoli et al 2018). 500-hPa zonal wind correlations indicate westerlies (1r) over Peru and easterlies (2r) over Brazil: opposing flows that confine the smoke plumes.…”

Influence of the modes of climate variability in the Tropical Pacific and Atlantic on accumulated rainfall and reservoir water volumes in the Northeast Brazil

“…According to Andreoli et al . (2019) the years 1989 and 2008 were classified as wet La Niña years, when La Niña events are followed by anomalous wetness during the rainy season. The authors also reported that during wet La Niña events the negative SST anomalies in the eastern Tropical Pacific propagate westward during the development and maturing of the phenomenon.…”

The role of the Atlantic Multidecadal Oscillation precondition in the teleconnection of different El Niño‐Southern Oscillation types and impacts on the 15°N–15°S South American sector precipitation

“…In fact, the descending anomalous motions occur in the 165°E–130°W and 20°–0°W bands, and around 80°W, and the ascending ones in the 120°–160°E and 70°–50°W bands (Figure f). It should be noted that a double Walker anomalous cell is a characteristic of the events CPLN (Xu et al ., ; Andreoli et al ., ). During D(0)JF(+1) in the CAMO, the anomalous Walker circulation weakens in relation to that of the WAMO and the double Walker cell is established (Figure e,g).…”