Vertical circulation in the tropical atmosphere during extreme El Niño-Southern Oscillation events

Abstract

Scenarios for the development of large-scale vertical circulation anomalies during warm and cold phases of El Niño-Southern Oscillation are generalized based on the NCEP/NCAR reanalysis data for . Composite models of the cells of vertical circulation in the monsoon and trade-wind regions of the tropical Pacific are obtained for the first time for El Niño and La Niña separately. An unprecedented shift of the ascending branch of the zonal Walker circulation from the "maritime continent" of Indonesia to the east, to the central and eastern Pacific, was observed during the warm phase over the tropical Pacific; this shift was accompanied by an abrupt increase in the tropical cyclogenesis activity in the southern Pacific zone of convergence. On the contrary, during the cold phase, the ascending motions in the region of the summer Australian monsoon are subject to abrupt intensification. The reconstruction of the vertical meridional circulation during the warm phase manifested itself in the almost complete disappearance of the Hadley classic circulation over the central Pacific, characteristic of the trade-wind intertropical convergence zone (ITCZ), and in its replacement by the latitudinal monsoon circulation typical of the ITCZ over the Indian Ocean. During a cold phase, the Hadley circulation is both restored and intensified.

Late-Holocene climatic variability indicated by three natural archives in arid southern Australia

“…The SWW is a strongly zonal atmospheric circulation pattern affecting the climate of Southern Hemisphere landmasses below ~30°S, bringing cooler seasonal (winter) rain to southern Australia (Fletcher and Moreno, 2012; Sturman and Tapper, 2006). The frequency of ASM incursions into the region is related to the ENSO phenomenon, with La Niña conditions producing a more intense ASM that can cause heavy rainfall across the continental interior (Semenov et al, 2008), while El Niño conditions result in more arid conditions in the region (Dai and Wigley, 2000). Indeed, the wettest year on record in Australia (1974) was a La Niña year and resulted in substantial filling of Lake Eyre, Lake Frome and Lake Callabonna, the latter filling to a depth of ~1 m. Historically, widespread, large-magnitude flooding has generally occurred across eastern and central Australia during La Niña phases, causing large flows in ephemeral streams within the Flinders Ranges (Quigley et al, 2010).…”

Holocene climate change in arid Australia from speleothem and alluvial records

“…Ashok et al, 2003;Evans et al, 2009;Ummenhofer et al, 2009), however several authors have proposed teleconnections amongst the IOD, ASM, ENSO, and SAM (e.g. Behera et al, 2006;Carvalho et al, 2005;England et al, 2006;L'Heureux and Thompson, 2006;Semenov et al, 2008;Suppiah, 1992;Wright, 1997). For example, Semenov et al (2008) used composite atmospheric circulation models to demonstrate that during La Niña ascending motions in the region of the Figure 6.…”

“…Behera et al, 2006;Carvalho et al, 2005;England et al, 2006;L'Heureux and Thompson, 2006;Semenov et al, 2008;Suppiah, 1992;Wright, 1997). For example, Semenov et al (2008) used composite atmospheric circulation models to demonstrate that during La Niña ascending motions in the region of the Figure 6. Correlative plot of various climate proxies, paleoclimatic interpretations and inferred temporal variability in ENSO intensity.…”

The use of integrated circulation index for the description of synoptic situations in the Pacific Ocean tropics during El Niño-Southern Oscillation extreme events

“…Within this work, the compositional fields of the most significant characteristics of atmospheric circulation have been already obtained separately for El Niño and La Niña events, and the synoptic mechanism of formation of westerly anomalies in subequatorial Pacific is proposed [9,11,13].…”