Atmospheric centres of action associated with the Atlantic ITCZ position

Abstract

ABSTRACT:Relationships between Atlantic extra-tropical features and Intertropical Convergence Zone (ITCZ) position close to Northeast Brazil are discussed, on the basis of atmosphere and ocean patterns in DJF and April. Composites for three situations were analysed. In the first composite, years with extreme positive North Atlantic Oscillation Index (NAOI) in DJF and the ITCZ displaced southward in April were selected. The other two composites were related only to anomalous ITCZ positions -either south or north of the equator -in April. The physical mechanism for the relation between the NAOI and the ITCZ is the influence of the southern North Atlantic Oscillation (NAO) centre on the North Atlantic subtropical high, the sea surface temperature (SST) and the intensity of the trade winds; however, this situation occurred in only a few years. Analysis of the other situations indicated the influence of a dominant mode of variability over the North and South Atlantic Oceans that affects the ITCZ position. Over the North Atlantic, this mode was related to a shifting of the NAO pattern, which modified the position of the North Atlantic subtropical high. Over the South Atlantic, this mode indicated an extra-tropical centre of action associated with displacement of the South Atlantic subtropical high. A proposed index for monitoring ITCZ position, named the North Atlantic Index (NAI), was calculated from sea level pressure (SLP) anomalies in the two centres of action of the North Atlantic in DJF, which are related to the shifting of the NAO. Although the NAO index is related to atmospheric/oceanic features associated with ITCZ displacement, the new index presented higher and more organized correlations with atmospheric and oceanic conditions linked to ITCZ behaviour and can be useful even when the NAO is not extreme.

Maximum covariance analysis to identify intraseasonal oscillations over tropical Brazil

“…1 are also in agreement with previous studies (Souza and Cavalcanti 2009;Alvarez et al 2014;Tomaziello et al 2015), which show that the MJO is the main intraseasonal variability pattern at play in South America, during the austral summer and fall.…”

On the opposite relation between extreme precipitation over west Amazon and southeastern Brazil: observations and model simulations

“…In 2008-2009 there was a premature onset of the rainy season over northern and NW Amazon that was related to the increase of moisture flux from the tropical North Atlantic, an intense Chaco low and a southward ITCZ displacement Satyamurty et al, 2013b). The influence of the ITCZ meridional displacement on intense rainfall and flooding in the Amazon region, in 2009, was also shown by Cavalcanti (2012), in which extratropical North Atlantic features were identified, similar to the analyses of Souza and Cavalcanti (2009). The subtropical North Atlantic high was more intense and favoured the southward displacement of trade winds and the ITCZ.…”

Reconstructing high-resolution climate using CT scanning of unsectioned stalagmites: A case study identifying the mid-Holocene onset of the Mediterranean climate in southern Iberia

“…The contrast between winter and summer precipitation in Iberia is due largely to the tendency for the NASH to migrate northwards over Iberia in summer (resulting in hot, dry conditions) and to migrate southwards in winter (bringing increased rainfall with the westerlies) (Harding et al, 2009;Trigo et al, 2004). In the present day, interannual variability in the strength and position of the NASH is linked to the state of the North Atlantic Oscillation (NAO) (Souza and Cavalcanti, 2009).…”