Decadal changes of ENSO persistence barrier in SST and ocean heat content indices: 1958–2001

Abstract

Decadal changes of El Niño‐Southern Oscillation (ENSO) persistence barriers in various indices of sea surface temperature (SST) and ocean heat content (OHC) are examined in this study using observations and ocean data assimilation products for the period 1958–2001. It is found that the SST indices in the eastern and central equatorial Pacific exhibit very different decadal barrier variability. The variability is large for the eastern Pacific SST indices (NINO1+2 and NINO3) whose persistence barriers shifted abruptly in 1976/1977 and 1989/1990. In contrast, the central Pacific SST indices (NINO3.4 and NINO4) experienced little decadal barrier variability and have had their persistence barriers fixed in spring in the past four decades. The zonal mean OHC index averaged over the equatorial Pacific shows decadal barrier changes similar to those in the eastern Pacific SST indices and always leads the NINO3 SST barrier by about one season. It is noticed that the SST persistence barrier appeared first in the eastern Pacific before 1976/1977, first in the central Pacific between 1976/1977 and 1989/1990, and almost simultaneous in both the eastern and central Pacific after 1989/1990. These timings coincide with the westward propagating, eastward propagating, and standing pattern of ENSO SST anomalies observed in these three periods. These results suggest that ENSO SST anomalies in the equatorial Pacific can be considered to consist of two different processes: a central Pacific process whose phase transition (such as onset) and barrier always happen in spring, and an eastern Pacific process whose phase transition and barrier change from decade to decade and are influenced by changes in the mean thermocline depth along the equatorial Pacific.

Decreased Response Contrast of Hadley Circulation to the Equatorially Asymmetric and Symmetric Tropical SST Structures during the Recent Hiatus

“…It is seen that the variation of SES relates to a classical El Niño like pattern during period 1979-1998. By contrast, the maximal correlation center has shifted to the central Pacific during period 1999-2015, which is consistent with the result that the central Pacific El Niño (Yu and Kao 2007) is more frequent in recent decades. As to the SEA, there are significant negative correlations over the central Pacific but centered to the north of the equator during period 1979-1998.…”

Changes in the in-phase relationship between the Indian and subsequent Australian summer monsoons during the past five decades

“…The figure shows that SST anomalies in all four NINO regions maintained high persistence throughout the analysis period, except in the far eastern Pacific (NINO1+2) where the SST persistence dropped significantly from the mid 1970s to the early 1990s before returning to its previous strength. Our results are consistent with Yu and Kao (2007) who found the SST persistence barrier in the NINO1+2 region shifted from boreal spring to late summer during 1978-1988. They linked this barrier shift to changes of mean thermocline depth along the equatorial Pacific.…”

ENSO stability in coupled climate models and its association with mean state

“…Among others, Yu and Kao (2007) and Kao and Yu (2009) To better describe this phenomenon, Ashok et al (2007) proposed an El Niño Modoki index (EMI), which represents the SST difference between the central tropical Pacific and the eastern and western parts of the basin. The EMI derived from Argo is shown in Fig.…”