The Years of El Niño, La Niña, and Interactions with the Tropical Indian Ocean

Abstract

The Indian Ocean zonal dipole is a mode of variability in sea surface temperature that seriously affects the climate of many nations around the Indian Ocean rim, as well as the global climate system. It has been the subject of increasing research, and sometimes of scientific debate concerning its existence/nonexistence and dependence/independence on/from the El Niño–Southern Oscillation, since it was first clearly identified in Nature in 1999. Much of the debate occurred because people did not agree on what years are the El Niño or La Niña years, not to mention the newly defined years of the positive or negative dipole. A method that identifies when the positive or negative extrema of the El Niño–Southern Oscillation and Indian Ocean dipole occur is proposed, and this method is used to classify each year from 1876 to 1999. The method is statistical in nature, but has a strong basis on the oceanic physical mechanisms that control the variability of the near-equatorial Indo-Pacific basin. Early in the study it was found that some years could not be clearly classified due to strong decadal variation; these years also must be recognized, along with the reason for their ambiguity. The sensitivity of the classification of years is tested by calculating composite maps of the Indo-Pacific sea surface temperature anomaly and the probability of below median Australian rainfall for different categories of the El Niño–Indian Ocean relationship.

Skill of ECMWF system‐4 ensemble seasonal climate forecasts for East Africa

“…As an example, 1982/83, and 1997/98 represent El-Niño years while 1983/84, 1988/89 and droughts of 1999 represent La-Niña years, agreeing with other studies (i.e. Camberlin and Philippon, 2002;Camberlin et al, 2001;Indeje et al, 2000;Meyers et al, 2007;Omondi et al, 2013).…”

Characteristics and variability of synoptic features associated with cool season rainfall in southeastern Australia

“…Both the El Niño and IOD+ composites (top row and right column in Figure 22) are marked by negative (cool) thickness anomalies over the Pacific Ocean east of Australia and in northeastern Australia. This is consistent with the cool sea surface temperature (SST) anomalies associated with this region for these categories (Meyers et al, 2007). By contrast, the IOD− and La Niña categories (left column and bottom row in Figure 22) show warmer thickness anomalies in this region and warm anomalies northwest of Australia.…”

“…Rainfall in the Australian region is strongly influenced by both the EI Niño/Southern Oscillation (ENSO) (Allan, 1988;Nicholls et al, 1997;Wang and Hendon, 2007) in the Pacific Ocean and the IOD (Ashok et al, 2003). Meyers et al (2007) have recently classified all years between 1885 and 1999 according to ENSO state (El Niño, neutral, La Niña) and IOD state (IOD+, neutral, IOD−). This classification defines a 3 × 3 matrix with years allocated to the appropriate cells of the matrix.…”

“…For the southeast Australia region, wet years in this classification generally correspond to combinations in which IOD is negative, and/or there is a La Niña. Dry years generally correspond to combinations in which IOD is positive and/or there is an El Niño (Meyers et al, 2007). Thickness anomaly composites for the ENSO/IOD year groupings are shown in Figure 22 for the winter season.…”

Impact of Surface Forcing on Southern Hemisphere Atmospheric Blocking in the Australia–New Zealand Sector

“…5a). Also featured were remnant anomalous cool SST in the Pacific Ocean following the La Niña of 1988 and the emergence of a negative Indian Ocean dipole event in 1989 (Meyers et al 2007). As such, the SST anomalies in the eastern Indian Ocean were characterized by a meridional SST gradient (Fig.…”