Can Ningaloo Niño develop without ENSO? — Australian Meteorological and Oceanographic Society

Can Ningaloo Niño develop without ENSO? (#33)

Takahito Kataoka 1 , Sébastien Masson 2 , Takeshi Izumo 2 , Tomoki Tozuka 3 , Toshio Yamagata 1
  1. JAMSTEC, Yokohama, KANAGAWA, Japan
  2. LOCEAN, Paris, France
  3. The University of Tokyo, Tokyo, Japan

Ningaloo Niño/Niña is the dominant climate mode in the southeastern Indian Ocean with its center of positive/negative sea surface temperature anomalies attached to Australia and Ningaloo Niño is the major cause of marine heatwaves in the region. Although oceanic variability in this region has long been considered to be mainly a response to the El Niño–Southern Oscillation (ENSO), some recent studies have suggested the possible existence of local air-sea feedback processes. Thus, Ningaloo Niño/Niña may develop without ENSO. However, as long as ENSO exists (it does in the real world), ENSO influence including its delayed effects, which is nonlinear, cannot be completely removed from the observational data. Therefore, the observational fact of neither the co-occurrence with El Niño and La Niña nor the low correlation coefficient with an ENSO index provides a definitive answer to the above question. Using a state-of-the-art ocean-atmosphere coupled model that realistically simulates Ningaloo Niño/Niña, whether Ningaloo Niño/Niña can occur independently of ENSO is examined. Even in an experiment in which ENSO is suppressed by strongly nudging tropical Pacific sea surface temperatures toward the model climatology, Ningaloo Niño/Niña with a similar magnitude, duration, and seasonality still develops, likely through an air-sea interaction off Western Australia amplifying atmospheric stochastic forcing. This study is the first to show that Ningaloo Niño/Niña can develop even without ENSO.

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