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Ocean Surface Topography from Space
MODOKALT: Dynamics of Modoki El Niño as inferred from altimetry - OSTST project 2013-2015


Boris Dewitte - (LEGOS)

  Katerina Goubanova
Séréna Illig
Lee Tong


MODOKALT: Dynamics of Modoki El Niño as inferred from altimetry - OSTST project 2013-2015
Sea Surface Temperature (Anomalies) during the peak phase of the "canonical" 1997 El Niño and the Modoki 2004 El Niño (HadISST data set). The thick orange line represents the 28°C isotherm and delimits the region of deep convection. Anomalies for the 1997 El Niño reach 5°C whereas they reach 1.8°C for the 2004 El Niño.
Recent studies report that two types of El Niño events have been observed (Ashock et al., 2007). One is the cold tongue El Niño or Eastern Pacific El Niño (EP El Niño), which is characterized by relatively large sea surface temperature (SST) anomalies in the eastern Pacific, and the other is the warm pool El Niño (a.k.a. 'Central Pacific El Niño' (CP El Niño) or 'El Niño Modoki'), in which SST anomalies are confined to the central Pacific. Whereas the former has been extensively studied, the mechanisms associated with the later remain unclear.

The objective of this proposal is to study the dynamics of this new flavour of El Niño referred in the following as Central Pacific El Niño or Modoki El Niño.

This issue is currently a major concern in the climate community because there is evidence that the frequency of occurrence of this type of event has increased in recent years (Lee and McPhaden, 2010; Takahashi et al., 2011) and that such tendency will amplify in a warmer climate (Yeh et al., 2009a). In addition recent studies suggest that the alternation of periods of high occurrence of Modoki El Niño and "traditional" El Niño is due to the different non-linear processes (asymmetry) associated to the two types of events. In particular, the "traditional" El Niño is characterized by a positive asymmetry in the Eastern Pacific, whereas the Modoki El Niño has a negative asymmetry in the central Pacific (Boucharel et al., 2009; 2011) which may lead to a different rectification process on the mean state resulting in changes in ENSO properties (Yu and Kim, 2011; Choi et al., 2011) as well as a distinct teleconnecion pattern in the Peru upwelling system.

This three-years project aims at taking advantage of the long-term altimetric sea-level data set (TOPEX/POSEIDON/JASON) as well as recent coupled model development to investigate the mechanisms associated to the Modoki El Niño (wave propagation, non- linearities and predictability) and its impact on the Peru upwelling system. In particular it is proposed to use sea level data combined to an intermediate complexity model of the tropical Pacific (named LODCA-QTCM) to document equatorial waves characteristics (at intra- seasonal and inter-annual frequencies) and non-linearities associated to Modoki-type event and to improve seasonal forecasts over the period characterized by high-occurrence of this type of event (2000-2012).

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