Intraseasonal Tropical Atmospheric Variability Associated with the Two Flavors of El Niño

Abstract

The characteristics of intraseasonal tropical variability (ITV) associated with the two flavors of El Niño [i.e., the canonical or eastern Pacific (EP) El Niño and the Modoki or central Pacific (CP) El Niño] are documented using composite and regression analysis. Double space–time Fourier analysis is applied to the NCEP–NCAR zonal wind at 850 hPa (U850) to separate the different components of the ITV in the tropical troposphere, which is then used to define indices of wave activity, and document the spatial pattern of the waves. It is shown that the ITV characteristics are altered during CP El Niño compared to the typical seasonal dependence of the ITV–ENSO relationship. In particular, while EP El Niño is characterized by enhanced MJO and equatorial Rossby (ER) wave activity during spring–summer prior to the ENSO peak, during CP El Niño, the ITV activity is increased during the mature and decaying phases. It is suggested that ITV is more propitious to the triggering of the EP event; while during the CP event, it contributes mostly to the persistence of positive SST anomalies. The oceanic response of these ITV anomalous patterns is further investigated in the Simple Ocean Data Assimilation (SODA) reanalysis by documenting the seasonal evolution of the intraseasonal equatorial oceanic Kelvin wave (IEKW) activity during the two flavors of El Niño. It is shown that anomalous westerlies associated with ITV may generate the corresponding response in the ocean in the form of anomalous IEKW activity.

Contrasting Madden–Julian Oscillation activity during various stages of EP and CP El Niños

“…From 0 to 80 days, the MJO is as strong as that in the pre-developing period; while from 80 to 160 days, it becomes substantially suppressed. This feature is much more evident that in Gushchina and Dewitte (2012). During the mature and decaying stages, the MJO activities are enhanced.…”

The relationship between intraseasonal tropical variability and ENSO simulated by the CMIP5

“…While several studies suggest the predictive value of the ITV for ENSO (McPhaden et al, 2006;Hendon et al, 2007;Gushchina and Dewitte, 2011;Puy et al, 2015), Gushchina and Dewitte (2012) …”

Response of CO<sub>2</sub> and H<sub>2</sub>O fluxes in a mountainous tropical rainforest in equatorial Indonesia to El Niño events

“…Today, two types of ENSO can be distinguished: (1) the canonical or conventional El Niño, which is characterized by SST anomalies located in the eastern Pacific near the South American coast (Rasmusson and Carpenter, 1982), and (2) the central Pacific El Niño or El Niño Modoki (Larkin and Harrison, 2005;Ashok et al, 2007;Kug et al, 2009;Ashok and Yamagata, 2009;Gushchina and Dewitte, 2012). In 2003, a new definition of the conventional El Niño was accepted by the National Oceanic and Atmospheric Administration (NOAA) of the USA, in referring to the warming of the Pacific region between 5 • N-5 • S and 170-120 • W. According to Ashok et al (2007) the central Pacific El Niño, or El Niño Modoki, -i.e., unusually high SST -occurs roughly in the region between 160 • E-140 • W and 10 • N-10 • S.…”

“…Furthermore, MJO behavior varies significantly during the ENSO cycle: it is significantly decreased during the maxima in conventional El Niño episodes, while it is still active during the peak phase of central Pacific events. MJO rarely occurs during La Niña episodes (Gushchina and Dewitte, 2012). As MJO is strongly responsible for intra-seasonal variation of precipitation in the study region, the occurrence of MJO events was compared to the significant anomalies of the ET / P ratio and of key meteorological variables.…”