Guest post by Bob Tisdale
The press release…
…for the Hye-Mi Kim, et al (2009) paper “Impact of Shifting Patterns of Pacific Ocean Warming on North AtlanticTropical Cyclones”…
…includes the quote from Peter Webster, one of the authors of the paper, “’Normally, El Nino results in diminished hurricanes in the Atlantic, but this NEW TYPE is resulting in a greater number of hurricanes with greater frequency and more potential to make landfall,’ said Peter Webster, professor at Georgia Tech’s School of Earth and Atmospheric Sciences.” (Caps added for emphasis.)
The press release continues, “That’s because this NEW TYPE of El Nino, known as EL NINO MODOKI (from the Japanese meaning “similar, but different”), forms in the Central Pacific, rather than the Eastern Pacific as the typical El Nino event does. Warming in the Central Pacific is associated with a higher storm frequency and a greater potential for making landfall along the Gulf coast and the coast of Central America.” (Caps added for emphasis.)
Hye-Mi Kim et al (2009) references (Their Reference 10) the Ashok et al (2007) paper “El Nino Modoki and its Possible Teleconnection.”
Ashok et al introduce a new index to document the occurrence of an El Nino Modoki event. They write, “Based on the EOF2 pattern presented in Figure 2b and the PC2 time series shown in Figure 3, we derive an El Niño Modoki index (EMI). Because of the unique tripolar nature of the SSTA, the index is defined as follows:
“EMI= [SSTA]A-0.5*[SSTA]B-0.5*[SSTA]C (1)
“The square bracket in Equation (1) represents the area-averaged SSTA over each of the regions A (165E-140W, 10S-10N), B (110W-70W, 15S-5N), and C (125E-145E, 10S-20N), respectively.”
The areas of the western, central, and eastern tropical Pacific included in the equation are illustrated in Figure 1.
Figure 2 is a short-term (1979 to 2008) times-series graph of the El Nino Modoki Index, using the calculation from Ashok et al. I’ve also standardized the data. Ashok et al define a typical El Nino Modoki event as, “We call an El Nino Modoki event ‘typical’ when its amplitude of the index is equal to or greater than 0.7α, where α is the seasonal standard deviation.” I’ve also highlighted 0.7 on Figure 2.
Figure 3 is a longer-term (1900 to 2008) times-series graph of the El Nino Modoki Index. As you will note, El Nino Modoki events as determined by the El Nino Modoki Index have occurred over the entire term of the data. There is nothing NEW about El Nino Modoki events.
HADISST data is available through the KNMI Climate Explorer website: