Characteristics of the Dominant Frequency of West Pacific Warm Pool Subsurface Temperature in Response to ENSO Events.

Abstract:

West Pacific Warm Pool (WPWP) is the warm water body confined by Sea Surface Temperature (SST) over 28°C. The most important role of WPWP in response to air-sea interactions is that El-Niño and La-Niña events are determined by WPWP’s zonal migration. Many researches have conducted to understand the relationship between ENSO events and WPWP changes, but research for Subsurface Temperature (ST) fluctuation by WPWP’s movement does not well understood due to deficiency of observations, which is the main motivation of this research.

This research based on ARGO’s float profile subsurface data and TAO/TRITON’s mooring subsurface data. Especially, our research results are based on ST from surface to 500m depth and estimated ST deviation in route of eastbound WPWP between north and south 10° by the Pacific equatorial line to identify ENSO events. The El-Niño and La-Niña events were defined by Multivariate ENSO Index (MEI) and then, we computed certain frequencies of ST under each condition, respectively. In order to understand the dominant frequency of ST, Ensemble Empirical Mode Decomposition (EEMD) was used. EEMD is analysis method to add Gaussian white noise in signal to redeem weak point of analysis method to non-linear and non-stationary signal. The research result shows that during normal condition, ST deviation values in Eastern Pacific (EP) had lower than those of Western Pacific (WP). During El-Niño condition, ST deviation values in the EP was higher than the normal condition, and ST deviation values in the WP was lower than normal condition and higher frequency in temperature fluctuation. During La-Niña condition, EP had similar ST amplitude with normal condition, but ST deviation values in the WP was so lower than the normal condition and fluctuation frequency was lower, too. So, we could understand that our estimations are resulting from intensified ST difference between high temperature of WPWP and low temperature of subsurface in location of WPWP during El-Niño and La-Niña condition. In addition, ST fluctuation at different depths show that El-Niño events occur at relatively higher frequencies than La-Niña events.