Title: The Impact of Basic State on Quasi-Biennial Periodicity of Central Pacific ENSO over the Past Decade

Journal: Theoretical and Applied Climatology, 120: 55-67

Authors: XIE R. -H., F. Huang*, F. -F. Jin, and J. Huang

Abstract:El Niño/Southern Oscillation (ENSO) phenomenonlately appears to have a much fast pace with four warmingevents in the past decade (2002-2012). Three out of fourevents have their warming centers confined in the equatorialcentral Pacific. It is argued that the anomalous zonal seacurrents are responsible for the fast transition of the centralPacific warming. Furthermore, based on the heat budget analysis,it is found that zonal advective feedback appears to playan important role in the phase transition of central PacificENSO, although the thermocline feedback process that isessential for ENSO, as delineated by the recharge/dischargeoscillator theory, also contributes but mainly in the easternPacific. A stability analysis is performed using a simplestripped-down coupled model with two different basic statesettings derived from the periods over 1982-2001 and 2002-2012, respectively. In the two periods, the basic states showdifferent distribution along the equator and the leading ENSO-likeeigen-modes have very different periods and patterns. The mode under the basic state in the earlier period resembles theeastern Pacific ENSO with a period about 5 years, whereasunder the basic state in the recent decade, the ENSO modebecomes more like the observed central Pacific ENSO with aperiod about 2 years. The slow eastern Pacific ENSO mode isdominated by the thermocline feedback and behaves more likethe recharge oscillator, whereas the zonal advective feedbackplays a significant role in the fast-paced central Pacific ENSOmode. These results are roughly consistent with the broadfeatures of two types of ENSO. In addition, the zonal advectivefeedback contributes to the phase transitions of both typesof ENSO-like modes. In a word, the recent fast-paced ENSOactivities in the central Pacific is suggested due to the dominanceof zonal advective feedback favored by the tropicalPacific basic state conditions in the past decade.