[A-CG43] Multi-scale ocean-atmosphere interaction in the tropics

[ACG43-P03] The Role of Vertical Mixing in the Development of El Niño Modoki

*Tomoki Tozuka¹ (1.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo)

Keywords:El Niño Modoki, Vertical mixing, Mixed layer heat budget analysis

The El Niño/Southern Oscillation (ENSO) is the most prominent interannual climate mode, profoundly affecting global climate. This phenomenon exhibits remarkable diversity and is commonly classified into two groups based on the location of maximum sea surface temperature anomalies. One of the two flavors with the maximum anomalous warming in the central equatorial Pacific is called El Niño Modoki. It has been suggested that anomalous zonal advection primarily contributes to the development of the positive sea surface temperature anomalies. Using outputs from a realistic ocean model simulation, it is shown that anomalous vertical mixing makes a dominant or comparable contribution to the anomalous zonal advection during the development of El Niño Modoki in four out of six simulated events. Further analyses indicate that cooling by vertical mixing is reduced because weaker vertical shear between the surface westward current and the subsurface eastward current, which in turn reduces vertical diffusivity. Moreover, a relaxed vertical temperature gradient across the base of the mixed layer weakens the cooling effect of vertical mixing.