Role of the SST coupling frequency and intra-daily SST variability on ENSO and monsoon-ENSO relationship in a global coupled model

This work is focused on the impact of diurnal SST coupling and ocean vertical resolution on the coupled simulation of El Niño-Southern Oscillation (ENSO) and its relationship with the Indian Summer Monsoon (ISM). To do so, we have analyzed model outputs from four long integrations of a relatively high resolution Coupled General Circulation Model (CGCM, e.g. SINTEX-F2). The only differences between the four integrations are the frequency of coupling between the ocean and atmosphere for the Sea Surface Temperature (SST) parameter (2 vs 24 hours coupling) and/or the vertical resolution (31 vs 301 levels) in the ocean component of the CGCM. Surprisingly, when 2 hours coupling for SST is implemented in the CGCM, the model's El Niño has a more realistic evolution in its developing and decaying phases, a stronger amplitude and a shift to lower frequencies when a 2 hours coupling strategy is implemented without any significant changes in the basic state of the CGCM. Furthermore, the ISM-ENSO teleconnection is better represented, particularly, the complex lead-lag relationships between the two phenomena, in which a weak ISM occurs during the developing phase of an El Niño event in the Pacific, are closely resembling the observed ones. Evidences will be presented to show that these improvements are only related to changes in the characteristics of the model's El Niño. The time scale interactions explaining these modifications of the simulated tropical variability in the CGCM will be finally documented.