Ananya, K.; Anant, P.; Chowdary, J.S., and Gnanaseelan, C., 2020. Sensitivity of subsurface processes of equatorial Pacific Ocean to the heat and momentum fluxes: A case study of 1997-98 El Niño. In: Sheela Nair, L.; Prakash, T.N.; Padmalal, D., and Kumar Seelam, J. (eds.), Oceanic and Coastal Processes of the Indian Seas. Journal of Coastal Research, Special Issue No. 89, pp. 26-31. Coconut Creek (Florida), ISSN 0749-0208.

The influence of accurate heat and momentum fluxes on 1997-98 El Niño simulation is investigated using Geophysical Fluid Dynamics Laboratory (GFDL) ocean model Modular Ocean Model version 5 (MOM5). Control experiment (CTRL) is carried out by using surface forcing from the CORE2 inter-annual flux, whereas sensitivity experiment (OAERA) is carried out by using heat fluxes from WHOI Objectively analysed air-sea fluxes (OAFlux) data and momentum fluxes from ERA-interim (ERA-I). Both experiments are carried out for a common period of 1985-2009. These experiments revealed that the strength of inter-annual variability is sensitive to accuracy of the forcing. In particular, the sensitivity experiment displayed better simulation of 1997-98 El Niño features such as developing and peak phases. The strength of Niño indices (mainly Niño 3 and Niño 3.4) in OAERA is comparable to EN 4/ORAS 3 more than CTRL. Further analysis reveals that throughout the equatorial Pacific Ocean upper ocean temperature anomaly evolution during the developing to peak phase is improved in OAERA, which is further confirmed by the mixed layer temperature anomaly tendency (TAT) evolution. Detailed analysis of dynamical feedback contribution to TAT indicates that in CTRL, thermocline and zonal advection feedbacks are overestimated and their temporal evolution is inconsistent compared to ORAS 3, whereas these feedbacks are consistent in OAERA, leading to better simulation of Niño indices. Our study concludes that accurate heat flux and momentum flux forcing can improve the simulation of Niño indices and equatorial Pacific upper ocean temperature anomaly associated with the strong El Niño 1997-98.

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