The importance of eddy permitting model resolution for simulation of the heat budget of tropical instability waves

The heat budget of the eastern tropical Pacific Ocean is analysed in the global NEMO model at 1° and 0.25° resolution. The meridional component of heating of the equatorial cold tongue by tropical instability waves (TIWs) is 37% larger in the higher resolution model and in better agreement with observational estimates. During La Niña and neutral conditions the difference is more pronounced and meridional heat transports by TIWs in the 0.25° model are 74% larger than in the low resolution model. During El Niño the difference between the models is much smaller. There is less difference between the resolutions in simulation of the zonal component of the heating by TIWs. The results suggest that TIWs in the higher resolution model help to warm the equatorial cold tongue during La Niña events reducing the equatorial cold tongue bias and improving the simulation of the asymmetry of the ENSO cycle. Further, it is suggested that the currently available observational estimates of TIW heat budget contributions may be an underestimate as they cover a period dominated by El Niño or neutral conditions and do not include a La Niña event.