Assessing the Representation of Intraseasonal Oscillation-Related Ocean Forcing in the Tropics in Atmospheric Reanalyses

Abstract

Previous studies suggest the nature of the air–sea interaction of the tropical intraseasonal oscillation (ISO) can strongly influence our understanding and simulation of the ISO characteristics. In this study, we assess the representation of the surface components in three of the most up-to-date reanalyses, namely, the fifth generation of the European Centre for Medium-Range Weather Forecasts' (ECMWF) reanalysis (ERA5), ERA-interim (ERAi), and Japanese global atmospheric reanalysis (JRA55), to identify which reanalysis dataset is more suitable for investigating air–sea interaction associated with the ISO and to quantify the intraseasonal biases of related variables for simulating the ocean responses. All three reanalyses well capture the ISO convective characteristics in terms of the spatial patterns and the propagation features, although the amplitude of the outgoing longwave radiation is severely underestimated (by ∼ 40–60 %, depending on region and season) in JRA55. Out of the two ERA reanalysis datasets, our results indicate the ERA5 may serve as a better ocean forcing dataset, as the ERAi largely underestimates the magnitudes of the ISO-related precipitation and 10 m winds (of summer ISO or boreal summer ISO) but overestimates the latent heat flux (of winter ISO or the Madden–Julian oscillation). JRA55, while having comparable amplitude biases to ERA5 in variables except precipitation, generally shows larger phase biases in comparison with the two ERA reanalyses.