Systematic improvement in simulated latent and sensible heat fluxes over tropical oceans in AMIP6 models compared to AMIP5 models with the same resolutions

Abstract

Recent studies have shown that most Atmospheric Model Intercomparison Project (AMIP5) models that participated in the fifth phase of the coupled model intercomparison project (CMIP5) overestimate surface latent (QLH) and sensible (QSH) heat fluxes over tropical oceans. This study aims to quantify and understand any improvement in simulated QLH and QSH in AMIP6 models compared to AMIP5 models with the same horizontal resolutions. To accomplish this, we compare the Ocean Atmosphere air-sea Flux (OAFlux) dataset to nine AMIP5 and nine AMIP6 models integrated over 30 years (1979–2008). We found that all the AMIP5 and AMIP6 models overestimate both components of fluxes, but all of the AMIP6 models performed better than their AMIP5 counterparts over the tropical oceans (30°S-30°N). Yet, systematic spatial biases remain, which leads to only a small improvement in the simulated fluxes. For example, the root mean squared error (RMSE) and mean bias in QLH in AMIP5 are 30 and 21 W m−2 compared to 28 and 19 W m−2 in AMIP6. This is an improvement of 2 W m−2 for both RMSE and bias in QLH, yielding a reduction in QLH bias by 10% and RMSE by 7%. For QSH, an improvement of 1 W m−2 is seen in both bias and RMSE, yielding a reduction in QSH bias by 25% and RMSE by 13%. The primary reason for the improvement in QLH in AMIP6 is the better representation of the 10m wind speed and air-sea humidity difference than those in AMIP5. The improvement in QSH is due to an improvement in air-sea temperature difference. These results offer guidance to the modeling community to improve model simulation of near-surface meteorological variables in the tropics.