Diurnal cycle metrics for validating NWP and climate models and understanding air-sea interaction in the Tropical Pacific

Recent studies have increasingly demonstrated the importance of including diurnal cycles in the Numerical Weather Prediction (NWP) and coupled climate models. The inclusion of diurnal variability in the models has shown strong impacts on the response of sea surface temperature (SST) to intra-seasonal variability, the characteristics of the Madden-Julian Oscillation, the mean climate of both atmosphere and ocean, the amplitude of the ENSO cycle, and improved short and medium range model forecasts. Properly simulating the diurnal cycles in the numerical models is challenging due to the complex air-sea interaction processes involved. The variables near the air-sea interface experience different diurnal cycles, and yet they are tightly related through the air-sea coupling. Simulated diurnal cycles thus have a wide range of variations among different models. To aid the validation and improvement of the NWP and coupled climate models, as well as the satellite products likely biased by limited number of samplings throughout the day, diurnal cycle metrics have been calculated from the long timeseries of in situ measurements by the TAO/TRITON moored buoy array in the tropical Pacific. Diurnal cycle of all variables near air-sea interface will be made easily accessible to modelers and the scientific community; and will be presented here, including SST, sea surface salinity, wind, air temperature and humidity, precipitation, downward short and longwave radiation, and the derived sensible and latent flux, wind stress, net surface heat flux and skin temperature where possible. Significant changes of diurnal metrics between different climate regimes and modes of tropical Pacific variability will be discussed in the context of local and basin scale air-sea interaction and the Tropical Pacific Observing System (TPOS) – 2020 project that is evaluating and revamping the observing system with enhanced buoys and newer technologies.