We have examined sources of SST drift in coupled forecast models that have provided data to the international S2S Database. Climatological SST drift (i.e., the November-April averaged change in mean state SST as a function of lead time, dSST/dt) was decomposed into one component correlated with the net surface heat flux (Qnet) and a second component associated with ocean processes. The Qnet-driven SST drift was estimated by regressing the climatological dSST/dt onto climatological Qnet; the ocean component of drift is the dSST/dt that is not correlated with Qnet, i.e., the residual. Maps of Qnet and ocean dynamics contributions to 30-day SST drift in S2S models shown in Fig. 3 reveal wide discrepancies in regional sources of SST drift among models. Lead-dependent time series of each term (not shown) sometimes reveals large initial contributions of Qnet or ocean dynamics terms that reflect initialization shock, whereas monotonic tendencies of each term over the 30-day forecast period reflect drift toward models’ preferred mean states.
The subsurface ocean features are important for air-sea interaction and have been shown to play important roles in the development of the El Nino events. The barrier layer and isothermal layer distribution across the Tropical Pacific and their evolution can play an important role in modulating air-sea interaction over the region and hence influence ENSO evolution. Hence, observing the variability of the barrier layer over the eastern edge of the warm pool region, mixing processes in the region and the variability and drivers of the barrier layer would be very informative to guide model development in improving these process representations.
Wei, H-H., A. C. Subramanian, K. Karnauskas, C. A. DeMott; M. R. Mazloff; M. A. Balmaseda, (2020): Tropical Pacific Air-sea Interaction Processes and Biases in CESM2 and their Relation to El Nino Development. J. Clim., sub judice.
Jiang, X., A. Adames-Corraliza, A., D. Kim, E. Maloney, H. Lin, H. Kim, C. Zhang, C. DeMott, and N. Klingaman, 2020: Fifty Years of Research on the Madden-Julian Oscillation: Recent Progress, Challenges, and Perspectives, Accepted to JGR Atmospheres.
Fredriksen, H-B., J. Berner, A. C. Subramanian, A. Capotondi (2020): How Does El Niño Southern Oscillation Change Under Global Warming – A First Look at CMIP6, GRL, 47, e2020GL090640. https://doi.org/10.1029/2020GL090640.
Karnauskas, K. B. (2021) A simple coupled model of the wind-evaporation-SST feedback with a role for stability. J. Climate, submitted.
Verdy, A., M. Mazloff, B. D. Cornuelle, A. C. Subramanian (2021) ENSO influence on heat and freshwater budgets in the tropical Pacific Ocean state estimate, to be submitted.
Data can be downloaded from the Tropical Pacific Ocean State Estimation website