The Development And Assessment Of A New Air-Sea Coupled Model ECHAM5-NEMO3.6

In this study,a new air-sea coupled model has been developed to explore the key physical processes responsible for the coupled model biases and to find ways to improve the model simulation.The new coupled model ECHAM5-NEMO3.6 is based on the 5th generation European Centre atmospheric model ECHAM5(European Center Hamburg model),oceanic model NEMO(Nucleus for European Modelling of the Ocean)version 3.6 developed by the European Consortium,and the coupler OASIS(Ocean Atmosphere Sea Ice Soil)version 3.It has been integrated for 700 years without climate drift.Model evaluation and analysis of model error have employed methods such as correlation analysis,spectral analysis,composite analysis and Taylor's diagram.Model assessment results show significant improvements of the ECHAM5-NEMO3.6 simulation regarding the fields such as sea surface temperature(SST)and surface ocean currents.The ECHAM5-NEMO3.6 can reproduce the interannual variability of tropical Pacific SST and the ENSO related air-sea response.Although the cold tongue simulation has been intensified in the ECHAM5-NEMO3.6,the scope and magnitude are less than those of the MPI-ESM.Statistical diagnosis indicates that cloud radiation feedback is the main reason that causes the SST biases.The net radiation biases over the tropical Pacific force out an anomalous Walker circulation,which results in strong easterly biases over the tropical Pacific.Thermal budget and air-sea momentum joint effects over the sea surface that leads to excessive cold tongue simulation.Statistical diagnosis also indicates that the cumulus convection is the main cause of model bias in precipitation.In order to improve the simulation quality of cumulus convection,five new cumulus schemes have been implemented in ECHAM5 to explore their applicability in climate simulation.Experiment results indicate that two updated TIEDTKE schemes produce the best overall simulation.The TIEDTKE-? scheme upgrades the simulation quality of surface winds and evaporation,and the TIEDTKE-? scheme improves precipitation and surface radiative fluxes simulation.These two optimum cumulus schemes have been implemented in the ECHAM5-NEM03.6 coupled model,and model integration has been carried out with the same experimental configuration of the control run.The TIEDTKE-? scheme has upgraded model simulation including SST and precipitation,while the TIEDTKE-? scheme only maintains the simulation improvements of summer precipitation and total radiative fluxes.Model biases increase in other aspects with the use of the TIEDTKE-? scheme.The TIEDTKE-I scheme improves the simulation precision of cloud radiation feedback through air-sea interaction,which betters the simulation in many aspects including the SST and its interannual variability.Thus,the TIEDTKE-? scheme turns out to be the relative optimum cumulus parameterization in the ECHAM5-NEM03.6.