NEMS Mediator: Current Status and Ongoing Development

The NOAA Environmental Modeling System (NEMS) is a system infrastructure used for building a collection of modeling applications within a unified framework. It is based on the Earth System Modeling Framework (ESMF) and National Unified Operational Prediction Capability (NUOPC) layer software. The coupling of different model components is through a mediator component within NEMS. The roles of the mediator include field interpolation, field averaging, field merging, and custom air-sea flux calculations. NOAA is using this design architecture to build a Unified Forecast System (UFS) to provide guidance from weather to seasonal scales. At this moment, a forecast system consisted of FV3, MOM6 and CICE5 has been coupled using the NEMS mediator. The WAVEWATCH III (WW3) is being added to the system and the land component will be upgraded to Noah-MP model. Besides existing data assimilation (DA) system for the atmosphere model, the DA systems for MOM6, CICE5, Noah-MP, GOCART (aerosol), and WW3 are being added to the coupled system. Once completed, the coupled system will be the next generation sub-seasonal to seasonal (S2S) forecast system based on the FV3 dynamical core at NCEP. During the initial development phase, the focus is on the sub-seasonal time scale (0 - 35 days forecast).

In this presentation, we will present the current design of the mediator. A 35-day control experiment using the coupled FV3-MOM6-CICE5 model is presented and compared with observations. Preliminary results show that the model has certain prediction skills for sub-seasonal variability in the equatorial regions. Several additional experiments are also performed to understand the strengths and weaknesses of different regridding methods used to interpolate coupling fields between two components. Finally, we will discuss the ongoing collaborative development effort to improve air-sea flux calculations using fractional land-sea mask and exchange grid.