The NUIST Earth System Model (NESM) version 3: description and preliminary evaluation

The Nanjing University of Information Science and Technology Earth System Model version 3 (NESM v3) has been developed, aiming to provide a numerical modeling platform for cross-disciplinary earth system studies, project future Earthu0027s climate and environment changes, as well conduct subseasonal-to-seasonal prediction. While the previous model version NESM v1 simulates well the internal modes of climate variability, it has no vegetation dynamics and suffers considerable radiative energy imbalance at the top of the atmosphere and surface, resulting in large biases in the global mean surface air temperature, which limit its utility to simulate past and project future climate changes. The NESM v3 upgraded the atmospheric and land surface model components and improved physical parameterization and conservation of coupling variables. Here we describe the new versionu0027s basic features and how the major improvements were made. We demonstrate the v3 modelu0027s fidelity and suitability to address the global climate variability and change issues. The 500-year PI experiment shows negligible trends in the net heat flux at the top of atmosphere and the Earth surface. Consistently, the simulated global mean surface air temperature, land surface temperature and sea surface temperature (SST) are all in a quasi-equilibrium state. The conservation of global water is demonstrated by the stable evolution of the global mean precipitation, sea surface salinity (SSS) and sea water salinity. The sea ice extents (SIEs), as a major indication of high latitude climate, also maintain a balanced state. The simulated spatial patterns of the mean outgoing longwave radiation, SST, precipitation, SSS fields are realistic, but the model suffers from a cold bias in the North Atlantic, a warm bias in the Southern Ocean and associated deficient Antarctic sea ice area, as well as a delicate sign of the double ITCZ syndrome. The estimate radiative forcing of quadrupling carbon dioxide is about 7.24 W m -2 , yielding a climate sensitivity feedback parameter of −0.98 W m -2  K -1 , and the equilibrium climate sensitivity is 3.69 K. The transient climate response from the 1 pct/year increasing CO 2 experiment is 2.16 K. The modelu0027s performance on internal modes and responses to external forcing during the historical period will be documented in an accompanying paper.