The New GFDL Global Atmosphere and Land Model AM2–LM2: Evaluation with Prescribed SST Simulations

TLDR

The study presents the configuration and performance of GFDL’s new global atmosphere–land model AM2–LM2, emphasizing its climatology and interannual variability related to ENSO. AM2–LM2 combines a new gridpoint dynamical core, prognostic cloud and aerosol schemes with a land model featuring soil and groundwater heat storage and stomatal resistance, and its performance is evaluated through prescribed SST simulations, including an AMIP II run and an ensemble of ten integrations with observed twentieth‑century SSTs. Compared with other AMIP II models, AM2–LM2 accurately reproduces circulation and precipitation patterns but suffers from cold surface and tropospheric biases, weak tropical cyclone and intraseasonal activity, while still realistically simulating ENSO‑related tropical precipitation and extratropical circulation anomalies.

Abstract

Abstract The configuration and performance of a new global atmosphere and land model for climate research developed at the Geophysical Fluid Dynamics Laboratory (GFDL) are presented. The atmosphere model, known as AM2, includes a new gridpoint dynamical core, a prognostic cloud scheme, and a multispecies aerosol climatology, as well as components from previous models used at GFDL. The land model, known as LM2, includes soil sensible and latent heat storage, groundwater storage, and stomatal resistance. The performance of the coupled model AM2–LM2 is evaluated with a series of prescribed sea surface temperature (SST) simulations. Particular focus is given to the model's climatology and the characteristics of interannual variability related to E1 Niño– Southern Oscillation (ENSO). One AM2–LM2 integration was performed according to the prescriptions of the second Atmospheric Model Intercomparison Project (AMIP II) and data were submitted to the Program for Climate Model Diagnosis and Intercomparison (PCMDI). Particular strengths of AM2–LM2, as judged by comparison to other models participating in AMIP II, include its circulation and distributions of precipitation. Prominent problems of AM2– LM2 include a cold bias to surface and tropospheric temperatures, weak tropical cyclone activity, and weak tropical intraseasonal activity associated with the Madden–Julian oscillation. An ensemble of 10 AM2–LM2 integrations with observed SSTs for the second half of the twentieth century permits a statistically reliable assessment of the model's response to ENSO. In general, AM2–LM2 produces a realistic simulation of the anomalies in tropical precipitation and extratropical circulation that are associated with ENSO.