The Program for Climate Model Diagnosis and Intercomparison Diagnostic System: Implementing a New Strategy Beyond the Atmospheric Model Intercomparison Project (AMIP)

The Program for Climate Model Diagnosis and Intercomparison (PCMDI) was established in 1989 at the Lawrence Livermore National Laboratory (LLNL) with the principal mission to develop improved methods and tools for the diagnosis, validation and intercomparison of global climate models. The goal of the process is to eventually improve simulation of the regional climate effects of increasing greenhouse gases. In addition to comparing models, PCMDI continues to develop a modeling infrastructure by creating diagnostics that will be shared throughout the research community. PCMDI's early model intercomparison strategy was to solicit a few models that could be run for a specified period with prescribed sea-surface temperatures after being imported and adapted to the LLNL unclassified computer systems. Because of the enormous time required to prepare each model, the experiment was reversed and the modeling groups were asked to perform the controlled simulations themselves. In order to reach out to the entire atmospheric modeling community, the Working Group for Numerical Experimentation (WGNE) became the parent organization and the project was named the Atmospheric Model Intercomparison Project (AMIP). Eventually, more than thirty atmospheric modeling groups joined the effort to compare their model output (Gates et al. 1999). The general results showed that the models vary widely for some variables and are tightly clustered for other variables. Fig. 1 characterizes the wide array of results obtained in AMIP and underscores the need to better understand differences among models and between models and observations. As a result of AMIP, model development and improvement strategy has incurred a permanent change. Modeling groups routinely perform AMIP-like simulations as they improve their models and create new versions containing substantial modifications to parameterizations. Other model intercomparison projects (MIPs) have since sprung up, most notably, the Coupled Model Intercomparison Project (CMIP) and the Paleoclimate Model Intercomparison project (PMIP). AMIP itself has undergone substantial changes as we realized that the type and amount of data saved was inadequate. AMIP II was initiated to provide the community with a more comprehensive data set, a longer simulation period, and most important, a chance to evaluate more current models. For the most part the AMIP II simulation have been completed and the data are in the process of being prepared for distribution to research subprojects