Rationale

Recent climate modeling results have highlighted the Arctic as a region of particular importance and vulnerability to global climate change. Despite the climatic significance of the Arctic, many physical processes occurring in this region are still not well understood. Hence, it is not surprising that simulated climates of the Arctic vary widely, depending on the choice of climate model and physical parameterizations. A useful approach for understanding and modeling the arctic climate system is the development and application of regional climate models.

The rationale for constructing a high-resolution regional model of the arctic atmosphere is that the treatment of orography and the physical processes are limited in global climate models by both vertical and horizontal model resolution. Further, parameterizations of physical processes specific to the polar region can be tested and implemented in the regional model to assess their interaction with the regional climate system. A regional model of the arctic climate, when driven by analyzed lateral boundary conditions, has the additional advantage of minimizing the impact of model biases or errors from subpolar latitudes. This rationale has convinced several groups in the U.S., Canada, Germany, Denmark and Sweden (among others) to construct regional models of the arctic climate, ranging from atmosphere-only models with specified surface conditions to coupled system models including sea ice, ocean and land-surface submodels.

A powerful method for improving regional climate simulations is the comparison of simulations produced by different models with each other as well as with available observations. Strengths and weaknesses of model structures, numerics and parameterizations can be assessed side-by-side. The utility of model intercomparisons is greatly enhanced if the models operate under the same external constraints and use a data-rich case study such as SHEBA (Surface Heat Budget of the Arctic Ocean).

The purpose of the Arctic Regional Climate Model Intercomparison Project (ARCMIP) is to evaluate and improve regional climate models of the Arctic. Large errors are present in simulations of the arctic climate, both by regional and global models. Use of regional models (with specified horizontal boundary conditions) eliminates problems originating from lower latitudes that contaminate the solution in the Arctic. High-resolution regional models can be used investigate in detail arctic physical processes so that appropriate resolution and parameterization complexity can be determined. The need for regional climate model simulations is increasing in the context of local integrated assessment and socioeconomic applications.

The following broad questions have been identified for ARCMIP:

1. What processes are inadequately represented in Arctic simulations by regional models? What is the appropriate level of complexity of physical process parameterizations?
2. What is the level of uncertainty in current regional climate models of the Arctic, and how well can these models represent natural variability and anthropogenic change?
3. How can regional models best be employed for applications involving scenarios? (e.g. lateral forcing, multi-model ensembles)
4. What can be learned about the biases experienced in global climate model simulations of the Arctic by using Arctic regional climate models?