Why use Regional Climate Models?

Regional Climate Models

Regional climate models are used for understanding physical and dynamical processes underpinning climatic conditions at regional scales. These models are based on fundamental laws of physics and as such have applicability to all regions of the Earth. Some physical and dynamical processes essential to accurate simulation of weather and climate occur at scales too small to be resolved by regional models or too complex to be rendered into forms for exact numerical computation. These processes are represented by parameterizations that approximate the underlying physical behavior.

Regional climate models cover domains typically on the size of continents or large fractions of continents. Figure 1 shows the horizontal domain of a regional model for the US. Such models typically have horizontal resolution of about 50 km and have 15-30 levels in the vertical. Because they employ sub-global domains, regional models can be used to control "contaminating" influences of distant processes while focusing attention on the regional process of interest. Higher resolution of regional models reduces the span of grid cell averaging, therby highlighting the role of fine-scale features (e.g. fronts, low-level jets, mesoscale convective complexes).

Development of Regional Climate Models for Different Regions

Since regional climate models are based on fundamental laws of physics they should be applicable anywhere on Earth. However, the importance of physical processes represented by use of parameterizations may differ from region to region. For example, a simulation for the tropics would not require fine detail about physical processes in frozen soils, whereas an Artic simulation might not be as dependent on a wide range of vegetation classes or soil conditions.

Development of regional climate models for different regions by national laboratories and other research groups has tended to focus on accurate simulation for the range of climatic processes indigenous to that particular region, with less attention to processes not playing a dominant role.

Transferring Regional Climate Models to Other Regions

A question then arises about accuracy when a model used for a particular region is transferred to a domain that may include climatic processes not indigenous to its domain of development. Transferability experiments seek answers to questions about the generality of regional climate models to simulate different climatic regimes.

Recovering Generality

By applying ensembles of models (each unchanged for the duration of the experiment) to multiple domains, each representing a different climate regime (e.g., tropical vs. arctic) or one of multiple representations of a common climate regime (e.g., monsoons on different continents), transferability experiments expose opportunities for recovering generality that may have been lost or overlooked in the parameterization process.

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