Regional Climate Modeling and Air-Sea Coupling

Abstract

Regional models were originally developed to serve weather forecasting and regional process studies. Typical simulations encompassed time periods on the order of days or weeks. Thereafter, regional models were also more frequently used as regional climate models for longer integrations and climate change downscaling. Regional climate modelling or regional dynamic downscaling, terms that are used interchangeably, developed as a branch in climate research at the end of the 1990s, out of the need to bridge the obvious inconsistencies at the interface of global climate research and climate impact research. The primary aim of regional downscaling is to provide consistent regional climate change scenarios with relevant spatial resolution to serve detailed climate impact assessments. Similar to global climate modeling, the early attempts in regional climate modeling were based on uncoupled atmospheric models or stand-alone ocean models, an approach that is still maintained as the most common on the regional scale. However, this approach has some fundamental limitations, since regional air-sea interaction remains unresolved, and regional feedbacks are neglected. This becomes crucial when assessing climate change impacts in the coastal zone or the regional marine environment. To overcome these limitations, regional climate modeling is currently in a transition from uncoupled regional models to coupled atmosphere-ocean models, leading to fully integrated earth system models. Coupled ice-ocean-atmosphere models have been developed during the last decade and are currently robust and well established on the regional scale. Their added value has been demonstrated for regional climate modeling in marine regions, and the importance of regional air-sea interaction has become obvious. Coupled atmosphere-ice-ocean models and coupled physical-biogeochemical modeling approaches are increasingly used for the marine realm. The first attempts to couple these two approaches together with land surface models are under way. In addition, physical coupled atmosphere-ocean modelling is developing further, and the first model configurations resolving wave effects at the atmosphere-ocean interface are now available. These new developments now allow for improved regional assessment with broad consideration of local feedbacks and interactions between the regional atmosphere, cryosphere, hydrosphere, and biosphere.