Priority 4: Developing Community Models
Nested Regional Climate Modeling
Scale interactions, both spatial and temporal, are fundamental to atmospheric and oceanic prediction and have driven our approach to weather and climate forecasting. It has long been understood that improved prediction will attend the ability of global atmospheric models to capture the spectrum of scales, yet the use of nested climate models to address such interactions has until now been focused on downscaling (i.e., with regional model generally slaved to the global). This approach, however, misses the critical upscale interaction of mesoscale convection driving larger circulations. Related to this are two key shortcomings in current climate models: first, model parameterizations inadequately handle the mesoscale organization of convection, a missing link in scale interaction; and second, their triggering of convection tends to be premature and too frequent, leading to an overly-stable atmosphere, one less conducive to organized disturbances. NCAR scientists are addressing these issues through a new nested regional climate modeling effort.
A major component of NCAR's Prediction Across Scales program is the development of a nested regional climate model (NCRM). This supports the NCAR goal of improving understanding of the atmosphere, the Earth system, and the Sun. Within that goal, the effort serves the priorities of exploring atmospheric processes, improving prediction of weather and climate, and developing community models.
NRCM Development Goals:
- Seamlessly integrate the weather and climate models in NCAR to capture all important spatial and temporal scales;
- Support planned research and applications, addressing both scientific and societal issues; and,
- Provide a new community model akin to the Community Climate System Model (CCSM) and Weather Research and Forecasting Model (WRF).
With the NRCM, scientists hope to improve our understanding and simulation of complex, two-way scale interactions, with emphases on:
- Downscaling from global climate simulations (esp. in investigations of societal impacts);
- Upscaling from regional processes, including the effects of land and ocean processes; and,
- The impact of the mesoscale organization of moist convection on larger scales.
IIn FY2006, NCAR scientists conducted NRCM simulations with the Advanced Research WRF (ARW). These simulations have demonstrated a good reproduction of overall tropical climate by the ARW NRCM. The model can reproduce all main modes of tropical circulations at least as well as the NCEP/NCAR reanalysis, while doing an excellent job with tropical cyclones. The accompanying figure illustrates the fidelity of the NRCM's production of cyclones across the tropics.
Future plans include the continued analysis of the initial model output, embedding the ARW into the Community Atmosphere Model (CAM), and further climate experiments. This effort is being carried out under the sponsorship of NSF, USWRP, and the U.S.