Simulating the impact of the large-scale circulation on the 2-m temperature and precipitation climatology

• Published in: Climate dynamics Vol. 40; no. 7-8; pp. 1903 - 1920
• Main Authors: Bowden, Jared H., Nolte, Christopher G., Otte, Tanya L.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-04-2013; Springer; Springer Nature B.V
• Subjects: Air quality; Atmospheric circulation; Atmospheric temperature; Circulation; Climate change; Climate models; Climate science; Climatology; Climatology. Bioclimatology. Climate change; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Environmental aspects; Exact sciences and technology; External geophysics; Geophysics. Techniques, methods, instrumentation and models; Geophysics/Geodesy; Global climate; Meteorology; Oceanography; Precipitation; Precipitation (Meteorology); Simulation; Temperature; United States; ANW, Atlantic, Bermuda; USA; Regional climate modeling; Analysis nudging; Interior grid nudging; Spectral nudging; Bermuda high; Initialization; Climatology; Error estimation; atmospheric precipitation; Scale reduction; Nudging; Regional scope; Climate models; North America; Dynamic method; Atmospheric temperature; atmospheric circulation; Data assimilation
• ISSN: 0930-7575; 1432-0894
• DOI: 10.1007/s00382-012-1440-y

The impact of the simulated large-scale atmospheric circulation on the regional climate is examined using the Weather Research and Forecasting (WRF) model as a regional climate model. The purpose is to understand the potential need for interior grid nudging for dynamical downscaling of global climate model (GCM) output for air quality applications under a changing climate. In this study we downscale the NCEP-Department of Energy Atmospheric Model Intercomparison Project (AMIP-II) Reanalysis using three continuous 20-year WRF simulations: one simulation without interior grid nudging and two using different interior grid nudging methods. The biases in 2-m temperature and precipitation for the simulation without interior grid nudging are unreasonably large with respect to the North American Regional Reanalysis (NARR) over the eastern half of the contiguous United States (CONUS) during the summer when air quality concerns are most relevant. This study examines how these differences arise from errors in predicting the large-scale atmospheric circulation. It is demonstrated that the Bermuda high, which strongly influences the regional climate for much of the eastern half of the CONUS during the summer, is poorly simulated without interior grid nudging. In particular, two summers when the Bermuda high was west (1993) and east (2003) of its climatological position are chosen to illustrate problems in the large-scale atmospheric circulation anomalies. For both summers, WRF without interior grid nudging fails to simulate the placement of the upper-level anticyclonic (1993) and cyclonic (2003) circulation anomalies. The displacement of the large-scale circulation impacts the lower atmosphere moisture transport and precipitable water, affecting the convective environment and precipitation. Using interior grid nudging improves the large-scale circulation aloft and moisture transport/precipitable water anomalies, thereby improving the simulated 2-m temperature and precipitation. The results demonstrate that constraining the RCM to the large-scale features in the driving fields improves the overall accuracy of the simulated regional climate, and suggest that in the absence of such a constraint, the RCM will likely misrepresent important large-scale shifts in the atmospheric circulation under a future climate.