Dynamic downscaling of the twentieth-century reanalysis over the southeastern United States
A 108-year (1901–2008) downscaling of the twentieth-century reanalysis (20CR) using the Regional Spectral Model (RSM) has been conducted for the southeastern United States (SEUS) at a horizontal grid resolution of 10 km. This 108-year product, named as the Florida Climate Institute-Florida State University Land–Atmosphere Reanalysis for the southeastern United States at 10-km resolution version 1.0 [FLAReS1.0], has primarily been developed for anticipated application studies in hydrology, crop management, ecology, and other interdisciplinary fields in the SEUS. The analysis of this downscaled product reveals that it ameliorates the issue of artificial discontinuity in the precipitation time series of the 20CR from the variations inherent to RSM. This centennial scale product allows us to begin examining decadal scale variations of the regional features of the SEUS. The fidelity of the low-frequency variations of the winter rainfall associated with the Atlantic Multi-decadal Oscillation (AMO) and the Pacific Decadal Oscillation is reasonably well captured in FLAReS1.0. In fact, the modulation of the El Nino-Southern Oscillation (ENSO) teleconnection with the SEUS rainfall by AMO in the downscaled product is also validated with observations. The ENSO-associated variations of accumulated rainfall from landfalling hurricanes in the SEUS are also well simulated in the downscaled climate simulation. It is to be noted that the success of this dynamical downscaling is also because the global reanalysis of 20CR showed comparable fidelity in these low-frequency variations of the SEUS climate. This method of dynamic downscaling global reanalysis with inclusion of spectral nudging at large wavelengths (in this case ≥500 km) toward the driving global reanalysis (20CR) is sometimes referred as a form of regional reanalysis.