Dynamical downscaling of regional climate for Alaska

Abstract:

The climate of Alaska is experiencing dramatic changes that have been enhanced by Arctic amplification. Understanding the mechanisms of change is necessary to better assess potential impacts. Due to sparse station observations in the vast state, dynamical downscaling of coarse resolution reanalysis/global climate model data using a regional climate model may be especially valuable to better understand the local climate. In this study we downscaled the ERA – Interim reanalysis data set 1979-2013 using the Weather Research and Forecasting (WRF) model to a 20km grid centered on Alaska. The results of the downscaling were compared to the original reanalysis to determine the value added by downscaling temperature and precipitation.

Owing to the complex topography of Alaska, the more realistic topography of WRF compared with the more smoothed topography of ERA – Interim allows for a better representation of the effect of terrain on the local climate. Preliminary results indicate warmer temperatures over higher elevations in winter relative to the reanalysis with cooler temperatures in summer. Lower elevations also tended to be cooler in winter in the downscaling. The downscaling tended to be wetter when compared to the original reanalysis. When compared locally with station data, the Fairbanks downscaling was warmer than observations while the Juneau downscaling, being in more complex terrain, tended to follow the station observations more closely than the reanalysis. This demonstrates that, with the added detail of topography and mesoscale processes, dynamical downscaling enhances the local information of temperature and precipitation in Alaska.