Arctic System Reanalysis

The Arctic System Reanalysis (ASR) includes atmospheric, sea ice and land surface representations. Through data assimilation a broad-based set of historical data streams from the surface and space are combined. The domain of the ASR includes all of the northward flowing rivers that empty into the Arctic Ocean. The ASR is based upon: the polar-optimized version of the Weather Research and Forecasting model (Polar WRF), WRF variational data assimilation (WRF-Var) and High Resolution Land Data Assimilation System (HRLDAS). Polar WRF includes an improved Noah land surface model and specifications for the following sea ice attributes: extent, concentration, thickness, albedo and snow cover. WRF-Var assimilates NCEP-PREPBUFR observation data (in-situ surface and upper air data, remotely sensed retrievals and satellite radiance data). HRLDAS assimilates snow cover and depth, observed vegetation fraction and albedo. The T255 (0.7 degrees) horizontal resolution ERA-Interim reanalysis surface and upper air model level data are used to provide the background initial and lateral boundary conditions for the ASR.

ASR data assimilations with reduced resolution (30 km) have been performed and are known as ASR-Interim. The ASR-Interim version 1 (covering January 1, 2000 - December 31, 2010) is available from NCAR CISL RDA ds631.0. ASR-Interim version 2 (covering January 1, 2000 - December 31, 2011) with significant improvements has been completed.

The annual total accumulated precipitation from the ASR-Interim version 2 and from ERA-Interim are very similar. The added benefit of higher resolution with the ASR data assimilation (30 km for ASR versus ~80 km for ERA-Interim) can be seen along the mountainous west coast of North America, southeast Greenland, southeast Iceland, and western Scandinavia where more detailed and realistic features are evident in ASR. The results of the ASR-Interim version 2 are compared with 3-h surface observations from across the ASR domain. These comparisons are based on observations from more than 5,000 surface stations obtained from the National Climatic Data Center. Comparisons of results from ERA-Interim with the 3-h surface observations are also made. The much higher skill in resolving surface pressure, 2-m temperature, 2-m dew point temperature and 10-m wind speed are seen for both ASR analysis and forecast. ASR has much better performance than ERA-Interim.

Based upon the very encouraging ASR-Interim version 2 results, the ASR team is performing the final version with two nested domains at 15 km resolution for 2000-2012 (and at 10 km resolution for 2010-2012) and will be finished by May 2013.