Arctic temperature and precipitation as represented by reanalyses, compared with station data

While the observed sharp decline in end-of-summer sea ice extent is in part a response to Arctic warming, it also contributes to the warming in autumn and winter. This is because extra heat gained by the open ocean waters in summer is released back to the atmosphere once the midnight sun sets. Ice loss can also influence precipitation; while extensive open water represents a moisture source, a changing sea ice distribution can affect horizontal temperature gradients, and hence storm formation and tracks. As part of assessing such links, , we present results from a statistical comparison of Arctic temperature (2-meter temperature) and precipitation from three modern atmospheric reanalyses, MERRA, CFSR and ERA-Interim, with station data (over 700 sites) from the Global Historical Climatology Network (GHCN). We focus on the period from 1979-2010. Results show MERRA to correlate best with GHCN station data for precipitation; however, there are similar seasonal patterns of correlation seen when comparing the ERA-Interim and CFSR with GHCN data. Our use of atmospheric reanalyses recognizes that Arctic precipitation is very difficult to assess from surface observations alone. The station network is sparse, gauge measurements are prone to large biases, and there is no systemic measurement program over the central Arctic Ocean. As an extension to this study, the MERRA-Land data product, which includes two key differences from MERRA, will also be examined. MERRA-Land uses an updated version of the land catchment model used in MERRA while also incorporating gauge-based measurements. Since the initial results show that MERRA performs quite well compared the ERA-Interim and CFSR, it is of interest to compare precipitation fields for both MERRA and MERRA-Land across the Arctic. Each of these reanalyses capture major known features of Arctic precipitation, including: 1) peak annual totals over the Atlantic side of the Arctic linked to the Icelandic Low and the North Atlantic storm track, 2) low annual totals over the Canadian Arctic Archipelago, eastern Siberia and the central Arctic Ocean, 3) contrasting seasonal cycles over land (summer maximum, winter minimum) and the Atlantic sector (winter maximum, summer minimum). Reanalyses outputs are in agreement regarding an overall warming trend, especially over the eastern Arctic Ocean. Each of the reanalyses also indicates similar seasonal patterns across the Arctic (defined here as areas north of 60N), with an overall positive trend in wintertime precipitation across terrestrial Arctic areas. The largest discrepancy occurs over the north Atlantic sector, where ERA-Interim shows a drying trend while MERRA and CFSR indicate increased precipitation for all seasons.