RESUME / ABSTRACT  


Assessment and correction of the surface 6-hly wind field of the NCEP/NCAR Reanalysis in the circum-polar Arctic


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David E. Atkinson


Geological Survey of Canada (Atlantic)
Bedford Institute of Oceanography






Abstract The NCEP/NCAR Reanalysis project is providing an important source of climate data for a wide variety of studies ranging over meteorological, climatological, and climate-dependent themes. The project combines observational data with an operational model to generate a variety of climatic parameters at multiple levels over lat/long or standard gaussian grids. In data sparse regions use of the model as an integrative basis forms an effective means to interpolate between and extrapolate into regions with little or no observational data. The contribution of observational data to the final result is thus, by definition, highly variable. Many applications for these data are at regional or local spatial scales, often below the effective resolution of the Reanalysis grid. The question of the accuracy with which the Reanalysis data reproduce observational records is thus of interest. This question is explored in this talk, focussing specifically on the wind field.

A direct comparison using vector and Pearson correlation statistics was conducted between in situ observational data and data from the nearest grid point in the 6-hly (10 m) wind field of the NCEP/NCAR Reanalysis set. This work was performed at a circum-polar scale, using 183 weather stations from throughout the circum-polar region: 50 stations from Russia, Norway, Greenland and Alaska, and 74 Canadian coastal and 59 Canadian interior sites from the Yukon, Nunavut and NWT. Other sources were also employed, including hourly data from Russian and American ice islands from the Arctic Ocean as well as southern Beaufort Sea oil platform data from ~1975 - ~1985. The comparisons were conducted over the 1950 - 2000 period, for various seasonal breakdowns (calendar seasons and open water/freeze up, as well as annual). Time series assessments, in which the correlation results for the entire circum-Arctic are averaged by year, were also performed, including comparison with indices of the Arctic Oscillation.

Results indicated good correlation for wind direction, improving at higher speeds, but systematic underestimation of wind speed, especially during high-magnitude events. Given that such events often engender some of the more dramatic responses in the natural environment, it was of specific interest to ensure they are adequately portrayed in the Reanalysis record. For this, correction algorithms were developed, trained against observational data, and applied. Results of the correction work were reasonably good, in that many events were identified and corrected, but some were missed because they have no discernible signature in the Reanalysis data. Time series results suggested a sensitivity of the model to decadal-scale variability associated with the Arctic Oscillation.