Arctic upper-level winds from reanalyses and TOVS satellite retrievals

Accurate upper-level wind fields over the Arctic are required for a variety of applications, including calculations of heat and moisture transport as well as analyses of circulation features. Reanalysis products from meteorological forecast centers perform well in areas where conventional data are dense, but studies have shown that their realism in data-sparse regions, such as the Arctic Ocean, is less certain. Upper-level winds from two reanalysis data sets, the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) and the ECMWF (European Center for Medium Range Weather Forecasting) Reanalyses are first evaluated. Independent rawinsonde data from two Arctic field programs that were not assimilated by the models are compared to reanalysis wind products for five thick layers between 1000 and 300 hPa. Both reanalyses exhibit large biases and are significantly too westerly and too northerly. Total wind speeds are too strong by 25 to 65% relative to rawinsonde values. Root-mean-square errors in u- and v-component winds are substantially larger than the mean values.

In an attempt to improve upon this situation, we calculate upper-level wind fields from satellite-derived temperature profiles using data from the TIROS Operational Vertical Sounder (TOVS) processed with the Improved Initialization Inversion algorithm combined with 10-m winds from the NCEP Reanalysis. The thermal-wind relationship, corrected with a new mass conservation techinique developed by Zou and Van Woert (2002), produces wind fields with no significant bias compared to rawinsonde measurements from SHEBA. Root mean square errors are approximately 5 m/s below 500 hPa.