| Summary: | Since 1979, Atmospheric Motion Vectors (AMVs) from geostationary satellites have been used in the Japan Meteorological Agency (JMA) numerical weather prediction system. They provide valuable information of atmospheric motion from mid-latitudes to the tropics. However, there is little wind information at high-latitudes from the geostationary satellites and the radiosonde observations. The polar regions, therefore, have been remained as data poor regions for many years. Recently, polar winds have been derived on a quasi-operational basis at the Cooperative Institute for Meteorological Satellite Studies (CIMSS) of the University of Wisconsin-Madison by tracking structures in successive orbits from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites. The MODIS polar winds are promising data to improve the quality of analysis in the polar region and to bring better-forecast results. The MODIS polar winds assimilation experiments were performed for July 2003 and January 2004 using the JMA global three-dimensional variational data assimilation system (3D-VAR). Terra MODIS and Aqua MODIS polar winds in the Arctic were assimilated in the experiments. The experiments demonstrated positive impacts of the MODIS polar winds on short- and medium-range forecasts. Large improvements were found for the Northern Hemisphere in terms of geopotential height and wind fields. And improvements in typhoon track predictions were also found. Terra MODIS and Aqua MODIS polar winds in the Arctic have been operationally assimilated at JMA since 27 May 2004. In this paper, details of the results from the assimilation experiments are described. 1.
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