The Uncertainty of GFS over Eastern Asia: Error Analysis and Correction Using an Optical Flow Method

Base on the historical GFS prediction data over the Eastern Asia (60E-150E, 10S-70N) of January 2012,.the 500hPa geo-potential height prediction uncertainty of GFS is investigated through optical flow method. Taking the initial fields of GFS as real ones, the prediction errors of 24, 48 and 72h are analyzed and the 48h prediction is corrected using the 24h prediction and its optical flow error features. For the gradient of geo-potential height is small in tropical region, only the region north of 20N are analyzed. The result shows that the magnitude of optical flow between the prediction and the real field increases with forecasting hour, the maximal sample amount locates at 0.2 degree of 24h forecast and 0.4 of both 48h and 72h. The orient of optical flow concentrates to two peaks of 60-120 degree and 240-300 degree, the larger the forecast hour, the steeper of the peaks. The 48h correction result of optical flow is better than the GFS forecast on the mean forecast error, is slightly worse in mean absolute forecast error. (This research is supported by National Key R&D Program of China with Grand No. 2018YFC1507604).