Over the Xizang Plateau,the 500 hPa hight forecast error is almost nega-tive in every month of the year,with the largest negative value appeared insummer,but it approaches to zero in winter.

• 青藏高原上空500百帕预报全年基本上都是负偏差,以夏季负偏差最大,春秋季减小,冬季趋于0,各月之间有近于正弦波型式的年变化规律性。