中文摘要：

以中国气象局西北太平洋热带气旋资料为基础,分析1957—2004年影响我国并达到台风强度以上的三类热带气旋,即生成热带气旋、影响热带气旋和登陆热带气旋的频数和强度的变化。结果表明：强热带气旋频数在1957—2004年间呈显著减少趋势,强度越强,其减少趋势越明显。近50a台风以上强度的强热带气旋频次占总频次的比例没有明显的增加或减少趋势,强台风和超强台风比例呈减少趋势。1957—2004年热带气旋的最大强度呈线性减弱趋势,生成热带气旋和影响热带气旋的平均强度亦呈减弱趋势,登陆台风的平均强度也呈减弱趋势。

英文摘要：

Based on the tropical cyclone track dataset in the Northwestern Pacific from China Meteorological Administration, variations in frequencies and intensities of tropical cyclones （TCs） in the western North Pacific, affecting-China tropical cyclones （ACTCs） and landfall ones （LTCs） reaching typhoon intensity during 1957-2004 were studied. Frequencies of strong tropical cyclones showed significant decreasing trends from 1957 to 2004 and the linear trend was much larger when the intensity was strong. There were no increasing or decreasing trends in the ratios of strong tropical cyclones reaching typhoon intensity, while those reaching strong typhoon and super typhoon showed decreasing trends during 1957-2004. The maximum intensities ofTCs, ACTCs and LTCs had all decreased during the period of 1957-2004. The mean intensities of TCs and ACTCs illustrated decreasing trends and the mean intensity of LTCs achieving typhoon intensity also showed decreasing trends.