西北太平洋热带气旋频数和强度变化趋势初探
Climatological Characteristics of Tropical Cyclones in the Northwestern Pacific
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摘要: 利用1951—2006年西北太平洋 (含南海) 热带气旋资料, 研究了不同强度热带气旋的气候变化特征。结果表明:超强台风 (近中心最大风速≥58m/s, 简称超强台风Ⅱ) 频数、强度和初、终旋日期的变化特征都不同于其他级别热带气旋; 西北太平洋热带气旋的总频数有长期减少趋势, 主要由热带低压和超强台风Ⅱ的长期减少趋势引起; 随着热带气旋强度增强, 出现月最大频数的月份逐渐推迟; 超强台风月频数最大值发生在秋季; 超强台风Ⅱ频数的年变化与除了超强台风Ⅰ(近中心最大风速为51~58m/s) 外的其他级别热带气旋反相关; 受超强台风Ⅱ减少影响, 热带气旋年平均最大风速有减小的长期趋势; 热带气旋的初、终旋日期没有显著的长期变化趋势, 但超强台风Ⅱ的初旋日期有推迟趋势, 终旋日期有提前趋势, 发生时间缩短。Abstract: Climatological characteristics of tropical cyclones in the Northwestern Pacific during 1951—2006 areinvestigated based on the tropical cyclone best track data from China Meteorological Administration.Tropical cyclones are classified into 6 different categories to study the long-term variation under the global warming background.From 1951 to 2006, nearly 33.9 tropical cyclones occur in the Northwestern Pacific every year.Tropical depressions contribute 18.8% and super typhoons contribute 17.8%.The total frequency of tropical cyclones in the Northwestern Pacific decreases since 1950s and the decreasing trend is1.8 times every 10 years.Frequency of tropical cyclones is highest in 1967 and lo west in 1998.The decrease trend of tropical cyclones frequency is mainly caused by tropical depression and super typhoon Ⅱ(maximum wind≥58 m · s -1, super typhoon Ⅱ for simple).The decrease trend of super typhoon Ⅱ ismost remarkable.Contributions of tropical depression and super typhoon Ⅱ frequencies decrease whilecontributions of other categories increase.Characteristics of frequency, intensity, the first and last date of super typhoon Ⅱ are different fromthose of other categories.About 56.3%of tropical cyclones in the Northwestern Pacific appear in summerseason, especially in August.The average monthly frequency is 7.9 in August and 0.3 in February.Withthe growing intensity of tropical cyclone, the maximum frequency postulate from August to October.Themaxim um frequency of super typhoon appears in autumn while those of other categories appear in August.Monthly frequencies of tropical depression and super typhoon Ⅱ take on decrease trends in autumn whilethose of other categories don' t show remarkable trends.The annual variations of super typhoon Ⅱ arenegative related with the annual variations of other categories except super typhoon Ⅰ.Yearly mean maxim um speed and minimum depression of tropical cyclones show a decrease trend.Yearly maximum speed oftropical cyclones decreases about 6.5 m · s -1 every 10 years, while yearly minimum depression has increased especially since 1987.Decrease trend of maximum speed is mainly caused by the decrease frequencyof super typhoon Ⅱ.The average first date of tropical cyclones is around 20 February and the average lastdate of tropical cyclones is around 15 December.The first date of tropical cyclones shows a slight delayingtrend.The first date of super typhoon Ⅱ have remarkable long-term delaying trend of 25 day s every 10y ears while the last date displays long-term advancing trend of 9 day s every 10 years.The last date of tropical storm has delaying trend while that of super typhoon Ⅰ has advancing trend.
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图 6 1951—2006年不同级别热带气旋的初、终旋日期的变化 (虚线代表初旋日期, 实线代表终旋日期)
(a) 热带气旋, (b) 热带低压, (c) 热带风暴—超强台风Ⅰ, (d) 超强台风Ⅱ
Fig. 6 Variations of the first and last date of different tropical cyclone during 1951 — 2006 (dashed line denotes the first date and solid line denotes the last date)
(a) tropical cyclone, (b) tropical depression, (c) tropical storm—super typhoonⅠ, (d) super typhoon Ⅱ
表 1 不同等级热带气旋月频数变化趋势 (单位: 1/10a)
Table 1 Long-time trends of monthly frequencies of tropical cyclones about different categories (unit : 1/10a)
表 2 不同等级热带气旋频数的相关系数
Table 2 Correlations among frequencies of tropical cyclones about different categories
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