Anomalous Tropical Cyclone Activity in the Western North Pacific in August 2014
Anomalous Tropical Cyclone Activity in the Western North Pacific in August 2014
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DOI：
10.1175/bams-d-15-00125.1
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发表时间：
2015-12
影响因子：
8
通讯作者：
Lei Yang;Xin Wang;Ke Huang;Dongxiao Wang
中科院分区：
文献类型：
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作者：
Lei Yang;Xin Wang;Ke Huang;Dongxiao Wang
介绍。2014年北方夏季，北太平洋西部（WNP; 0-25 N, 105 E-180）经历了高度异常的热带气旋（TC）活动：8月初至9月初没有形成TC，而在气候学上出现了最大的TC形成（图24.1 a, b）。7月形成的5个台风中，有3个成为超级台风，使2014年成为1949年以来超级台风比例最高的一年（补充图S24）。1）. 热带气旋是西太平洋及其周边地区夏季降水的重要来源。这种8月份的低TC活动直接导致了南亚和整个WNP的异常低降水（Lin et al. 2015; supplementary Fig. S24）。2）. 7月份的三次超级台风共造成至少210人死亡，住房、电力和农业基础设施遭到严重破坏，总价值达73亿美元。（国际灾害数据库，www）emdat。/数据库)。这里使用的TC数据来自联合台风预警中心（JTWC）制作的最佳轨迹数据集，该数据集有1949年至2014年的TC记录。在本研究中，TC被定义为具有封闭的气旋环流和持续风速为25节（kt; 1 kt= 0.51 ms−1）或以上的风暴。最大风力超过135节的台风被称为超级台风。TC成因的变化与WNP的季节内振荡（ISO）密切相关（例如，Gray 1979; Camargo et al. 2009; Li et al. 2012; Li and Zhou 2013）。大约70%的WNP形式的tc出现在6月至12月的ISO活动期（Huang et al. 2011）。我们的研究还关注自20世纪70年代末以来一直在减弱的东亚夏季风（EASM）环流（Zhou et al. 2009），以及太平洋年代际振荡（PDO），它在2014年转为正值，并在2015年7月保持显著正值（补充图S24）。3）. 在2014年超强台风时间聚集后的长时间内没有TC发生的背景下，特别是在PDO可能由负向正转变和东亚地区多年代际变弱的背景下，研究了气候变化的相关机制和作用。历史背景。利用美国国家环境预报中心（NCEP）的再分析数据（Kalnay et al. 1996），分析了2014年8月的大气环流异常，包括850 hPa风、中层湿度（600 hPa）、低层相对涡度（850 hPa）、水平风的垂直风切变（200-850 hPa）、水分通量（850 hPa）和速度势（250 hPa）。与ISO相关的对流是基于美国国家海洋和大气管理局（NOAA）的内插输出长波辐射（OLR），其中包括1979年至2014年2.5× 2.5网格上的每日数据（Liebmann和Smith 1996）。研究中使用的所有异常都与1970-2010年的基期相关。
Introduction. During the boreal summer of 2014, the western North Pacific (WNP; 0–25 N, 105 E–180) experienced highly anomalous tropical cyclone (TC) activity: no TC formed from early August through early September, when maximum TC genesis occurs climatologically (Figs. 24.1 a, b). Of the five TCs that developed during July, three became super typhoons, making 2014 the year with the highest percentage of super typhoons since 1949 (Supplemental Fig. S24. 1). Tropical cyclones are significant sources of summer rainfall in the WNP and its surrounding regions. Such low TC activity in August has directly contributed to the anomalous low precipitation in south Asia and the entire WNP (Lin et al. 2015; Supplemental Fig. S24. 2). The three super typhoons in July together caused at least 210 deaths, and severe damage to housing and electrical and agricultural infrastructure, amounting to a total of 7.3 billion US dollars (International Disaster Database, www. emdat. be/database). The TC data used here are from the best-track dataset produced by the Joint Typhoon Warning Center (JTWC), which has TC records from 1949 through 2014. In this study, a TC is defined as a storm with enclosed cyclonic circulation and sustained winds of 25 knots (kt; 1 kt= 0.51 ms− 1) or above. A TC with maximum wind greater than 135 kt is considered a super typhoon. The variation of TC genesis is closely related to the intraseasonal oscillation (ISO) over the WNP (eg, Gray 1979; Camargo et al. 2009; Li et al. 2012; Li and Zhou 2013). Around 70% of the TCs in the WNP form during the active ISO period of June to December (Huang et al. 2011). Also of interest for our study are the East Asian summer monsoon (EASM) circulation which has been weakening since the end of 1970s (Zhou et al. 2009), and the Pacific decadal oscillation (PDO) which became positive in 2014 and has remained significantly positive through July 2015 (Supplemental Fig. S24. 3). We examine the relevant mechanisms, and role of climate change, in the long period with no TC occurrence after the temporal clustering of super typhoons in the WNP in 2014, especially in the context of a possible PDO phase transition from negative to positive and multidecadal weakening of the EASM.Historical context. Using the US National Centers for Environmental Prediction (NCEP) reanalysis dataset (Kalnay et al. 1996), we analyze the atmospheric circulation anomaly in August 2014, including 850-hPa wind, midlevel humidity (600 hPa), low-level relative vorticity (850 hPa), vertical wind shear of horizontal wind (200–850 hPa), moisture flux (850 hPa), and velocity potential (250 hPa). Convection associated with the ISO is based on the interpolated outgoing longwave radiation (OLR) from National Oceanic and Atmospheric Administration (NOAA), which comprise daily data on a 2.5× 2.5 grid from 1979 to 2014 (Liebmann and Smith 1996). All anomalies used in the study are relevant to the base period of 1970–2010.