A STUDY ON THE CRITERION OF EXTRATROPICAL TRANSITION OF WESTERN NORTH PACIFIC TROPICAL CYCLONES
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摘要: 用体现热带气旋(TC)热力学特征的“相空间”(简称CPS)方法,加入了体现TC动力学特征的两个参数,即中低层风速切变参数和涡倾斜参数,对2000—2007年的222个TC进行检验。结果表明,CPS方法在增加了动力学参数后,可以更好地描述西北太平洋地区的TC变性过程,弥补了CPS方法对TC动力学特征描述的欠缺,同时客观判据的判断结果与《热带气旋年鉴》资料更相近。Abstract: A number of the tropical cyclones (TC) moving into the mid-latitude regions sometimes undergo a process of extra-tropical transition (ET). It can frequently produce intense precipitation and strong winds which can be a serious threat to land and maritime activities. As the phase space method considers mainly the thermodynamic characteristics but rarely the dynamic characteristics of TC, two more parameters are proposed here to improve the method of determining the extra-tropical transition. One is an inclined vortex parameter and the other is the vertical wind shear. More than 200 cases of TC are analyzed by using the two parameters to examine their reliability. According to the study above, an objective criterion of ET is developed for operational application. And there is also a general flow which can separate the TC and extra-tropical cyclones. And then a test based on the data from 2000 to 2007 is carried out. The results show that the objective criterion to distinguish TC from extra-tropical cyclones is much better than the phase space method only.
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Key words:
- ropical cyclone /
- extra-tropical transition /
- phase space /
- vortex-tilt /
- wind shear
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表 1 热带气旋与温带气旋差异
因子序号 热带气旋 温带气旋 1 暖心结构 冷心结构 2 正压结构 斜压结构 3 轴对称为主 非轴对称居多 4 最大风速在TC中心附 最大风速在对流层 近对流层低层及边界层 中高层的TC中心以外 表 2 CPS方法和“CPS+V”方法判断TC变性对比情况
TC 方法 ΔV=-1 ΔV=0 ΔV=1 变性 CPS方法 0.52 0.52 0.52 CPS+V方法 0.61 0.65 0.67 未变性 CPS方法 0.96 0.96 0.96 CPS+V方法 0.95 0.95 0.95 表 3 典型TC涡度中心偏离度 单位:°。
典型
TC第一象限
(Lon > 0,Lat > 0)第二象限
(Lon < 0,Lat > 0)第三象限
(Lon < 0,Lat < 0)第四象限
(Lon > 0,Lat < 0)径向 0.44 -0.47 -0.53 0.39 纬向 0.35 0.38 -0.45 -0.51 D 0.56 0.6 0.7 0.64 比例/% 7.7 9.5 19.7 16.2 表 4 变性TC涡度中心偏离度 单位:°。
典型TC 第一象限 第二象限 第三象限 第四象限 径向 0.60 -0.93 -1.07 0.71 纬向 0.82 0.91 -0.46 -0.41 D 1.02 1.30 1.17 0.82 比例/% 29.1 31.5 7.2 9.4 表 5 CPS方法和“CPS+D”方法判断TC变性对比情况
TC 方法 D=1 D=1.2 D=1.5 变性 CPS方法 0.52 0.52 0.52 CPS+D方法 0.65 0.61 0.58 未变性 CPS方法 0.96 0.96 0.96 CPS+D方法 0.96 0.96 0.96 表 6 基于每个TC的CPS和改进后的方法比较
方法 CPS方法 改进后的方法 年鉴中未变性TC样本数 157 157 空报比例/% 28.1 26.7 年鉴中变性TC样本数 65 65 漏报比例/% 18.5 9.2 表 7 基于每个时次的CPS和改进后的方法比较
方法 CPS方法 改进后的方法 非变性个例总数 6 044 6 044 空报比例/% 4.0 3.6 变性个例总数 274 274 漏报比例/% 48.2 35.0 表 8 客观方法漏判变性TC(仅列出有国际编号TC)带下划线台风编号为同时被JMA和CMA年鉴漏判或空判。
年份 与中国台风年鉴比较 与JMA年鉴比较 2000 001,010 001,003,009,010 2001 / 109,122 2002 222 215,222,225 2003 / 321 2004 413 428 2006 607 607 2007 704 707,719 表 9 同表 8,但为空判
年份 与中国台风年鉴比较 与JMA年鉴比较 2000 004,006,012,014,017,018,019,020 019 2001 101,115,121 2002 201,202,205,207,213,214,217,224,226 201,202,214 2003 301,302,304,310,312,314,315,317,319 302,312 2004 410,412,415,420,422 415,420 2005 501,520 520 2006 609,610,617,623 609,610,617,623 2007 723,724 723,724 -
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