STUDY ON THE RELATIONSHIP BETWEEN THE VOLUME OF TROPICAL CYCLONE AND ITS INTENSITY
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摘要: 热带气旋(TC)的结构(含形态)与强度及其变化关系密切，著名的Dvorak定强技术即为TC形态(水平)变化与强度关系的生动描述，近年来水平尺度与强度变化的关系也渐受关注。然而，至今未涉及整体形态(即体积)与TC强度变化的关系。利用欧洲中期数值预报中心(ECMWF)0.25 °的ERA-Interim再分析资料，统计并初步分析了2006—2015年西北太平洋TC的外围水平尺度和“体积”的特征及其与强度的可能关系：水平尺度与TC强度的相关性总体较弱；而TC“体积”与强度的相关性更显著，且TC“体积”随强度增强而增大的关系适用于所有强度级别；此外，TC垂直尺度(正涡度区伸展高度)与强度也有一定的正相关，且在TC较弱时(台风强度以下)更显著。伴随较弱TC增强的主要是垂直尺度的增大，当TC达到台风强度后，与TC强度继续增强相伴随的主要是水平尺度的增大。TC“体积”能较好地综合表征水平尺度和垂直尺度与TC强度变化的关系，借助TC“体积”对TC强度预报有一定的参考价值。Abstract: The tropical cyclone (TC) structure (including shape) is closely related to the TC intensity and intensity change. The famous Dvorak technique is just one of the techniques that describe the relationship between TC horizontal shape and intensity. Recently, the relationship between horizontal size and intensity has been paid more and more attention to. However, the overall shape (volume) of TC and its relationship with TC intensity has not been addressed so far. Based on the ERA-Interim reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) with a horizontal resolution of 0.25 degrees, the characteristics of the horizontal size (R) and "volume" of TC in the Northwest Pacific during 2006—2015 and their relationships with TC intensity were statistically analyzed. The results show that the correlation between the R and TC intensity is generally weak. While the correlation between TC "volume" and TC intensity is relatively significant, the "volume" increases with TC intensification, and this relationship applies to all intensity levels. In addition, the TC vertical size (extended height of positive vorticity) also has a significant correlation with TC intensity, which is more significant when TC is relatively weaker (below the level of typhoon). This suggests that the weak TC enhancement mainly accompanies with the increase in vertical size. When TC intensity reaches the level of typhoon, further intensification of TC mainly accompanies with increase in horizontal size. The TC "volume" can better characterize the correlation between horizontal size, vertical size and TC intensity. It has certain reference value for intensity forecast.
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Key words:
- Northwest Pacific /
- tropical cyclone /
- volume /
- horizontal size /
- intensity
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图 1 TC“体积”计算方法示意图
a. 0603号台风Ewiniar 2006年7月4号00 UTC四层TC相对涡度分布示意图；b. 975 hPa层上相对涡度分布(填色，单位：1×10-5 s-1)及平均半径(Ri)计算示意图。
图 2 1 000 hPa风场(绿色矢量)和相对涡度场(红色等值线，单位：1×10-5 s-1)与红外云图叠加情况
a. 0601号台风Chanchu 2006年5月11日00 UTC；b. 0603号台风Ewiniar 2006年7月4号00 UTC。
图 3 1 000 hPa层上相对涡度1×10-5 s-1等值线平均半径(R_1 000，单位：km)与JTWC最外围闭合等压线平均半径(ROCI，单位：km)的对比
a. 0601号台风Chanchu；b. 0603号台风Ewiniar。
图 4 TC不同强度等级下1 000 hPa层上水平尺度(R_1 000)变化(a)、TC平均强度随1 000 hPa层上水平尺度变化情况(b)
a中的垂直误差棒代表均值在0.05置信水平下的置信区间，横坐标上方数字代表该强度等级下的样本数，TS为热带风暴，STS为强热带风暴，TY为台风，STY为强台风，Super TY为超强台风；b中蓝灰色柱表示各水平尺度分组所占比例，红色点线表示分组平均强度。
图 6 a. 2006—2015年TC“体积”的区域分布，网格距为5 °×5 °，每个网格中的数字代表样本数，填色表示网格中的平均“体积”(样本数小于5个，缺乏代表性，不填色)；b. “体积”随纬度的变化；c. “体积”随经度的变化，其中虚线为平均“体积”。
图 9 2006—2015年TC不同强度等级下“体积”(a)，垂直伸展高度变化(b)
垂直误差棒代表均值在0.05置信水平下的置信区间，横坐标上方数字代表该强度等级下的样本数，TS为热带风暴，STS为强热带风暴，TY为台风，STY为强台风，SuperTY为超强台风。
图 10 2006—2015年TC“体积”(红色)、TC最高伸展高度上的气压(蓝色)以及TC强度(灰色)的生命期合成
横坐标上的时间0 h代表TC第一次达到最大强度，-120~0 h为达到最强之前，0~120 h为达到最强之后。纵坐标表示各时刻统计量与最强时刻的比值。
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