西北太平洋热带气旋运动及其突变的若干统计特征

STATISTICAL CHARACTERISTICS OF TROPICAL CYCLONE MOTION AND SHARP TURNING OVER NORTH WESTERN PACIFIC

利用中国气象局上海台风研究所热带气旋（Tc）最佳路径资料，对1949-2010年共62年西北太平洋（包括南海）热带气旋的运动特征进行统计，包括TC路径折角和移速的时空分布，折角与移速、气压之间的关系以及我国近海和大陆TC异常路径的类型、地理分布等特征。最后就TC路径突变的折角标准及其发生概率进行了讨论。结果表明，（1）西北太平洋TC年平均移速略呈下降趋势，而平均折角年际变化在1980年代末之前呈上升趋势，之后呈下降趋势。（2）平均移速随纬度增高而增大，TC生成源地（菲律宾群岛以东和南海）为移速低值区；平均折角在日本岛以东洋面较小，南海、台湾岛附近较大。（3）西北太平洋TC12h平均折角为14．51°，左、右折频次分别占总数的44．57％和55．43％。两者在0—90。区间随角度增大偏折频次减少，而〉90°有所增多。（4）一般移动快的TC折角较小，而折角大的TC移动慢；较强TC折角小，而折角大的TC较弱。（5）TC在我国近海和大陆出现的突变路径主要包括西行北（南）折、北上东（西）折、打转和停滞等，其中西折出现频次最多。（6）TC折角〉45°的出现概率〈4．6％，〉30°的出现概率〈13．19％。若区分左、右折，则〉45°的概率都〈2．8％，〉30。的概率〈11％。TC路径的突然转折是小概率事件。

Abstract： Based on the best track data of tropical cyclones （TCs） from Shanghai Typhoon Institute, China Meteorological Administration, the characteristics of TCs （except tropical depressions） movement, including the spatial and temporal distribution of the turning angles and moving speed of TCs and the relationship between the turning angles and the moving speed and intensity, are statistically analyzed for the time 1949 to 2010 over the north Western Pacific ocean （including the South China Sea）. Then a statistical analysis is performed to study the TC abnormal motions over the offshore water and mainland of China. Finally, the standard of sharp turning angles and their probabilities are discussed. Results show that the interannual variability of generation of north Western Pacific TCs decreased meanwhile their average moving speed declined slightly. However, the turning angles ascended before the end of 1980s but declined after it. Average moving speed increases against latitude with the lowest-value area occurring over the ocean east to the Philippine Islands and the South China Sea. Average turning angle is small in the Sea of Japan but large in the South China Sea and Taiwan Island. The number of left-turning and right-turning in 12 hours is almost equal, taking up 44.57% and 55.43% respectively. The average angle is 14.51 ° in 12 hours. The number of turning angle decreases in the section from 0 ° to 90 °but increases slightly after 90°. Generally, fast-moving TCs have small angles while large-angle TCs move slowly. Strong TCs have small angles while large-angle TCs are weak. The abnormal TC tracks in the offshore and mainland of China mainly include westward-turning, northward turning, eastward turning and southward-turning, rotating, and stagnation. The probability of occurrence is less than 4.6% for a turning angle larger than 45 °, and less than 13.19% for one larger than 30 °, to appear. If the turning angle is grouped based on whether it is to the right or left, the probability of occurrence is less than 2.8% if the angle is larger than 45 ° and less than 11 % if it is larger than 30 °. The abrupt turning of TC moving direction is an event of small probability.