西北太平洋TC移动速度异常及预报误差特征的分析

利用国家气象局和上海台风研究所(CMA-STI)整编的西北太平洋1970—2009年热带气旋(TC,Tropical Cyclone)及TC最佳路径数据集和2005—2010年的TC路径预报误差资料,应用百分位法,确定TC移动速度异常指标,分析了40 a来西北太平洋TC移动速度及其变化异常发生的时空分布特征,研究了TC速度预报误差对路径预报误差的影响及其与大尺度引导气流之间的关系。结果显示:1)西北太平洋TC移速及移速变化累积概率达95%(5%)分位数的阈值分别为10.8 m·s~(-1)(1.43 m·s~(-1))和2.42m·s~(-1)(-1.72 m·s~(-1))。2)快速移动及加速的TC大都出现在日本海地区,而缓慢的和减速移动TC主要出现在南海区域。3)TC移动速度异常的季节变化表现为,快速移动的TC在5月出现的频率达到最高,缓慢移动的TC在10月频率达到最高,加速移动的TC在6月频率达到最高。4)近6 a的TC移速预报误差对TC路径预报误差的贡献平均约为41.6%。5)对TC路径预报误差偏大,且移速预报误差贡献大的个例分析显示,该个例大尺度环境引导气流偏弱使TC移动速度偏慢。而如果预报的大尺度环境引导气流偏强,使预报的TC移速偏快,那么就容易导致大的路径预报误差。

Analysis of tropical cyclone motion velocity anomalies over the western North Pacific and their forecast error

Tropical cyclones(TCs) cause substantial adverse impacts on economies and human life.Forecasting the landfall of TCs is an important part in the prediction of TC tracks.Previous studies have focused mainly on the moving paths of TCs,especially the moving direction before landfall.However,not only the location but the timing of landfall is crucial.A successful prediction emerges only if these two aspects are combined.After landing,slow-moving TCs induce large amounts of precipitation locally,causing serious problems to the people living in the area.This study focuses on the changes in TC moving speed in the TC tracks,and analyzes the moving speed of TCs along with their temporal and spatial distribution changes in the hope to help improve TC track predictions.The study is based on the TC best track dataset for the western North Pacific over the period 1970-2009 provided by the National Meteorological Bureau and Shanghai Typhoon Institute(CMA-STI),along with TC track prediction error data for 2005-2010,and applies a percentile method to determine the anomaly index of the TC moving speed.The characteristics of the temporal and spatial distributions of anomalous TC moving speed and its change during the last 40 years over the western North Pacific are analyzed.The effect of TC moving speed prediction error on track prediction error and the relationship between large-scale steering flow and the error for TC moving speed prediction are studied.The results show that:(1) The cumulative probability at the 95%(5%) quantile thresholds for TC moving speed and its variation of anomalies in the western North Pacific are 10.8 m·s^-1(1.43 m·s^-1) and 2.42 m·s^-1(-1.72 m·s^-1),respectively;(2) Fast-moving or accelerated-moving TCs mostly appear in the area of the Japan Sea,while slow-moving or decelerated-moving TCs occur mainly in the region of the South China Sea;(3) The seasonal variation of anomalous-moving TC represents that the frequency of fast-moving(slow-moving) TCs is highest in May(October) and that of accelerated-moving TCs tends to be highest in June;(4) In the last 6 years (2006-2011),the prediction error of TC moving speed contributes on average about 41.6% of TC track prediction error;(5)In the case study of a TC with large track prediction error that is deduced more by moving speed prediction error,the results show that the weak large-scale environmental steering flow makes the TC move slowly.If the forecasted large-scale environmental steering flow is strong,the predicted TC moving speed will be faster,which may lead to large track prediction error.