百余年来影响福建热带气旋的变化特征

应用1884—2003年影响福建的热带气旋资料, 采用突变分析、最大熵谱分析、连续小波变换以及正交小波变换等方法研究百余年来影响福建热带气旋频数变化的多时间尺度特征及其异常年份的海气背景场特征。结果表明:百余年来福建经历了3次少台期和2次多台期, 影响福建热带气旋频数具有准13年、准4年和准2.5年的振荡周期, 1971年为年频数变化的突变点; 影响福建热带气旋频数近百年呈弱的上升趋势, 但近十几年略微下降, 未来有偏多的趋势; 影响福建热带气旋异常偏多 (少) 的年份, 夏季500 hPa高度场上, 鄂霍次克海地区位势高度偏低 (高), 从高纬到低纬呈“-+-”(“ +-+”) 的距平型, 纬 (经) 向环流占优势, 西风带低槽偏北 (南), 副热带高压北界偏北 (南), 副热带高压脊线偏北 (南); 赤道中、东太平洋为明显的带状负 (正) SSTA距平区, 同时西太平洋热带气旋主要源区和西北太平洋上皆为正 (负) SSTA距平。由此可见, 影响福建热带气旋频数多寡与西太平洋热带气旋生成区的海温有关, 同时大气环流系统的位置和强弱对热带气旋路径的变化起着关键性作用, 从而使影响福建热带气旋频数的变化。

Variations in Activities of Fujian-affecting Tropical Cyclones During 1884-2003

Situated in the Southeast seaboard of China and facing the western North Pacific, Fujian Province is influenced by tropical cyclones (TC) as one of the major summer meteorological disasters at just a lower frequency than Guangdong, Hainan and Taiwan.The 1884—2003 tropical cyclone (TC) data affecting Fujian Province are utilized to investigate the variations of their activities in the Province by means of the trend analysis, mobile t-test, Cramer's scheme, maximum entropy spectrum technique, continuous and orthogonal wavelet transforms. On this basis, the atmospheric circulation and SST are examined in the year of TC anomaly influencing Fujian in an attempt to reveal the possible mechanisms for a scientific basis, with which to predict short-term climate.During the research period Fujian experiences three (two) stages of a lower (higher) number of typhoons hitting Fujian, with the turning points in 1902, 1931, 1955 and 1971 with the last being the year of abrupt change in the annual frequency. Affecting the frequency are the quasi-periodic oscillations at about 13, 4 and 2.5 years, particularly pronounced being the quasi-4 year mode.The annual TC frequency shows a weak rise during the 100 years on the whole but a slight drop in the past several decades. In terms of interdecadal variation, the frequency experiences the decrease-increase-decrease-increase-decrease phases, ushering in the increase in the next phase. From the interdecadal scale between the mid 1960s to the early 1990s, the time-dependent amplitude of the frequency is small compared to the anterior stage, meaning insignificant interannaul variation and low probability of TC anomaly years in this period.In the year of more (fewer) TC battering Fujian, the geopotential height on the summertime 500 hPa height field over the Okhotsk Sea is lower (higher), with the anomalies arranged as "-+-" ("+-+") from high to low latitudes, and zonal (meridional) circulations prevail, leading to the westerly trough northward (southward) of the mean, the northernmost limit and thus the ridge of the subtropical high northward (southward) of the mean and associated with this, a significant banded negative (positive) SSTA zone covers the middle-eastern Pacific at equatorial latitudes in contrast to a positive (negative) SSTA swathe that emerges in the dominant source of TC in the western Pacific and the northwestern Pacific. It follows that a higher or lower frequency of typhoons striking Fujian is related to SST at the source region for TC in the western Pacific and their tracks are strongly affected by the position and intensity of atmospheric circulation systems so that the Fujian-hitting typhoons'frequency changes accordingly.