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.