On Interdecadal Variations in Frequency of 1884~2003 Tropical Cyclones Influencing Fujian and Investigation of Causes of the Anomalies

The paper investigates the multiple time scale features of the annual frequency of tropical cyclones (TC) affecting Fujian and the air - sea background in abnormal TC frequency years in 1884~2003, leading to the conclusions as follows: (1) The province experiences two (three) stages of more (fewer) TC hitting, with the turning years being 1902,1931, 1955 and 1971, and the last in particular serves as the strong turning point for the frequency change on a yearly basis. The frequency experiences oscillations in quasi-13, -4 and -2.5 years, and especially the quasi-4 year oscillations are the most significant;(2) examining the summertime 500hPa height field in the years of more (fewer) TC striking the province, we find the geopotential heights over the Okhotsk Sea to be lower (higher) than in normal years, and the anomaly to be characterized by a "- + -" ("+ - +") pattern from high to lower latitudes, the zonal (meridional) circulations to prevail, the westerly trough, the northern limit of the subtropical high (sub-high) and its ridge line to be northward (southward) of average; (3) a noticeable negative (positive) SSTA band is found over the eastern equatorial Pacific as well as a swathed positive (negative) SSTA in the western Pacific dominant source region of TC and also the NW Pacific, indicating that the frequency of TC affecting Fujian depends not only on SST in the TC genesis area but the position and intensity of atmospheric circulations that play a crucial role in the TC track, which thus affects the yearly frequency of TC influencing Fujian.