Relationship between equatorial pressure oscillations and tropical cyclones landing over China |
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| Authors: | Ji ZhongPing Xie JiongGuang Liang Jian Jin RongHua Wen Jing Weng XiangYu |
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| Institution: | 1. Guangzhou Central Weather Observatory, Guangzhou 510080, China
2. State Meteorological Center, Beijing 100081, China |
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| Abstract: | With daily reanalysis data by NCEP/NCAR and data of tropical cyclones landing over China from 1949 to 2005, the variation
of low-frequency oscillations of equatorial pressure and their relationship with tropical cyclones landing over China in the
summer half of the years (June through October) are studied for the 57 years, using spectral analysis and correlation analysis.
The results show that the summertime equatorial pressure is mainly of periodic oscillations of 5–7 days and 10–30 days and
the interannual variation of the intensity of its quasi-biweekly oscillation is significantly positive correlation with the
number of tropical cyclones landing over China. The quasi-biweekly oscillation is filtered from daily equatorial pressure
in May–November over the 57 years with inverse wavelet transform and the probability for tropical cyclones landing on coastal
China within four days before and after the oscillatory valleys of quasi-biweekly pressure at the equator is 59.7% and 73.0%
for June to October and July to September respectively. The model of atmospheric circulation for quasi-biweekly oscillatory
valleys of equatorial pressure in association with or without tropical cyclones landing over China in July–September is set
up with the composite analysis method. When the valleys are associated with (without) landfall, zonal (meridional) circulation
prevails in the mid and high latitudes of the Eastern Hemisphere, the high pressure ridge is weak (strong) near the Sea of
Okhotsk, the westerly zone is northward (southward), the subtropical high is westward (eastward) in location and strong (weak)
in intensity, the cross-equatorial flow is strong (weak) in southeast Asia, Southwest Monsoon is strong (weak) and stronger
(weaker) while in the valleys of pressure, being favorable (unfavorable) for tropical cyclones landing over China. The atmospheric
circulation model for oscillatory valleys of biweekly equatorial pressure in association with (without) tropical cyclones
landing over China, which can reflect the difference of atmospheric circulation between them, is beneficial to medium-term
forecasts of tropical cyclones landing over China.
Supported by An Open Project for the Laboratory of Forecast Systems at the State Meteorological Center |
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| Keywords: | equatorial pressure quasi-biweekly oscillatory valleys landfall tropical cyclones China atmospheric circulation models |
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