摘要
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.
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.
基金
An Open Project for the Laboratory of Forecast Systems at the State Meteorological Center
