VERY LOW FREQUENCY OSCILLATIONS IN THE VARIATIONS OF TROPOSPHERIC ATMOSPHERIC GENERAL CIRCULATION

Based on the monthly mean 500hPa maps over the Northern Hemisphere for 42 years(1951-1992),zonal harmonic analysis at 35°N and 55°N were carried out and westerly intensities between 35-55°N were calculated.Meanwhile,wavelet transform of percentage departures of westerlies and relative amplitudes of ultra-long wave were analyzed.Then,three kind of very low frequency oscillations were identified in the variations of tropospheric general circulation.1.Interdecadal oscillation;2.Interannaual oscillation (QBO)and 3.One-year oscnlation. Interdecadal oscillation maybe exists in wave-1 with 30-40 year oscillation and wave-3 with 20-year oscillation at 350N.QBO with 2.5-2.6 year oscillation were showed in westerlies as well as wave-2 and wave-3 at 550N.but no any direct relationship with stratopheric QBO(2.2 year) was found out.Maybe,the QBO in middle troposphere is caused by the interactions between the atmosphere and ocean or between the atmosphere and land surface.It may belong to auto-oscillation of the climate system.After wavelet transform,the one-year oscillation in some ultra-long waves and westerlies were more outstanding.It reflects a kind of rhythm in atmosphere.such as,arm-winter and cool-summer and vice versa.It is also an adjustment inner the climate system,which closely relates to the seasonal course of the general circulation.