The characteristics of the band‐pass filtered time series of the zonal averages of monthly mean values based on ERA‐40 reanalysis

By band‐passing the European Center reanalysis monthly mean values, we examined the frequency components of 2–3 years in height, latitude, and time domains. In the lower stratosphere, these frequencies have the typical shape of a stratospheric quasi‐biennial oscillation (QBO). We also found significant power of the same frequency components of specific humidity near the surface over the tropics, which can be regarded as an evidence of the effects of the QBO on the lower troposphere. Such variation of specific humidity might be caused by a change of the mid‐latitude branch of the Hadley circulation instead of direct control through the equatorial upper troposphere. Copyright © 2008 Royal Meteorological Society