A Statistical Analysis on the Effects of the Equatorial QBO on the Extratropical Stratosphere and Troposphere Based on Large Samples of Daily Data

The 46-year daily data of NCEP/NCAR Reanalysis are analyzed to investigate the effects of the equatorial quasi-biennial oscillation (QBO) on the large scale dynamics in the extratropical stratosphere and troposphere. Composites of the data in northern winter months with respect to the westerly or easterly phase of the QBO show that the stratospheric polar vortex is colder and stronger in the westerly phase in accord with previous studies. Statistical significance of the composite difference is tested by the large sample method with roughly 2000-day dataset for each phase of the QBO. Independence of serial daily data is taken account of by evaluating an effective time between independent samples. As a result, the most significant composite difference of the temperature is found near the tropopause in high latitudes, although the frequency distributions of the temperature for the two phases of the QBO overlap each other heavily.