The stratospheric QBO, the NCEP reanalysis, and RWB in the middleworld

The stratospheric quasi-biennial oscillation (QBO) has an irregular period that is unrelated to either the annual cycle or the intrinsic periods of the atmospheric waves that drive it. The QBO regulates mass flow across the tropopause and is a key component of the climate dynamical system.; The nature of the QBO is examined in Chapters 1 and 3 using 46 years (1958--2003) of reanalyses from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalyses (hereinafter "NCEP reanalyses"). Observations made by previous authors are verified, and new findings and methods are highlighted. A new QBO indexing method is presented in Chapter 2 and used throughout. A phase difference compositing technique provides "snapshots" of the QBO meridional-vertical structure as it descends, and "composite phases" provide a look at its time progression. The vertical-meridional distribution of the range in QBO zonal wind is compared with the annual cycle, and issues of phase asymmetries and phase locking with the annual cycle are critically examined.; Particular attention is focussed on the apparent "shift" that occurs in the NCEP reanalysis data around 1978, when satellite observations first became readily available. The effect of this shift on the time mean fields and the QBO are examined in detail in Chapter 4. Vertical temperature variations in the annual mean and QBO are underestimated by nadir-sounding satellites. A mechanism is suggested for how this may affect meridional circulations in data assimilation models. These results may assist in the construction of future data assimilation models and aid researchers in the interpretation of results based on NCEP reanalysis data.; Rossby wave breaking (RWB) near the tropopause facilitates the cross-tropopause exchange of ozone, aerosols, and other climatologically significant atmospheric constituents. The spatial and seasonal dependence of RWB near the subtropical tropopause between 330 and 360 K and the effect of the QBO on this process are examined in detail in Chapter 5. The method of identifying wave breaking events is described in detail in Chapter 2.