Structure and Dynamics of the Quasi-Biennial Oscillation in Re-Analysis Systems

Abstract:

The tropical stratospheric Quasi-Biennial Oscillation (QBO) is an important source of interannual variability in the atmosphere. Because of its long period (~28 months), multi-decadal reanalyses are useful in providing a complete, global description of the QBO structure. We examine the QBO using 35 years (1980-2015) of meteorological fields, including ozone, produced by the new, ongoing, NASA MERRA-2 (Modern-Era Retrospective Analysis for Research and Application) reanalysis system, along with the original MERRA system. The assimilation of new data types (such as limb scanning observations, for example), in addition to the retuning of parameterized gravity wave drag (GWD) in MERRA-2 changes the momentum balance and mean circulations associated with the QBO. Results show that increasing tropical GWD forcing in MERRA-2 led to smaller zonal wind analysis increments associated with the QBO, while both MERRA-2 and MERRA have similar resolved wave QBO forcing in the lower stratosphere. The MERRA-2 dynamics generates a realistic, descending QBO associated mean meridional circulation. Ozone results show the largest amplitude ozone QBO signal near the ozone peak at 10 hPa with a secondary peak in the lower stratosphere. When limb scanning ozone observations become available (starting in 2004) in MERRA-2, the descending ozone QBO becomes better defined. While the MERRA-2 QBO is influenced by changes in the input observations over time, many dynamical structures and ozone features are shown to be consistent throughout the reanalysis period.