Differences between the QBO in the first and in the second half of the ERA-40 reanalysis H. J. Punge1,2 and M. A. Giorgetta1 1Max Planck Institute for Meteorology, Bundesstr. 53, 20146 Hamburg, Germany 2IMPRS on Earth System Modelling, Bundesstr. 53, 20146 Hamburg, Germany
Abstract. The representation of the quasi-biennial oscillation (QBO) is investigated in the
ERA-40 reanalysis. In the lower stratosphere, where there are a reasonable number of
observations, the representation
of the QBO is equally good throughout the record.
However, strong differences between the first and the second half
of the zonal wind data set are found in the upper stratosphere, with a typical
offset of –10 m/s in the equatorial zonal wind in the earlier part versus the
later part of the ERA-40 record. At the same time, the strength of the QBO is similar.
The 7-year running means of zonal wind, wind shear and temperature
reveal interesting structures with major changes occuring in the beginning and the middle of the 1980s.
Possible explanations are discussed. The identified change of the
reanalysed wind profiles over
time in ERA-40 demands for a careful use of equatorial upper stratospheric winds
from the reanalysis e.g.~for model validation purposes.
Citation: Punge, H. J. and Giorgetta, M. A.: Differences between the QBO in the first and in the second half of the ERA-40 reanalysis, Atmos. Chem. Phys., 7, 599-608, doi:10.5194/acp-7-599-2007, 2007.