Climate dynamics

Abstract:

The impact of solar irradiance changes on the winter polar stratosphere is investigated using a general circulation model in which the equatorial Quasi-Biennial Oscillation (QBO) is internally generated and self-sustaining. The model results compare favorably with observations, supporting previous findings that the equatorial zonal wind modulates the polar stratospheric response to solar irradiance changes. In the QBO easterly phase, Northern Hemisphere sudden stratospheric warmings are found to be more prevalent under solar minimum conditions than under solar maximum conditions. However, in the QBO westerly phase the reverse is true. The possible solar-modulation of the QBO period is also investigated. Although small changes are evident in the same sense as those observed, i.e. a lengthening of the period during solar minimum conditions, longer simulations would be required to verify the statistical significance of this result. Copyright 2005 by the American Geophysical Union.

Abstract:

ECMWF ERA-40 reanalysis zonal winds are very close to tropical rocketsonde and rawinsonde (radiosonde & radar wind soundings) observations up to 10 hPa. Above 10 hPa differences increase, although the ERA-40 data provide a good representation of tropical winds up to 2-3 hPa. The amplitudes of the quasi-biennial oscillation (QBO) and the semi-annual oscillation (SAO) derived from ERA-40 data match the rawinsonde and rocketsonde observations up to 2-3 hPa. We conclude that zonal-mean ERA-40 equatorial winds could be used, for most purposes, in place of rawinsonde station observations. Copyright 2005 by the American Geophysical Union.