Publications

Stratospheric sudden warmings (SSWs) are a major source of variability during Northern Hemisphere Winter. The frequency of occurrence of SSWs is influenced by El Nino Southern Oscillation (ENSO), the Quasi-Biennial Oscillation (QBO), the 11-year solar cycle, and volcanic eruptions. This study investigates the role of ENSO and the QBO on the frequency of SSWs using NCAR's Whole Atmosphere Community Climate Model, version 3.5 (WACCM3.5). In addition to a control simulation, WACCM3.5 simulations with different combinations of natural variability factors such as the QBO and variable SSTs are performed to investigate the role of QBO and ENSO. Removing only one forcing, variable SSTs or QBO, yields a SSW frequency similar to that in the control experiment, however removing both forcings results in a significantly decreased SSW frequency. These results imply non-linear interactions between ENSO and QBO signals in the polar stratosphere during northern hemisphere winter. This study also suggests that ENSO and QBO force SSWs differently. The QBO forces SSW events that are very intense and whose impact on the stratospheric temperature can be seen between December and June, whereas ENSO forces less intense SSWs whose response is primarily confined to the months of January, February and March. The effects of SSWs on the stratospheric background climate is also addressed here.

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Richter, J. H.; Matthes, K.; Calvo, N.; Gray, L. J. (2011): Influence of the Quasi-Biennial oscillation and El Nino southern oscillation on the frequency of sudden stratospheric warmings. Journal of Geophysical Research, 116, D20111.