The influence of the equatorial upper stratosphere on the frequency of sudden stratospheric warmings (Invited Speaker)

The frequency and timing of observed sudden stratospheric warmings is influenced by a number of different factors, which include natural internal variability, the QBO, ENSO and the 11-year solar cycle. An understanding of the mechanism of these influences is important in investigations of future climate change in the stratosphere and its impact on the weather of the troposphere below. Observations of Northern Hemisphere warmings will be reviewed, including a critical assessment of the standard definitions of major and minor warmings. Experimental results from models of various complexity will be described that explore the influence of equatorial winds on the frequency and timing of warmings, with particular attention to the role of the QBO, the SAO and the solar cycle, all of which influence the equatorial winds in the upper stratosphere.