Simulations of stratospheric flow regimes during northern hemisphere winter

The interaction of the solar influence and the Quasi-Biennial Oscillation (QBO) on the northern hemisphere winter circulation and temperatures is investigated. If we can reproduce and understand this interaction in a relatively simple model of the atmosphere it should help to identify the important mechanisms that enable the solar influence to extend to the lower atmosphere and influence our climate. A stratosphere-mesosphere model of the atmosphere has been employed to carry out a wide range of regime studies to determine the sensitivity of stratospheric sudden warmings to various forcings, including the amplitude of tropospheric planetary wave forcing, the QBO and a simple representation of the solar-induced zonal wind anomaly. The results suggest that warmings are sensitive to the background flow and forcing in the subtropical northern upper stratosphere in early winter. This is the region in which the Aleutian High is initiated and thence grows in amplitude, extending polewards and downwards as the warming evolves. Both QBO and solar anomalies of similar amplitude are found in this region of the atmosphere and therefore have the potential to interact with each other. Published by Elsevier Ltd on behalf of COSPAR