The Impact of Nudging the Stratospheric Quasi-Biennial Oscillation on the Tropical Circulation in the UKMO Unified Model

The influence of the stratospheric quasi-biennial oscillation (QBO) on the tropical circulation, convection, monsoons and the Inter-tropical Convergence Zone is investigated in nudging experiments using the UK Met Office Hadley Centre global climate model. In these experiments, the zonal wind in the equatorial stratosphere is relaxed towards reanalysis to correct for biases in the representation of the QBO. Atmosphere-only and coupled ocean-atmosphere configurations with nudging are compared against free-running control simulations.The simulations with a nudged stratosphere produce a stronger and more realistic variability of the equatorial and subtropical tropopause height and temperature associated with the QBO than in the control simulations. The effect of the QBO over tropical convection, monsoon regions and the ITCZ is investigated and compared between control and nudged simulations.