Examining the stratospheric response to the solar cycle in a coupled WACCM simulation with an internally generated QBO
Abstract. The response of the stratosphere to the combined interaction of the quasi-biennial oscillation (QBO) and the solar cycle in ultraviolet (UV) radiation, and the influence of the solar cycle on the QBO, are investigated using the Whole Atmosphere Community Climate Model (WACCM). Transient simulations were performed beginning in 1850 that included fully interactive ocean and chemistry model components, observed greenhouse gas concentrations, volcanic eruptions, and an internally generated QBO. Over the full length of the simulations we do not find a solar cycle modulation of either the QBO period or amplitude. We also do not find a persistent wintertime UV response in polar stratospheric geopotential heights when stratifying by the QBO phase. Over individual ~40 year periods of the simulation, a statistically significant correlation is sometimes found between the northern polar geopotential heights in February and UV irradiance during the QBO's westerly phase. However, the sign of the correlation varies over the simulation, and is never significant during the QBO's easterly phase. Complementing this is the analysis of four simulations using a QBO prescribed to match observations over the period 1953–2005. Again, no consistent correlation is evident. In contrast, over the same period, meteorological reanalysis shows a strong positive correlation during the QBO westerly phase, although it weakens as the period is extended. The results raise the possibility that the observed polar solar–QBO correlation may have occurred because of the relatively short data record and the presence of additional external forcings rather than a direct solar–QBO interaction.