Abstract
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.
Highlights
Beginning in the 1980s, Labitzke (1987) stratified the mean winter temperatures at 30 hPa over the North Pole by the phase of the quasi-biennial oscillation (QBO) and the January sunspot numbers, a measure of solar cycle variability
Results were presented from two WACCM4 simulations including fully interactive ocean, sea ice, and chemistry components, varying solar spectral irradiance, volcanic forcing, and an internally generated QBO
While the temperature changes are at the lower end compared with ERA-40 data (Chiodo et al, 2012), the pattern is consistent with observations and past modeling studies
Summary
Beginning in the 1980s, Labitzke (1987) stratified the mean winter temperatures at 30 hPa over the North Pole by the phase of the QBO (quasi-biennial oscillation) and the January sunspot numbers, a measure of solar cycle variability. A number of studies have investigated the relationship using model simulations that incorporated a prescribed, parameterized, or internally generated QBO (e.g., Rind and Balachandran, 1995; Gray et al, 2004; Matthes et al, 2004; McCormack et al, 2007; Schmidt et al, 2010) These models have not been able to reproduce all aspects, the studies indicate that there is a circulation response in the polar vortex that depends on both QBO phase and the 11 year solar cycle. A 150 year model simulation study by McCormack et al (2007) using a parameterized QBO and UV (ultraviolet) variations showed a shortened QBO west period by about 3 months at solar maximum compared to solar minimum.
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