Relationship of the quasi-biennial oscillation to the stratospheric signature of the solar cycle

Abstract

Records of analyzed dynamical structure indicate a correlation with the 11-year variation of solar flux F s. In the monthly record, anomalous temperature maximizes in the stratosphere, with symmetry about the equator. However, even there, the signature is weak and scarcely significant. Sampling the same record around solstice and during extremal phases of the QBO sharply enhances the strength, significance, and symmetry of the solar signature. In the tropics the solar signature follows from a decadal modulation in the frequency of the quasi-biennial oscillation (QBO). In instantaneous power spectra the modulation is manifested to either side of the QBO's mean frequency, in two spectral peaks where the QBO dwells: one at (24 months) -1, reflecting a biennial oscillation (BO), and another at (36 months) -1. Intrinsic to the QBO, those peaks are separated from its mean frequency by ∼11 yr -1. The decadal modulation produces a strong correlation to F s and, through the residual circulation of the QBO, symmetry about the equator. Augmenting this high-frequency contribution is a low-frequency contribution to the solar signature, one that simply tracks the 11-year variation of F s. Characterized by broad symmetry about the equator, it reflects the involvement of the Brewer-Dobson circulation. Accompanying anomalous temperature in the subtropics is a stronger signature over the winter pole, where interannual variance is large. Discovered by Labitzke and van Loon (1988), that solar signature reflects anomalous downwelling of the Brewer-Dobson circulation. As strong as the RMS interannual variation, it is accounted for entirely by the high-frequency contribution associated with the QBO. The extratropical signature is shown to follow through the BO, which is transmitted poleward by planetary waves. Salient features of the observed behavior are reproduced by a simple model of the QBO's modulation and its interaction with the extratropical circulation. Copyright 2006 by the American Geophysical Union.