Modulation of the Period of the Quasi-Biennial Oscillation by the Solar Cycle
Abstract
The authors examine the mechanism of solar cycle modulation of the Quasi-Biennial Oscillation (QBO) period using the Two-and-a-Half-Dimensional Interactive Isentropic Research (THINAIR) model. Previous model results (using 2D and 3D models of varying complexity) have not convincingly established the proposed link of longer QBO periods during solar minima. Observational evidence for such a modulation is also controversial because it is only found during the period from the 1960s to the early 1990s, which is contaminated by volcanic aerosols. In the model, 200- and 400-yr runs without volcano influence can be obtained, long enough to establish some statistical robustness. Both in model and observed data, there is a strong synchronization of the QBO period with integer multiples of the semiannual oscillation (SAO) in the upper stratosphere. Under the current level of wave forcing, the period of the QBO jumps from one multiple of SAO to another and back so that it averages to 28 months, never settling down to a constant period. The "decadal" variability in the QBO period takes the form of "quantum" jumps; these, however, do not appear to follow the level of the solar flux in either the observation or the model using realistic quasi-periodic solar cycle (SC) forcing. To understand the solar modulation of the QBO period, the authors perform model runs with a range of perpetual solar forcing, either lower or higher than the current level. At the current level of solar forcing, the model QBO period consists of a distribution of four and five SAO periods, similar to the observed distribution. This distribution changes as solar forcing changes. For lower (higher) solar forcing, the distribution shifts to more (less) four SAO periods than five SAO periods. The record-averaged QBO period increases with the solar forcing. However, because this effect is rather weak and is detectable only with exaggerated forcing, the authors suggest that the previous result of the anticorrelation of the QBO period with the SC seen in short observational records reflects only a chance behavior of the QBO period, which naturally jumps in a nonstationary manner even if the solar forcing is held constant, and the correlation can change as the record gets longer.
Additional Information
© 2009 American Meteorological Society. (Manuscript received 22 September 2008, in final form 23 February 2009) This work was supported in part by NASA Grants NAG1-1806 and NNG04GN02G to the California Institute of Technology. K. K. Tung's research was supported by NSF Grants ATM 0332364 and ATM 0808375 to the University of Washington. We thank A. Ruzmaikin and J. Feynman for their useful discussions. We also acknowledge help in improving the paper from M. C. Liang, N. Heavens, X. Guo, A. Soto, T. Lee, X. Zhang, P. S. Jiang, Y. C. Chen, D. Yang, and C. D. Camp.Attached Files
Published - Le2009p5703J_Atmos_Sci.pdf
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Additional details
- Eprint ID
- 15325
- Resolver ID
- CaltechAUTHORS:20090826-112852185
- NAG1-1806
- NASA
- NNG04GN02G
- NASA
- ATM 0332364
- NSF
- ATM 0808375
- NSF
- Created
-
2009-09-11Created from EPrint's datestamp field
- Updated
-
2021-11-08Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences