Synchronisation of the equatorial QBO by the annual cycle in tropical upwelling in a warming climate

Abstract

The response of the period of the quasi-biennial oscillation (QBO) to increases in tropical upwelling are considered using a one-dimensional model. We find that the imposition of the annual cycle in tropical upwelling creates substantial variability in the period of the QBO. The annual cycle creates synchronisation regions in the wave forcing space, within which the QBO period locks onto an integer multiple of the annual forcing period. Outside of these regions, the QBO period undergoes discrete jumps as it attempts to find a stable relationship with the oscillator forcing. The resulting set of QBO periods can be either discrete or broad-banded, depending on the intrinsic period of the QBO.We use the same model to study the evolution of the QBO period as the strength of tropical upwelling increases, as would be expected in a warmer climate. The QBO period lengthens and migrates closer towards 36-and 48-month locking regions as upwelling increases. The QBO period does not vary continuously with increased upwelling, however, but instead transitions through a series of two-and three-cycles before becoming locked to the annual cycle. Finally, some observational evidence for the cyclical behaviour of the QBO periods in the real atmosphere is presented.

Global climate modeling of Saturn’s atmosphere. Part IV: Stratospheric equatorial oscillation

“…Idealized terrestrial QBO simulations show that the seasonal cycle could lock the equatorial oscillation period to an integer multiple of the annual cycle period (Rajendran et al, 2016). In our reference simulation, the QBO-like oscillation period is nearly the observed mean period, namely about half a Saturn year.…”

Overview of experiment design and comparison of models participating in phase 1 of the SPARC Quasi-Biennial Oscillation initiative (QBOi)

“…Other key questions concerning simulation of the QBO regard its possible synchronization with other modes of variability, such as the annual cycle (e.g. Rajendran et al, 2016) and El Niño-Southern Oscillation (e.g. Christiansen et al, 2016), the QBO's predictability (e.g.…”

Overview of experiment design and comparison of models participating in phase 1 of the SPARC Quasi-Biennial Oscillation initiative (QBOi)

“…In addition Yao and Jablonowski (2015) identified a sensitivity to the choice of dynamical core. Other key questions concerning 5 simulation of the QBO lie with its possible synchronisation with other modes of variability such as the annual cycle (e.g., Rajendran et al, 2016) and El Niño-Southern Oscillation (e.g., Christiansen et al, 2016), with the QBO's predictability (e.g., Pohlmann et al, 2013;Scaife et al, 2014) and finally with the robustness of the QBO response to climate change (e.g. Kawatani and Hamilton, 2013;Schirber et al, 2015).…”