Dynamical and Trace Gas Responses of the Quasi‐Biennial Oscillation to Increased CO₂

Abstract

The Quasi-Biennial Oscillation (QBO) dominates interannual variability in the tropical stratosphere (Baldwin et al., 2001). Its origin in wave-driven angular momentum transport is well-appreciated, as initial theoretical work (e.g.,

Response of the Quasi‐Biennial Oscillation to Historical Volcanic Eruptions

“…We attribute this limitation to the ensemble's weak momentum flux due to convection. Specifically, the zonal wind tendency due to convective gravity wave drag is in-phase with the total tendency, and short-term variations in phase speed are positively correlated with momentum flux due to convection (DallaSanta et al, 2021). Ignoring all other contributions to the wind tendencies, one can thus derive a lower bound on the QBO period resulting solely from momentum deposition associated with parameterized convective gravity wave drag, as detailed in Appendix A.…”

“…for them to modify the QBO at higher levels (DallaSanta et al, 2021), even after the aerosols have decayed.…”

“…We estimate a lower bound on the model's QBO period. Considering the composited momentum budget (DallaSanta et al, 2021), the downward propagation of the QBO is predominantly driven by tropical momentum flux due to convection, which is in-phase with the total tendency. Suppose that all of this momentum flux, and only this momentum flux, is used to drive the QBO.…”

The impact of increasing stratospheric radiative damping on the quasi-biennial oscillation period

“…It is not unexpected because the infrared radiative cooling by ozone is significantly smaller than that by CO 2 (refer to Fig. 1 in Dickinson, 1973), and, as a result, the 15 %-20 % increases in the ozone mixing ratio will not make a noticeable difference. Since the monthly and zonal mean 2D ozone concentrations are specified in about 80 % of the CMIP5 models (Cionni et al, 2011), and the monthly mean 3D ozone data are employed in many CMIP6 models (Keeble et al, 2020), it is expected that the change in the radiative damping due to the increase in ozone in response to the doubled CO 2 only marginally impacts the QBO periods in those models that do not include an interactive chemistry.…”

“…In order to rigorously quantify the relationship of the Newtonian cooling coefficient at any altitude z between the reference and doubled CO 2 , we follow Dickinson (1973) in using a radiative-transfer model to calculate Q 1 (T ) for a reference temperature profile T (z) and Q 1 (T + δ) for T (z) + δ, where a small perturbation δT = 0.1 K, with T (z) being the 1976 US standard atmosphere. Our radiative-transfer computations use the MODTRAN gas absorption database with 0.1 cm −1 spectral resolution (Jin et al, 2019;Berk et al, 2008).…”