Partitioning of Ozone Loss Pathways in the Ozone Quasi-biennial Oscillation Simulated by a Chemistry-Climate Model

Abstract

Ozone loss pathways and their rates in the ozone quasi-biennial oscillation (QBO) simulated by a chemistry-climate model of the Meteorological Research Institute of Japan are evaluated by using an objective pathway analysis program (PAP). The analyzed chemical system contains catalytic cycles due to NOx, HOx, ClOx, Ox, and BrOx. PAP quantified the rates of all significant catalytic ozone loss cycles, and evaluated the partitioning among these cycles. The QBO amplitude of the sum of all cycles amounts to about 4 and 14 % of the annual mean of the total ozone loss rate at 10 and 20 hPa, respectively. The contribution of catalytic cycles to the QBO of the ozone loss rate is found to be as follows: NOx cycles contribute the largest fraction (50-85 %) of the QBO amplitude of the total ozone loss rate; HOx cycles are the second-largest (20-30 %) below 30 hPa and the third-largest (about 10 %) above 20 hPa; Ox cycles rank third (5-20 %) below 30 hPa and second (about 20 %) above 20 hPa; ClOx cycles rank fourth (5-10 %); and BrOx cycles are almost negligible. The relative contribution of the NOx and Ox cycles to the QBO amplitude of ozone loss differs by up to 10 and 20 %, respectively, from their contribution to the annual-mean ozone loss rate. The ozone QBO at 20 hPa is mainly driven by ozone transport, which then affects the ozone loss rate. In contrast, the ozone QBO at 10 hPa is driven chemically mainly by NOx and the temperature dependence of [O]/[O3], which results from the temperature dependence of the reaction O + O2 + M → O3 + M. In addition, the ozone QBO at 10 hPa is influenced by the overhead ozone column, which affects [O]/[O3] (through ozone photolysis) and the ozone production rate (through oxygen photolysis).

Simulations of Ozone Feedback Effects on the Equatorial Quasi-Biennial Oscillation with a Chemistry–Climate Model

“…As a result of the phase transition, the ozone QBO exhibits a dogleg-shaped pattern, being very different from the slanting stripe pattern of the zonal wind QBO. MRI-CCM realistically reproduced the ozone QBO including the phase transition and proved that both NO x and adiabatic heating due to the residual mean vertical motion were the dominant drivers in the photochemistry control [21].…”

“…The model used in this study is the CCM of the Meteorological Research Institute (MRI) of Japan (MRI-CCM). Specifications of the MRI-CCM are described in another paper [21,22] and references therein, so that only a brief description of its dynamics and chemistry is provided here. The dynamics module of MRI-CCM is an atmospheric spectral global model with triangular truncation, a maximum total wavenumber 42 (T42, about 2.8 • by 2.8 • in longitude and latitude grid space), and 81 layers in the terrain-following eta-coordinate with a lid at 0.01 hPa (about 80 km).…”

“…The MRI-CCM was integrated under the B2 scenario of the second phase Chemistry-Climate Model Validation Activity (CCMVal-2), i.e., REF-B2 [24], which specifies a timeevolving forcing by greenhouse gases (GHGs), ozone depleting substances (ODSs), and sea surface temperature (SST) and with fixed solar minimum and background aerosol conditions in the stratosphere. The integration was performed for about 50 years from 1970 until 2020 and referred to as a standard run (ST run), in which the QBO was realistically simulated in zonal wind and ozone [21]. In addition to the standard run, experiment runs were performed by changing the intensity of the radiative feedback of ozone.…”