Abstract
Some key photochemical uncertainties that cannot be readily eliminated by current observations translate into a range of stratospheric O3abundances in the tens of percent. The uncertainty in O3production due to that in the cross sections for O2in the Hertzberg continuum is studied here with the NCAR Community Atmosphere Model, which allows for interactive climate and ozone chemistry. A min‐max range in the O2cross sections of 30%, consistent with current uncertainties, changes O3abundances in the lower tropical stratosphere by up to 30%, with a relatively smaller and opposite change above 30 hPa. Here we have systematically examined the changes in the time‐mean state, the seasonal cycle, and the interannual variability of the temperature and circulation associated with the ±30% change in O2cross sections. This study points to the important role of O3in the lower tropical stratosphere in determining the physical characteristics of the tropical tropopause layer. Reducing O2cross sections by 30% increases ozone abundances which warms the lower stratosphere (60°S −60°N; 2 K maximum at equator) and lowers the tropopause height by 100–200 m (30°S –30°N). The large‐scale warming leads to enhanced stratification near the tropopause which reduces upward wave propagation everywhere except for high latitudes. The lowermost tropical stratosphere is better ventilated during austral winter. The annual cycle of ozone is amplified. The interannual variability of the winter stratospheric polar vortices also increases, but the mechanism involves wave‐mean flow interaction, and the exact role of ozone in it needs further investigation.
Highlights
We use the canonical laboratory cross-section measurements [Yoshino et al, 1988], and in our uncertainty cases, we reduce or increase these values by 30% over the wavelengths 202–242 nm as an estimate of 90% confidence interval in these cross sections based on the uncertainty factor 1.2 in Sander et al [2011] with 20% being interpreted as 1- uncertainty from the mean
[22] we examine the equatorial annual and semiannual cycles simulated in CAM5 and explore if the perturbation of ozone production has any impact on these
[33] We hypothesize that in Sfast-Ctrl and Mozart-O2ji, the temperature near the 72 hPa at equator is more controlled by the tropical convection from below and less influenced by the wave forcing from midlatitudes through Brewer-Dobson circulation (BDC)
Summary
[2] Tremendous progress has been made in separate studies of atmospheric chemistry, stratospheric dynamics, and climate change. We use an atmospheric chemistry-climate model to calculate how current uncertainties in the primary photochemical production of O3 can change ozone abundances in the lower tropical stratosphere and, through. [6] In this study, we examine the stratospheric climate statistics from alternative stratospheric O3 chemistry, defined by the uncertainty range in O2 cross sections, within the Community Atmosphere Model version 5 (CAM5 hereafter) [Gettelman et al, 2012]. Stratospheric ozone is simulated by Linoz (Linearized stratospheric ozone) version 2 [Hsu and Prather, 2009] This CAM-Linoz model is self-consistent in that the circulation determines stratosphere O3, and this O3 is used in the radiative calculation that forces the circulation.
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