22 Nov 2022
22 Nov 2022
Status: this preprint is currently under review for the journal ACP.

The response of the North Pacific jet and stratosphere-to-troposphere transport of ozone over western North America to RCP8.5 climate forcing

Dillon Elsbury1,2, Amy H. Butler2, John R. Albers1,3, Melissa L. Breeden1,3, and Andrew O'Neil Langford2 Dillon Elsbury et al.
  • 1Cooperative Institute for Research in Environmental Sciences, Boulder, 80305, United States
  • 2National Oceanic and Atmospheric Administration Chemical Sciences Laboratory, Boulder, 80305, United States
  • 3National Oceanic and Atmospheric Administration Physical Sciences Laboratory, Boulder, 80305, United States

Abstract. Stratosphere-to-troposphere transport (STT) is an important source of ozone for the troposphere, particularly over western North America. STT in this region is predominantly controlled by a combination of the variability and location of the Pacific jet stream and the amount of ozone in the lower stratosphere, two factors which are likely to change if greenhouse gas concentrations continue to increase. Here we use Whole Atmosphere Community Climate Model experiments with a tracer of stratospheric ozone (O3S) to study how end-of-the-century Representative Concentration Pathway (RCP) 8.5 sea surface temperatures (SSTs) and greenhouses gases (GHGs), in isolation and in combination, influence STT of ozone over western North America relative to a preindustrial control background state.

We find that O3S increases up to 39 % at 700 hPa over western North America in response to RCP8.5 forcing with the largest increases occurring during late winter and tapering off somewhat during spring and summer. When this response is decomposed into the contributions made by future SSTs and GHGs, the latter are found to be primarily responsible for these O3S changes. Both the future SSTs and the future GHGs accelerate the Brewer Dobson circulation, which increases extratropical lower stratospheric ozone mixing ratios. While the GHGs promote a more zonally symmetric lower stratospheric ozone change due to enhanced ozone production and some transport, the SSTs increase lower stratospheric ozone predominantly over the North Pacific via transport associated with a stationary planetary-scale wave. Ozone accumulates in the trough of this anomalous wave and is reduced over the wave’s ridges, illustrating that the composition of the lower stratospheric ozone reservoir in the future is dependent on the phase and position of the stationary planetary-scale wave response to future SSTs, in addition to the poleward mass transport provided by the accelerated Brewer-Dobson Circulation. In addition, the future SSTs account for most changes to the large-scale circulation in the troposphere and stratosphere compared to the effect of future greenhouse gases. These changes include modifying the position and speed of the future North Pacific jet, lifting the tropopause, accelerating both the Brewer-Dobson Circulation’s shallow and deep branches, and enhancing two-way isentropic mixing in the stratosphere.

Dillon Elsbury et al.

Status: open (until 04 Jan 2023)

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Dillon Elsbury et al.

Dillon Elsbury et al.


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Short summary
One of the global ‘hot-spots’ where stratosphere to troposphere transport (STT) of ozone takes place is over western North America (WNA). However, we do not know how or if STT over WNA will change in response to climate change. Using climate model experiment forced with ‘worst-case scenario’ Representative Concentration Pathway-8.5 (RCP8.5) climate change, we find that changes in transport and net chemical production of ozone in the lower stratosphere promote more STT over WNA in the future.