WCD-27. The response of the North Pacific jet and stratosphere-to-troposphere mass transport over western North America to RCP8.5 climate forcing

Deep exchanges of ozone rich stratospheric air are prevalent over Western North America during spring. During this time the jet-stream over the North Pacific transitions from its strong, narrow, and contiguous winter structure to its weaker and latitudinally broad summer structure. The change in upper tropospheric Rossby wave breaking occurring during this spring transition of the jet mixes stratospheric air deeply into the troposphere, even into the planetary boundary layer. While recent research shows how internal climate variability affects these deep stratosphere to troposphere transport (STT) events, it is not yet known how climate change will influence the spring transition of the North Pacific jet and the associated STT. In this study, the spring transition of the North Pacific jet is compared in global climate model experiments forced with preindustrial control conditions and worst-case scenario RCP8.5 conditions. The end-of-century North Pacific jet-stream is far stronger and narrower in response to worst-case scenario climate change. A tracer of stratospheric ozone, O3S, is used to quantify changes in STT of ozone. Tropospheric O3S increases by 40% in the RCP8.5 experiment relative to the preindustrial experiment. The spring transition of the North Pacific jet enhances the amount of O3S entering the troposphere over Western North America in an RCP8.5 future. More O3S is able to enter the troposphere because there is a marked increase in lower stratospheric ozone in response to the acceleration of the Brewer Dobson Circulation that is concurrent with elevated atmospheric carbon dioxide concentrations and warmer oceans. Additional sensitivity experiments are used to investigate whether it is the future sea surface temperatures or future greenhouse gasses that are most important for modifying the lower stratospheric ozone abundance.