Stratospheric contribution to the summertime high surface ozone events over the western united states

Abstract

The stratospheric influence on summertime high surface ozone ( O 3 ) events is examined using a twenty-year simulation from the Whole Atmosphere Community Climate Model. We find that O 3 transported from the stratosphere makes a significant contribution to the surface O 3 variability where background surface O 3 exceeds the 95th percentile, especially over western U.S. Maximum covariance analysis is applied to O 3 anomalies paired with stratospheric O 3 tracer anomalies to identify the stratospheric intrusion and the underlying dynamical mechanism. The first leading mode corresponds to deep stratospheric intrusions in the western and northern tier of the U.S., and intensified northeasterlies in the mid-to-lower troposphere along the west coast, which also facilitate the transport to the eastern Pacific Ocean. The second leading mode corresponds to deep intrusions over the Intermountain Regions. Both modes are associated with eastward propagating baroclinic systems, which are amplified near the end of the North Pacific storm tracks, leading to strong descents over the western U.S.

Enhancement of Arctic surface ozone during the 2020–2021 winter associated with the sudden stratospheric warming

“…Note that the chemical output of WACCM includes a stratospheric ozone tracer (O3S) that evolves via full chemistry in the stratosphere and then decays at a tropospheric chemistry rate once it crosses the tropopause. In the troposphere, O3S experiences the same loss rate as O 3 in the troposphere but is not affected by NO x photolysis as defined by the Chemistry-Climate Model Initiative (Tilmes et al 2016, Wang et al 2020. In general, O3S is a good indicator of stratosphere-totroposphere transport.…”

Higher‐Resolution Tropopause Folding Accounts for More Stratospheric Ozone Intrusions

“…The dominant mechanism for STT of air is tropopause folding (Stohl et al., 2003), wherein an intrusion of the stratosphere into the troposphere allows exchange between the two layers, typically influencing upper‐ and mid‐tropospheric ozone concentrations (Danielsen, 1968; Shapiro, 1980). Folding can also enable large stratospheric influence on near‐surface ozone in some regions—notably the eastern Mediterranean and Middle East (Akritidis et al., 2016; Tyrlis et al., 2014; Zanis et al., 2014), western United States (Langford et al., 1996, 2009; Langford & Reid, 1998; Lefohn et al., 2012; Wang et al., 2020), and Tibetan Plateau (X. L. Chen et al., 2011; X. Chen et al., 2013; Skerlak et al., 2019). But a more precise and systematic assessment of folding's role in ozone STT and relationship to tropospheric ozone than established by previous global studies (Beekmann et al., 1997; Boothe & Homeyer, 2017; Skerlak et al., 2014; Sprenger & Wernli, 2003) is possible due to new analysis tools.…”

“…mid-tropospheric ozone concentrations (Danielsen, 1968;Shapiro, 1980). Folding can also enable large stratospheric influence on near-surface ozone in some regions-notably the eastern Mediterranean and Middle East (Akritidis et al, 2016;Tyrlis et al, 2014;Zanis et al, 2014), western United States (Langford et al, 1996(Langford et al, , 2009Langford & Reid, 1998;Lefohn et al, 2012;Wang et al, 2020), and Tibetan Plateau (X. L. Chen et al, 2011;X. Chen et al, 2013;Skerlak et al, 2019).…”

Higher-resolution tropopause folding accounts for more stratospheric ozone intrusions

“…The dominant mechanism for STT of air is tropopause folding (Stohl et al, 2003), wherein an intrusion of the stratosphere into the troposphere allows exchange between the two layers, increasing local upper-and mid-tropospheric ozone concentrations (Danielsen, 1968;Shapiro, 1980). Folding is responsible for large stratospheric influence on surface ozone and air-quality-exceedance events in some regions-notably the summertime eastern Mediterranean, Middle East, and Afghanistan (Tyrlis et al, 2014;Zanis et al, 2014;Akritidis et al, 2016) and the wintertime and springtime western United States (Langford et al, 1996;Langford & Reid, 1998;Langford et al, 2009;Lefohn et al, 2012;Lin et al, 2012;Lin et al, 2015;Wang et al, 2020) and Tibetan Plateau X. L. Chen et al, 2011;X.…”

“…While no studies have as comprehensively addressed both folding and its relationship to ozone transport, several have indicated the significance of folding in such processes: localized observational and process-based studies have demonstrated strong ozone STT within intrusions, extending deep into the troposphere, and broader-scale studies have noted the important influence of stratospheric ozone on tropospheric ozone (Langford et al, 1996;Langford & Reid, 1998;Langford et al, 2009;Lefohn et al, 2012;Hess et al, 2015;Neu et al, 2014;Skerlak et al, 2019;Williams et al, 2019;Wang et al, 2020).…”