The combined influence of ENSO and PDO on the spring UTLS ozone variability in South America
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The combined influence of ENSO and PDO on the spring UTLS ozone variability in South America Brandi L. Gamelin1 · Leila M. V. Carvalho1,2 · Mary Kayano3 Received: 25 January 2020 / Accepted: 13 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Ozone in the upper troposphere–lower stratosphere (UTLS) is primarily regulated by tropospheric dynamics. Understanding mechanisms driving ozone variability at the UTLS is crucial to evaluate the transport of mass to and from the lower stratosphere. The El Niño-Southern Oscillation (ENSO) is the primary coupled mode acting on interannual timescales modulating tropospheric circulation worldwide. ENSO teleconnections can depend on the phases of the Pacific Decadal Oscillation (PDO) and on the characteristics of the warming over central and eastern tropical Pacific. This study investigates the role of ENSO on UTLS ozone variability with focus on South America and examines patterns of teleconnections in the two recent warm (1980–1997) and cool (1998–2012) PDO phases. The dominant mode of ozone variability is identified by applying a principal component analysis (PCA) to modern-era retrospective analysis for research and applications, Version 2 (MERRA-2) ozone data from September–November (SON). SON is the season with the largest UTLS ozone variance over South America. The first mode resembles a Rossby wave train across South America with spatial patterns dependent on PDO phase. We show that the ENSO teleconnections and respective influences on SON UTLS ozone are stronger during the cool PDO when ENSO and PDO are mostly in phase. Additionally, the strength of the ENSO teleconnection appears to depend on patterns of SST anomalies over tropical Pacific. The decadal variability in the ENSO-PDO relationships and teleconnections with the Southern Hemisphere resulted in a shift in upper tropospheric circulation in tropical and subtropical regions of South America. Keywords ENSO · PDO · ENSO teleconnections · Upper troposphere–lower stratosphere ozone · Rossby wave trains · South America
1 Introduction Ozone in the lower stratosphere is primarily regulated by cross tropopause exchanges associated with tropospheric circulation processes. In the stratosphere, ozone regulates the amount of ultraviolet radiation that reaches Earth’s surface and is the primary driver of globally averaged stratospheric temperature trends (Steinbrecht et al. 2003; WMO * Brandi L. Gamelin [email protected] 1
Department of Geography, University of California, Santa Barbara, CA 93106, USA
2
Earth Research Institute, University of California, Santa Barbara, USA
3
Instituto Nacional de Pesquisas Espaciais, Centro de Previsão de Tempo E Estudos Climáticos, São José dos Campos, Brazil
Ozone Assessment 2011). Stratospheric ozone variability is related to three dynamical processes: (1) upwelling/downwelling associated with the Brewer Dobson Circulation (BDC)—the general stratospheric circulation pattern; (2) stratospheric zonal winds shift from easterlies to westerlies,
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