Preprints
https://doi.org/10.5194/acp-2020-1192
https://doi.org/10.5194/acp-2020-1192

  16 Dec 2020

16 Dec 2020

Review status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Spatial and temporal variability of the hydroxyl radical: Understanding the role of large-scale climate features and their influence on OH through its dynamical and photochemical drivers

Daniel C. Anderson1,2, Bryan N. Duncan2, Arlene M. Fiore3, Colleen B. Baublitz3, Melanie B. Follette-Cook2,4, Julie M. Nicely2,5, and Glenn M. Wolfe2 Daniel C. Anderson et al.
  • 1Universities Space Research Association, GESTAR, Columbia, MD, USA
  • 2Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD
  • 3Department of Earth and Environmental Sciences, Columbia University, Palisades, NY
  • 4Morgan State University, GESTAR, Baltimore, MD
  • 5Earth System Science Interdisciplinary Center, University of Maryland, College Park, College Park, MD

Abstract. The hydroxyl radical (OH) is the primary atmospheric oxidant, responsible for removing many important trace gases, including methane, from the atmosphere. Although robust relationships between OH drivers and modes of climate variability have been shown, the underlying mechanisms between OH and these climate modes, such as the El Niño Southern Oscillation (ENSO), have not been thoroughly investigated. Here, we use a chemical transport model to perform a 38-year simulation of atmospheric chemistry, in conjunction with satellite observations, to understand the relationship between tropospheric OH and ENSO, Northern Hemispheric modes of variability, the Indian Ocean Dipole, and monsoons. Empirical orthogonal function (EOF) and regression analyses show that ENSO is the dominant mode of global OH variability in the tropospheric column and upper troposphere, responsible for approximately 30 % of the total variance in boreal winter. Reductions in OH due to ENSO are centered over the tropical Pacific and Australia and can be as high as 10–15 % in the tropospheric column. The relationship between ENSO and OH is driven by changes in nitrogen oxides in the upper troposphere and changes in water vapor and O1D in the lower troposphere. While the spatial scale of the relationship between monsoons, other modes of variability, and OH are much smaller than ENSO, local changes in OH can be significantly larger than those caused by ENSO. These relationships also occur in multiple models that participated in the Chemistry Climate Model Initiative (CCMI), suggesting that the dependence of OH interannual variability on these well-known modes of climate variability is robust. Finally, modeled relationships between ENSO and OH drivers – such as carbon monoxide, water vapor, and lightning – closely agree with satellite observations. The ability of satellite products to capture the relationship between OH drivers and ENSO provides an avenue to an indirect OH observation strategy and new constraints on OH variability.

Daniel C. Anderson et al.

 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Daniel C. Anderson et al.

Daniel C. Anderson et al.

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Short summary
We demonstrate that large-scale climate features are the primary driver of year-to-year variability in simulated values of the hydroxyl radical, the primary atmospheric oxidant, over 1980–2018. The El Nino Southern Oscillation is the dominant mode of hydroxyl variability, resulting in large-scale global decreases in OH during El Nino events. Other climate modes, such as the Australian monsoon and the North Atlantic Oscillation, have impacts of similar magnitude, but on on more localized scales.
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