The Role of Convection in Tropical Ozone Trends (1998-2018) Based on SHADOZ Profiles
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2020-06-18
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
Quantifying variability in the lowermost stratosphere (LMS) is important because of feedbacks among changing temperature,
dynamics and species like ozone. We used reprocessed Southern Hemisphere Additional Ozonesondes data from 1998-2018 in
a Multiple Linear Regression (MLR) model to analyze variability and trends in free tropospheric (FT) and LMS ozoneacross
five well-distributed tropical regions. The MLR also computed trends in a proxy for convection as determined from laminae in
each ozonesonde-radiosonde pair. Only the equatorial Americas exhibits statistically significant annual trends in FT or LMS
ozone. At the other sites, ozonetrends occur in isolated layers during months when convection has changed, February-April
or July-November. Our results imply that large FT ozone increases reported for populated tropical areas may be caused by
growing pollution overlying smaller changes caused by perturbed dynamics. They also provide regional data for evaluating LMS
ozonetrends based on zonal averages of often sparse satellite measurements