A216-0005
Solar 11-Year Cycle Signal in Nitrogen Dioxide – Similarities and Discrepancies between Model and Observations from NDACC stations

Wednesday, 16 December 2020
Poster
Shuhui Wang, University of California Los Angeles, JIFRESSE, Los Angeles, CA, United States, King-Fai Li, University of California Riverside, Environmental Sciences, Riverside, CA, United States, Diana Zhu, Harvard University, Cambridge, MA, United States, Stanley P Sander, NASA Jet Propulsion Laboratory, Pasadena, CA, United States, Yuk L Yung, California Institute of Technology, Pasadena, CA, United States, Andrea Pazmiño, CNRS, UVSQ, LATMOS, Guyancourt, France and Richard Querel, National Institute of Water & Atmospheric Research (NIWA), Lauder, New Zealand
Abstract:
Stratospheric NO2 is mainly produced by the reaction of N2O with photochemically produced O(1D) and, therefore, is expected to vary with changes in UV irradiance during the solar cycle. NO2, together with NO, play an important role in controlling stratospheric ozone through the catalytic NOx reaction cycle. Understanding the changes in NO2 due to the natural solar forcing is thus important for a better understanding of the complex ozone changes as a result of both anthropogenic and natural factors. It also provides insights to better predict future changes in ozone and the corresponding impacts on the climate.

Previous studies on this topic, often limited by the relatively short continuous data, show puzzling results. The effect of the 1991 Pinatubo eruption might have caused interference in the analysis. In this study, we examine the NO2 vertical column density (VCD) data from the Network for the Detection of Atmospheric Composition Change (NDACC). Data collected at 16 stations with continuous long-term observations covering the most recent Solar Cycles 23 and 24 were analyzed. The years with possible interferences from the Pinatubo eruption were excluded. We found positive correlations between changes in NO2 and solar Lyman-α over most Northern Hemispheric stations and very small or negative correlations over most Southern Hemispheric stations (Figure 1). The varying NO2 responses from one location to another are likely due to different geo-locations (latitude and altitude). In particular, two high-altitude stations show the strongest positive NO2 solar-cycle signals.

Our 1D chemical-transport model calculations reveal the altitude dependence of NO2 response to the solar cycle due to the UV-sensitive chemical kinetics (Figure 2). NO2 solar-cycle variability is suggested to play an important role controlling O3 at ~20 – 60 km, while OH solar-cycle variability controls O3 at 40 – 90 km. While observations show both positive and negative NO2 responses to solar forcing, the 1D model predicts negative NO2 responses throughout the middle atmosphere. 3D global model results suggest complex roles of dynamics in addition to photochemistry. The energetic particle-induced NO2 variabilities could also contribute significantly to the NO2 variability during solar cycles at high-latitude stations.

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