Origin and variability of upper tropospheric nitrogen oxides and ozone at northern mid-latitudes
Year-long measurements of NOx and ozone performed during the NOXAR project are compared to results from the ECHAM4.L39(DLR)/CHEM (E39/C) and GISS coupled chemistry-climate models. The measurements were taken on flights between Europe and the eastern United States and between Europe and the Far East in the latitude range 40-65°N. Our comparison concentrates on the upper troposphere and reveals strong longitudinal variations in seasonal mean NOx of more than 200pptv, which both models are able to reproduce qualitatively. Vertical profiles show maximum NOx values 2-3km below the tropopause ('E-shape') with a strong seasonal cycle. E39/C simulates a maximum located at the tropopause and with a reasonable seasonal cycle. The GISS model reproduces the seasonal cycle but not the profile's shape due to its coarser vertical resolution. A comparison of NOx frequency distributions reveals that both models are capable of reproducing the observed variability, except that E39/C shows no very high NOx mixing ratios.Both models show that lightning and surface NOx emissions contribute the most to the seasonal cycle of NOx at tropopause altitudes. The impact of lightning in the upper troposphere does not vary strongly with altitude, whereas the impact of surface emissions decreases with altitude. Among all sources, lightning contributes the most to the variability of NOx in the upper troposphere in northern mid-latitudes during summer. Copyright © 2001 Elsevier Science Ltd.
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Citation
Published In
DOI
ISSN
Publication Date
Volume
Issue
Start / End Page
Related Subject Headings
- Meteorology & Atmospheric Sciences
- 4011 Environmental engineering
- 3702 Climate change science
- 3701 Atmospheric sciences
- 0907 Environmental Engineering
- 0401 Atmospheric Sciences
- 0104 Statistics