Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends
Over 20 years of stratospheric NO<sub>2</sub> vertical column density (VCD) data from ground-based zenith DOAS spectrometers were used for trend analysis, specifically, via multiple linear regression. Spectrometers from the Network for the Detection of Atmospheric Composition Change (...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/17/13373/2017/acp-17-13373-2017.pdf |
| Summary: | Over 20 years of stratospheric NO<sub>2</sub> vertical column density (VCD)
data from ground-based zenith DOAS spectrometers were used for trend
analysis, specifically, via multiple linear regression. Spectrometers from
the Network for the Detection of Atmospheric Composition Change (NDACC) cover
the subtropical latitudes in the Northern Hemisphere (Izaña,
28° N), the southern Subantarctic (Ushuaia, 55° S) and
Antarctica (Marambio, 64° S, and Belgrano, 78° S). The
results show that for the period 1993–2014, a mean positive decadal trend of
+8.7 % was found in the subtropical Northern Hemisphere stations,
and negative decadal trends of −8.7 and −13.8 % were found in
the Southern Hemisphere at Ushuaia and Marambio, respectively; all trends are
statistically significant at 95 %. Belgrano only shows a significant
decadal trend of −11.3 % in the summer/autumn period. Most of the
trends result from variations after 2005. The trend in the diurnal build-up
per hour (DBU) was used to estimate the change in the rate of
N<sub>2</sub>O<sub>5</sub> conversion to NO<sub>2</sub> during the day. With minor
differences, the results reproduce those obtained for NO<sub>2</sub>. The
trends computed for individual months show large month-to-month variability.
At Izaña, the maximum occurs in December (+13.1 %), dropping
abruptly to lower values in the first part of the year. In the Southern
Hemisphere, the polar vortex dominates the monthly distributions of the
trends. At Marambio, the maximum occurs in mid-winter (−21 %),
whereas at the same time, the Ushuaia trend is close to its annual minimum
(−7 %). The large difference in the trends at these two relatively
close stations suggests a vortex shift towards the Atlantic/South American
area over the past few years. Finally, the hemispheric asymmetry obtained in
this work is discussed in the framework of the results obtained by previous
works that considered tracer analysis and Brewer–Dobson circulation. The
results obtained here provide evidence that the NO<sub>2</sub> produced by
N<sub>2</sub>O decomposition is not the only cause of the observed trend in
the stratosphere and support recent publications pointing to a dynamical
redistribution starting in the past decade. |
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| ISSN: | 1680-7316 1680-7324 |