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| Titel |
A new method to detect long term trends of methane (CH4) and nitrous oxide (N2O) total columns measured within the NDACC ground-based high resolution solar FTIR network |
| VerfasserIn |
J. Angelbratt, J. Mellqvist, T. Blumenstock, T. Borsdorff, S. Brohede, P. Duchatelet, F. Forster, F. Hase, E. Mahieu, D. Murtagh, A. K. Petersen, M. Schneider, R. Sussmann, J. Urban |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 13 ; Nr. 11, no. 13 (2011-07-01), S.6167-6183 |
| Datensatznummer |
250009879
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| Publikation (Nr.) |
 copernicus.org/acp-11-6167-2011.pdf |
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| Zusammenfassung |
| Total columns measured with the ground-based solar FTIR technique are highly
variable in time due to atmospheric chemistry and dynamics in the atmosphere
above the measurement station. In this paper, a multiple regression model
with anomalies of air pressure, total columns of hydrogen fluoride (HF) and
carbon monoxide (CO) and tropopause height are used to reduce the variability
in the methane (CH4) and nitrous oxide (N2O) total columns to
estimate reliable linear trends with as small uncertainties as possible. The
method is developed at the Harestua station (60° N,
11° E, 600 m a.s.l.) and used on three other European FTIR
stations, i.e. Jungfraujoch (47° N, 8° E,
3600 m a.s.l.), Zugspitze (47° N, 11° E,
3000 m a.s.l.), and Kiruna (68° N, 20° E,
400 m a.s.l.). Linear CH4 trends between
0.13 ± 0.01-0.25 ± 0.02 % yr−1 were estimated for all
stations in the 1996-2009 period. A piecewise model with three separate
linear trends, connected at change points, was used to estimate the short
term fluctuations in the CH4 total columns. This model shows a growth in
1996–1999 followed by a period of steady state until 2007. From 2007 until
2009 the atmospheric CH4 amount increases between
0.57 ± 0.22–1.15 ± 0.17 % yr−1. Linear N2O trends
between 0.19 ± 0.01–0.40 ± 0.02 % yr−1 were estimated
for all stations in the 1996-2007 period, here with the strongest trend at
Harestua and Kiruna and the lowest at the Alp stations. From the N2O
total columns crude tropospheric and stratospheric partial columns were
derived, indicating that the observed difference in the N2O trends
between the FTIR sites is of stratospheric origin. This agrees well with the
N2O measurements by the SMR instrument onboard the Odin satellite
showing the highest trends at Harestua, 0.98 ± 0.28 % yr−1,
and considerably smaller trends at lower latitudes,
0.27 ± 0.25 % yr−1. The multiple regression model was
compared with two other trend methods, the ordinary linear regression and a
Bootstrap algorithm. The multiple regression model estimated CH4 and
N2O trends that differed up to 31 % compared to the other two
methods and had uncertainties that were up to 300 % lower. Since the
multiple regression method were carefully validated this stresses the
importance to account for variability in the total columns when estimating
trend from solar FTIR data. |
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