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| Titel |
Impact of sampling frequency in the analysis of tropospheric ozone observations |
| VerfasserIn |
M. Saunois, L. Emmons, J.-F. Lamarque, S. Tilmes, C. Wespes, V. Thouret, M. Schultz |
| 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 ; 12, no. 15 ; Nr. 12, no. 15 (2012-08-01), S.6757-6773 |
| Datensatznummer |
250011355
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| Publikation (Nr.) |
 copernicus.org/acp-12-6757-2012.pdf |
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| Zusammenfassung |
| Measurements of ozone vertical profiles are valuable for the evaluation of
atmospheric chemistry models and contribute to the understanding of the
processes controlling the distribution of tropospheric ozone. The longest
record of ozone vertical profiles is provided by ozone sondes, which have a
typical frequency of 4 to 12 profiles a month. Here we quantify the
uncertainty introduced by low frequency sampling in the determination of
means and trends. To do this, the high frequency MOZAIC (Measurements of
OZone, water vapor, carbon monoxide and nitrogen oxides by in-service AIrbus
airCraft) profiles over airports, such as Frankfurt, have been subsampled at
two typical ozone sonde frequencies of 4 and 12 profiles per month. We found
the lowest sampling uncertainty on seasonal means at 700 hPa over Frankfurt,
with around 5% for a frequency of 12 profiles per month and 10% for a 4
profile-a-month frequency. However the uncertainty can reach up to 15 and
29% at the lowest altitude levels. As a consequence, the sampling uncertainty
at the lowest frequency could be higher than the typical 10% accuracy of
the ozone sondes and should be carefully considered for observation
comparison and model evaluation. We found that the 95% confidence limit on
the seasonal mean derived from the subsample created is similar to the
sampling uncertainty and suggest to use it as an estimate of the sampling
uncertainty. Similar results are found at six other Northern Hemisphere
sites. We show that the sampling substantially impacts on the inter-annual
variability and the trend derived over the period 1998–2008 both in
magnitude and in sign throughout the troposphere. Also, a tropical case is
discussed using the MOZAIC profiles taken over Windhoek, Namibia between 2005
and 2008. For this site, we found that the sampling uncertainty in the free
troposphere is around 8 and 12% at 12 and 4 profiles a month respectively. |
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