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| Titel |
A new Dobson Umkehr ozone profile retrieval method optimising information content and resolution |
| VerfasserIn |
K. Stone, M. B. Tully, S. K. Rhodes, R. Schofield |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 3 ; Nr. 8, no. 3 (2015-03-04), S.1043-1053 |
| Datensatznummer |
250116199
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| Publikation (Nr.) |
 copernicus.org/amt-8-1043-2015.pdf |
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| Zusammenfassung |
The standard Dobson Umkehr methodology to retrieve coarse-resolution ozone profiles used by the
National Oceanographic and Atmospheric Administration uses designated solar zenith angles
(SZAs). However, some information may be lost if measurements lie outside the designated SZA range
(between 60° and 90°), or do not conform to the fitting technique. Also, while
Umkehr measurements can be taken using multiple wavelength pairs (A, C and D), past retrieval
methods have focused on a single pair (C). Here we present an Umkehr inversion method that uses
measurements at all SZAs (termed operational) and all wavelength pairs. (Although, we caution direct comparison to
other algorithms.)
Information content for a Melbourne, Australia (38° S, 145° E) Umkehr
measurement case study from 28 January 1994, with SZA range similar to that designated in previous
algorithms is shown. When comparing the typical single wavelength pair with designated SZAs to the
operational measurements, the total degrees of freedom (independent pieces of information) increases from
3.1 to 3.4, with the majority of the information gain originating from Umkehr layers 2 + 3 and
4 (10–20 km and 25–30 km respectively). In addition to this, using all available wavelength
pairs increases the total degrees of freedom to 5.2, with the most significant increases in Umkehr
layers 2 + 3 to 7 and 9+ (10–40 and 45–80 km). Investigating a case from 13
April 1970 where the measurements extend beyond the 90° SZA range gives further
information gain, with total degrees of freedom extending to 6.5. Similar increases are
seen in the information content. Comparing the retrieved Melbourne Umkehr time series with
ozonesondes shows excellent agreement in layers 2 + 3 and 4 (10–20 and 25–30 km) for
both C and A + C + D-pairs. Retrievals in layers 5 and 6 (25–30 and 30–35 km) consistently show
lower ozone partial column compared to ozonesondes. This is likely due to stray light effects
that are not accounted for in the forward model, and under represented stratospheric aerosol. |
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