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| Titel |
OH-equivalent temperatures derived from ACE-FTS and SABER temperature profiles – a comparison with OH*(3-1) temperatures from Maynooth (53.2° N, 6.4° W) |
| VerfasserIn |
F. J. Mulligan, R. P. Lowe |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 26, no. 4 ; Nr. 26, no. 4 (2008-05-13), S.795-811 |
| Datensatznummer |
250016062
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| Publikation (Nr.) |
 copernicus.org/angeo-26-795-2008.pdf |
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| Zusammenfassung |
OH-equivalent temperatures were derived from all of the temperature profiles
retrieved in 2004 and 2005 by the ACE-FTS instrument in a 5 degree band of
latitude centred on a ground-based observing station at Maynooth. A globally
averaged OH volume emission rate (VER) profile obtained from WINDII data was
employed as a weighting function to compute the equivalent temperatures. The
annual cycle of temperature thus produced was compared with the annual cycle
of temperatures recorded at the ground-based station more than a decade
earlier from the OH*(3-1) Meinel band. Both data sets showed excellent
agreement in the absolute value of the temperature minimum (~162 K)
and in its time of occurrence in the annual cycle at summer solstice. Away
from mid-summer, however, the temperatures diverged and reach a maximum
disagreement of more than 20 K in mid-winter. Comparison of the Maynooth
ground-based data with the corresponding results from two nearby stations in
the same time-period indicated that the Maynooth data are consistent with
other ground stations. The temperature difference between the satellite and
ground-based datasets in winter was reduced to 14–15 K by lowering the peak
altitude of the weighting function to 84 km. An unrealistically low peak
altitude would be required, however, to bring temperatures derived from the
satellite into agreement with the ground-based data.
OH equivalent temperatures derived from the SABER instrument using the same
weighting function produced results that agreed well with ACE-FTS. When the
OH 1.6 μm VER profile measured by SABER was used as the weighting
function, the OH equivalent temperatures increased in winter as expected but
the summer temperatures were reduced resulting in an approximately constant
offset of 8.6±0.8 K between ground and satellite values with the
ground values higher. Variability in both the altitude and width of the OH
layer within a discernable seasonal variation were responsible for the
changes introduced. The higher temperatures in winter were due to primarily
to the lower altitude of the OH layer, while the colder summer temperatures
were due to a thinner summer OH layer. We are not aware of previous reports
of the effect of the layer width on ground-based temperatures.
Comparison of OH-equivalent temperatures derived from ACE-FTS and SABER
temperature profiles with OH*(3-1) temperatures from Wuppertal at 51.3° N
which were measured during the same period showed a similar pattern to the
Maynooth data from a decade earlier, but the warm offset of the ground
values was lower at 4.5±0.5 K. This discrepancy between temperatures
derived from ground-based instruments recording hydroxyl spectra and
satellite borne instruments has been observed by other observers. Further
work will be required by both the satellite and ground-based communities to
identify the exact cause of this difference. |
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