Mesospheric OH layer altitude at midlatitudes: variability over the Sierra Nevada Observatory in Granada, Spain (37° N, 3° W)
The mesospheric OH layer varies on several timescales, primarily driven by variations in atomic oxygen, temperature, density and transport (advection). Vibrationally excited OH airglow intensity, rotational temperature and altitude are closely interrelated and thus accompany each other through t...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-10-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/35/1151/2017/angeo-35-1151-2017.pdf |
| Summary: | The mesospheric OH layer varies on several timescales, primarily
driven by variations in atomic oxygen, temperature, density and transport
(advection). Vibrationally excited OH airglow intensity, rotational
temperature and altitude are closely interrelated and thus accompany each
other through these changes. A correct interpretation of the OH layer
variability from airglow measurements requires the study of the three
variables simultaneously. Ground-based instruments measure excited OH
intensities and temperatures with high temporal resolution, but they do not
generally observe altitude directly. Information on the layer height is
crucial in order to identify the sources of its variability and the causes
of discrepancies in measurements and models. We have used SABER
space-based 2002–2015 data to infer an empirical function for predicting
the altitude of the layer at midlatitudes from ground-based measurements of
OH intensity and rotational temperature. In the course of the analysis, we
found that the SABER altitude (weighted by the OH volume emission rate) at midlatitudes
decreases at a rate of 40 m decade<sup>−1</sup>, accompanying an increase of
0.7 % decade<sup>−1</sup> in OH intensity and a decrease of
0.6 K decade<sup>−1</sup> in OH equivalent temperature. SABER OH altitude barely
changes with the solar cycle, whereas OH intensity and temperature vary by
7.8 % per 100 s.f.u. and 3.9 K per 100 s.f.u., respectively. For
application of the empirical function to Sierra Nevada Observatory SATI data,
we have calculated OH intensity and temperature SATI-to-SABER transfer
functions, which point to relative instrumental drifts of
−1.3 % yr<sup>−1</sup> and 0.8 K yr<sup>−1</sup>, respectively, and a
temperature bias of 5.6 K. The SATI predicted altitude using the empirical
function shows significant short-term variability caused by overlapping
waves,
which often produce changes of more than 3–4 km in a few hours, going along
with 100 % and 40 K changes in intensity and temperature, respectively.
SATI OH layer wave effects are smallest in summer and largest around New
Year's Day. Moreover, those waves vary significantly from day to day. Our
estimations suggest that peak-to-peak OH nocturnal variability, mainly due to
wave variability, changes within 60 days at least 0.8 km for altitude in
autumn, 45 % for intensity in early winter and 6 K for temperature in
midwinter. Plausible upper limit ranges of those variabilities are
0.3–0.9 km, 40–55 % and 4–7 K, with the exact values depending on
the season. |
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| ISSN: | 0992-7689 1432-0576 |