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| Titel |
Evaluation of balloon and satellite water vapour measurements in the Southern tropical and subtropical UTLS during the HIBISCUS campaign |
| VerfasserIn |
N. Montoux, A. Hauchecorne, J.-P. Pommereau, F. Lefèvre, G. Durry, R. L. Jones, A. Rozanov, S. Dhomse, J. P. Burrows, B. Morel, H. Bencherif |
| 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 ; 9, no. 14 ; Nr. 9, no. 14 (2009-07-29), S.5299-5319 |
| Datensatznummer |
250007543
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| Publikation (Nr.) |
 copernicus.org/acp-9-5299-2009.pdf |
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| Zusammenfassung |
Balloon water vapour in situ and remote measurements in the tropical upper
troposphere and lower stratosphere (UTLS) obtained during the HIBISCUS
campaign around 20° S in Brazil in February–March 2004 using a tunable
diode laser (μSDLA), a surface acoustic wave (SAW) and a Vis-NIR solar
occultation spectrometer (SAOZ) on a long duration balloon, have been used
for evaluating the performances of satellite borne remote water vapour
instruments available at the same latitude and measurement period. In the
stratosphere, HALOE displays the best precision (2.5%), followed by SAGE
II (7%), MIPAS (10%), SAOZ (20–25%) and SCIAMACHY (35%), all of
which show approximately constant H2O mixing ratios between 20–25 km.
Compared to HALOE of ±10% accuracy between 0.1–100 hPa, SAGE II and
SAOZ show insignificant biases, MIPAS is wetter by 10% and SCIAMACHY
dryer by 20%. The currently available GOMOS profiles of 25% precision
show a positive vertical gradient in error for identified reasons. Compared
to these, the water vapour of the Reprobus Chemistry Transport Model, forced
at pressures higher than 95 hPa by the ECMWF analyses, is dryer by about
1 ppmv (20%).
In the lower stratosphere between 16–20 km, most notable features are the
steep degradation of MIPAS precision below 18 km, and the appearance of
biases between instruments far larger than their quoted total uncertainty.
HALOE and SAGE II (after spectral adjustment for reducing the bias with
HALOE at northern mid-latitudes) both show decreases of water vapour with a
minimum at the tropopause not seen by other instruments or the model,
possibly attributable to an increasing error in the HALOE altitude
registration. Between 16–18 km where the water vapour concentration shows
little horizontal variability, and where the μSDLA balloon measurements
are not perturbed by outgassing, the average mixing ratios reported by the
remote sensing instruments are substantially lower than the 4–5 ppmv
observed by the μSDLA. Differences between μSDLA and HALOE and
SAGE II (of the order of −2 ppmv), SCIAMACHY, MIPAS and GOMOS (−1 ppmv) and
SAOZ (−0.5 ppmv), exceed the 10% uncertainty of μSDLA, implying
larger systematic errors than estimated for the various instruments.
In the upper troposphere, where the water vapour concentration is highly
variable, AIRS v5 appears to be the most consistent within its 25%
uncertainty with balloon in-situ measurements as well as ECMWF. Most of the
remote measurements show less reliability in the upper troposphere, losing
sensitivity possibly because of absorption line saturation in their spectral
ranges (HALOE, SAGE II and SCIAMACHY), instrument noise exceeding 100%
(MIPAS) or imperfect refraction correction (GOMOS). An exception is the
SAOZ-balloon, employing smaller H2O absorption bands in the
troposphere. |
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