Evaluation of balloon and satellite water vapour measurements in the Southern tropical and subtropical UTLS during the HIBISCUS campaignReportar como inadecuado

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1 SHTI - LATMOS LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales 2 LACy - Laboratoire de l-Atmosphère et des Cyclones 3 GSMA - Groupe de spectrométrie moléculaire et atmosphérique 4 Center for Atmospheric Science, University Chemical Laboratory 5 IUP - Institute of Environmental Physics Bremen 6 Équipe Stratosphère LACy - Laboratoire de l-Atmosphère et des Cyclones

Abstract : 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.

Autor: Nadège Montoux - Alain Hauchecorne - Jean-Pierre Pommereau - Franck Lefèvre - Georges Durry - R.L. Jones - Alexei Rozanov - San

Fuente: https://hal.archives-ouvertes.fr/


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