Radiosonde humidity bias correction over the West African region for the special AMMA reanalysis at ECMWF

A. Agusti-Panareda 1 D. Vasiljevic 1 A. Beljaars 1 O. Bock 2 F. Guichard 3 M. Nuret 3 A. Garcia Mendez 1 E. Andersson 1 P. Bechtold 1 A. Fink 4 H. Hersbach 1 J.-P. Lafore 3 J.-B. Ngamini 5 D. J. Parker 6 J.-L. Redelspergerc 3 A. M. Tompkins 7
1 ECMWF - European Centre for Medium-Range Weather Forecasts
2 LAREG - LAboratoire de Recherche en Géodésie [Champs-sur-Marne]
3 CNRM-GAME - Groupe d'étude de l'atmosphère météorologique
4 University of Cologne
5 ASECNA
6 University of Leeds
7 ICTP - Abdus Salam International Centre for Theoretical Physics [Trieste]
Abstract : During the African Monsoon Multidisciplinary Analysis (AMMA) field experiment in 2006 there was a large increase in the number of radiosonde data over West Africa. This has the potential of improving the numerical weather prediction (NWP) analysis/forecast and the water budget studies over that region. However, it is well known that the humidity from radiosondes can have some errors depending on sonde type, relative humidity (RH), temperature and the age of the sensor and can give rise to dry biases that are typically between 5% and 30% for RH. Three main sonde types were used in the AMMA field experiment: Vaisala RS80A, Vaisala RS92 and MODEM. In this article, a new empirical method is presented by using the operational European Centre for Medium-Range Weather Forecasts (ECMWF) short-range forecast as an intermediary dataset for computing biases. The validation of the correction method using global positioning system (GPS) total columnar water vapour (TCWV) confirms that the method is able to correct for a large part of the dry biases associated with the different sonde types. Results from analysis experiments show how the correction of humidity is particularly important in the West African region due to its impact on the development of convection in NWP models. The proposed radiosonde humidity bias correction has been applied to the special AMMA reanalysis experiment performed at ECMWF for the 2006 West African wet monsoon season. This is expected to benefit a wide number of AMMA-related studies that make use of the reanalysis, in particular those focusing on the water cycle. Copyright © 2009 Royal Meteorological Society
Mots-clés : erreur due à l'instrument mesure statistique AMMA radiosonde bias humidity observations data assimilation reanalysis campagne de mesures AMMA biais dans les mesures par radiosonde radiosondage observations d'humidité assimilation des données réanalyse moindres carrés séries de Fourier élévation solaire cycle hydrologique prévision numérique mousson
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Submitted on : Friday, May 15, 2009 - 7:09:26 PM
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A. Agusti-Panareda, D. Vasiljevic, A. Beljaars, O. Bock, F. Guichard, et al.. Radiosonde humidity bias correction over the West African region for the special AMMA reanalysis at ECMWF. Quarterly Journal of the Royal Meteorological Society, Wiley, 2009, 135 (595), pp.P. 595-617. ⟨10.1002/qj.396⟩. ⟨meteo-00384824⟩

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