Operational Meteorology in West Africa: Observational Networks, Weather Analysis and Forecasting A
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Operational meteorology in West Africa: observational networks, weather analysis and forecasting A. H. Fink, A. Agustí-Panareda, D. J. Parker, J.-P. Lafore, J.-B. Ngamini, E. Afiesimama, A. Beljaars, Olivier Bock, M. Christoph, F. Didé, etal. To cite this version: A. H. Fink, A. Agustí-Panareda, D. J. Parker, J.-P. Lafore, J.-B. Ngamini, et al.. Operational meteo- rology in West Africa: observational networks, weather analysis and forecasting. Atmospheric Science Letters, Wiley, 2011, 12 (1), pp.135-141. 10.1002/asl.324. hal-00572981 HAL Id: hal-00572981 https://hal.archives-ouvertes.fr/hal-00572981 Submitted on 10 Jan 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution - NonCommercial| 4.0 International License ATMOSPHERIC SCIENCE LETTERS Atmos. Sci. Let. 12: 135–141 (2011) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/asl.324 Operational meteorology in West Africa: observational networks, weather analysis and forecasting Andreas H. Fink,1* Anna Agust´ı-Panareda,2 Douglas J. Parker,3 Jean-Philippe Lafore,4 Jean-Blaise Ngamini,5 Ernest Afiesimama,6 Anton Beljaars,2 Olivier Bock,7 Michael Christoph,1 Francis Dide,´ 8 Claudia Faccani,4 Nadia Fourrie,´ 4 Fatima Karbou,4 Jan Polcher,9 Zilore Mumba,10 Mathieu Nuret,4 Susan Pohle,1 Florence Rabier,4 Adrian M. Tompkins11 and George Wilson12 1Institute of Geophysics and Meteorology, University of Cologne, Cologne, Germany 2ECMWF, Reading, UK 3School of Earth and Environment, University of Leeds, UK 4CNRM-GAME, Met´ eo-France´ & CNRS, Toulouse, France 5ASECNA, Dakar, Senegal 6NIMET, Abuja, Nigeria 7IGN/LAREG and IPSL/LATMOS, Paris, France 8DMN Benin,´ Cotonou, Benin´ 9LMD/IPSL/CNRS, Paris, France 10ACMAD, Niamey, Niger 11ICTP, Trieste, Italy 12GMA, Accra, Ghana *Correspondence to: Abstract Andreas H. Fink, Institute of Geophysics and Meteorology, Real-time surface and upper-air observations are crucial to the analysis and forecast- University of Cologne, Kerpener ing of the West African monsoon (WAM). This paper will focus on the African Mon- Str. 13, D-50923 soon – Multidisciplinary Analyses (AMMA)-driven reactivation and modernisation of the Cologne, Germany. radiosonde network over West Africa, its potential long-term impact on upper-air opera- E-mail: fi[email protected] tions in the region, the influence of the additional data in WAM analyses and forecasting, and the AMMA-related development and usage of the West African Analysis/Forecasting (WASA/F) forecast method. Copyright 2011 Royal Meteorological Society Received: 9 February 2010 Revised: 1 November 2010 Keywords: West Africa; radiosonde network; weather analysis; forecasting Accepted: 11 December 2010 1. Introduction in situ wind, temperature, pressure, and humidity data at a high vertical resolution, permit the best possible Real-time, in situ, and remote surface and upper-air definition of the (thermo-)dynamic state of the tropo- observations are crucial to the analysis and forecasting sphere, especially at lower levels. The determination of the West African monsoon (WAM). Beyond these of the state of the atmosphere in the lowest few kilo- benefits in day-to-day weather forecasting, an obser- metres in the WAM region is of pivotal importance vational network, well-maintained over many years, since it is the low-level vertical profiles of tempera- allows for the compilation of high-quality (re-)analysis ture, humidity and wind that favour or disfavour the data sets, thereby supporting process, climate, and organisation of West African rainy systems and that are model validation studies. Despite the advent of many crucial for determining the influx of moisture from the satellite sensors in the last four decades, whose data surrounding oceans. are assimilated in operational analyses, surface sta- Operational and maintenance costs of radiosonde tion data and upper-air information from radiosondes networks are, however, very high and the (West) remained an essential source of information over land African radiosonde network has been degrading over for weather forecast models mainly for the following many years before the African Monsoon – reasons (Tompkins et al., 2005; Faccani et al., 2009; Multidisciplinary Analyses (AMMA) programme was Agust´ı-Panareda et al., 2010a): (1) usage of satellite launched in 2002 (cf Parker et al., 2008). The com- data is still predominantly limited to cloud-free pix- plete lack of operating radiosonde stations in the ◦ els; (2) satellites provide indirect information with a important monsoon inflow zone south of 10 N, relatively coarse vertical resolution; and (3) a hith- upstream of the African Easterly Jet (AEJ) east of erto very limited use of satellite channels with peak 10 ◦E, and in the northern Sahel between 15 ◦N and sensitivity in the lower troposphere, due to the het- 20 ◦N (Figure 1) was identified as a major risk to erogeneous surface emissivity. As a consequence, the successful achievement of AMMA scientific goals present-day radiosonde systems that provide digital (Polcher et al., 2011). Beyond the support of AMMA’s Copyright 2011 Royal Meteorological Society 136 A. H. Fink et al. 30 30°N 51 122 62 30 62 28 50 61 31 30 ° 31 28 25 N 300 62 123 61 0 61 1 61 60 20°N 0 24 183 31 0 44 ° 80 26 58 0 19 15 N 44 0 179 49 62 63 0 46 46 50 23 0 10°N 1 174 171 158 23 0 0 0 33 0 178 79 0 5°N 0 8 0 27 0 1 4 0 3 1 0° 0 3 56 28 0 5°S 30°W1020°W °W0° 10°E200 °E30°E40°E Figure 1. Number of soundings received on the GTS in August 2006 from stations and synoptic times representative of the 2005 (pre-AMMA) operational radiosonde network (numbers in italics) and AMMA Special Observing Period soundings in August 2006 (numbers in boldface). scientific goals, the AMMA-funded refurbishment and AMMA, forecasters often lacked a modern concep- enhancement of the radiosonde network pursued two tual framework for analysing and forecasting the major further aims: (1) to support local agencies in updat- synoptic features of the WAM. Thus, another focus ing/refurbishing existing stations, establishing new sta- of the present contribution will be the description tions, and training their staff; and (2) to evaluate the of the West African Synthetic Analysis/Forecasting optimal network for Numerical Weather Prediction (WASA/F) method developed within AMMA. (NWP) and climate monitoring by, for example, per- In Section 2, the successes, failures, and potential forming Observing System Experiments (OSEs). The long-term operational impacts of the refurbished West achievements of AMMA in terms of the latter two African radiosonde network is discussed. Section 3 is goals are one focus of the present paper. dedicated to the impact of the additional data on WAM While the operation and exploitation of radiosonde analyses and forecasting. In Section 4, the principal and part of surface data for aviation purposes in the approach of WASA/F is introduced and Section 5 West African francophone countries (except Guinea) provides a conclusion. is managed by Agence pour la Securit´ e´ de la Naviga- tion Aerienne´ en Afrique et a` Madagascar (ASECNA), the National Weather Services (NWS) run the sur- 2. The AMMA radiosonde campaign: face meteorological networks and are responsible for successes, problems, and long-term issuing weather forecasts at the national level. This operational impacts unique organisational structure is one of the many reasons for the large diversity in financial and tech- The dilapidated state of the West African radiosonde nical facilities across West African analysis and fore- network before AMMA and the multi-faceted chal- casting centres. A typical use of upper-air data has lenges faced to refurbish, re-activate, and to establish been the manual streamline analyses at metric height new upper-air stations has been described in detail levels (e.g. 600, 900, 1500, and 2100 m). Combined in Parker et al. (2008). Some salient successes of the with surface wind and dewpoint-based analyses of AMMA campaign were the – at least temporary – re- the Intertropical Discontinuity (ITD) location, these activation of long-silent stations [e.g. Tamale (Ghana, charts formed the basis for nowcasting at ASECNA inactive since 1981), Abidjan (Ivory Coast, silent and NWS centres until very recently. This situa- since 2001), Ngaoundere (Cameroon, almost no data tion was improved at many NWS headquarters by feeding into the Global Telecommunication System, the European Organisation for the Exploitation of GTS), Conakry (Guinea), and Tessalit (Mali, became Meteorological Satellites (EUMETSAT)-funded instal- active in 2007 and 2008)], as well as the establish- lation of Preparation for Use of MSG in Africa ment of three new stations in the coastal inflow zone, (PUMA) satellite receiving stations. At the African viz. Cotonou and Parakou (both Benin) and Abuja Centre of Meteorological Application for Develop- (Nigeria). The enhanced station network operational ment (ACMAD) (Niger) another source of weather in August 2006 is evident from Figure 1. For the charts was through the Met´ eo-France´ Forecasting 2 years 2006 and 2007, a unique spatial and temporal Synergie System fed by the Reseau de Transmis- density of highly resolved (vertically every 5–10 m) sion d’Information Met´ eorologique´ (RETIM)-Afrique sounding data are available for the WAM region. transmission link. However, before the arrival of Between 2005 and 2009, some 13,500 high-resolution Copyright 2011 Royal Meteorological Society Atmos.