Atmospheric composition of West Africa: highlights from the AMMA program

The atmospheric composition of West Africa reflects the interaction of various dynamical and chemical systems (i.e. biogenic, urban, convective and long-range transport) with signatures from local to continental scales. Recent measurements performed during the African Monsoon Multidisciplinary Analyses (AMMA) observational periods in 2005 and 2006 provide new data which has allowed new insight into the processes within these systems that control the distribution of ozone and its precursors. Using these new data and recently published results, we provide an overview of these systems with a particular emphasis on ozone distributions over West Africa during the wet season.

'Your secret language': classics in the British colonies of West Africa

What were the cultural politics of classics in British colonies? Did classical education operate as a sign of oppression, or as a tool for forging an anti-colonial politics? Why did Europeans bring the classics to West Africa, and how did they manage the developing dynamic when West Africans laid independent claim to the classical heritage? This ground-breaking study examines the ways in which European colonisers and West African nationalists clashed, or collaborated, over the uses of Latin, Greek and the classics.

Creating a greater partnership: analysing partnership in the Catholic Church development chain

This paper presents results from a project designed to explore the meaning and function of partnership within the Catholic Church development chain. The geography literature has had little to say about such aid chains, especially those founded on faith-based groups. The relationships between three Catholic Church-based donors - referred to as A, B and C - with development personnel of the diocese of the Abuja Ecclesiastical Province (AEP) as well as other Catholic Church structures in Nigeria were analysed. The aim was to explore the forces behind the relationships and how 'patchy' these relationships were in AEP. Respondents were asked to give each of the donors a score in relation to four questions covering their relationship with the donors. Results suggest that the modus operandi of donor 'A' allows it to be perceived as the 'best' partner, while 'B' was scored less favourably because of a perception that it attempts to act independently of existing structures in Nigeria rather than work through them. There was significant variation between diocese in this regard, as well as between the diocese and other structures of the Church (Provinces, Inter-Provinces and National Secretariat). Thus 'partnership' in the Catholic Church aid chain is a highly complex, contested and 'visioned' term and the development of an analytical framework has to take account of these fundamentals.

'They Shall Speak the Arabic Language and Take Pride in it': reconsidering the fate of Coptic after the Arab Conquest

The complaints on the adoption of Arabic by the Copts that are voiced by the Apocalypse of Pseudo-Samuel have often been quoted as the expiring words of the dying Coptic language. This article seeks to show that they are not to be taken so literally, and that they should rather be inserted in the context of a rift within the medieval Coptic church over the question of language choice, and beyond this, over that of accommodation with the Muslims. The use of Arabic by the episcopal church of Miṣr and by some prominent figures around it, which was linked to their proximity to the Fatimid court, was resented and denounced by more traditional circles, centred on the Patriarchate and on some important monasteries such as the one at Qalamūn where the Apocalypse was written. The suggestion is also made that the text is contemporary with the beginning of Coptic literary production in Arabic and with the introduction of Egyptian Christians at the caliphal court, namely in the last quarter of the tenth century, at the time of Severus ibn al-Muqqafa‘.

West African storm tracks and their relationship to Atlantic tropical cyclones

The automatic tracking technique used by Thorncroft and Hodges (2001) has been used to identify coherent vorticity structures at 850hPa over West Africa and the tropical Atlantic in the ECMWF 40-year reanalysis. The presence of two dominant source regions, north and south of 15ºN over West Africa, for storm tracks over the Atlantic was confirmed. Results show that the southern storm track provides most of the storms that reach the main development region where most tropical cyclones develop. There exists marked seasonal variability in location and intensity of the storms leaving the West African coast, which may influence the likelihood of downstream intensification and longevity. There exists considerable year-to-year variability in the number of West African storm tracks, both in numbers over the land and continuing out over the tropical Atlantic Ocean. While the low-frequency variability is well correlated with Atlantic tropical cyclone activity, West African rainfall and SSTs, the interannual variability is found to be uncorrelated with these. In contrast, variance of the 2-6-day-filtered meridional wind, which provides a synoptic-scale measure of African Easterly Wave activity, shows a significant, positive correlation with tropical cyclone activity at interannual timescales.

Cross-hemispheric transport of Central African biomass burning pollutants: Implications for downwind ozone production

Pollutant plumes with enhanced concentrations of trace gases and aerosols were observed over the southern coast of West Africa during August 2006 as part of the AMMA wet season field campaign. Plumes were observed both in the mid and upper troposphere. In this study we examined the origin of these pollutant plumes, and their potential to photochemically produce ozone (O3) downwind over the Atlantic Ocean. Their possible contribution to the Atlantic O3 maximum is also discussed. Runs using the BOLAM mesoscale model including biomass burning carbon monoxide (CO) tracers were used to confirm an origin from central African biomass burning fires. The plumes measured in the mid troposphere (MT) had significantly higher pollutant concentrations over West Africa compared to the upper tropospheric (UT) plume. The mesoscale model reproduces these differences and the two different pathways for the plumes at different altitudes: transport to the north-east of the fire region, moist convective uplift and transport to West Africa for the upper tropospheric plume versus north-west transport over the Gulf of Guinea for the mid-tropospheric plume. Lower concentrations in the upper troposphere are mainly due to enhanced mixing during upward transport. Model simulations suggest that MT and UT plumes are 16 and 14 days old respectively when measured over West Africa. The ratio of tracer concentrations at 600 hPa and 250 hPa was estimated for 14–15 August in the region of the observed plumes and compares well with the same ratio derived from observed carbon dioxide (CO2) enhancements in both plumes. It is estimated that, for the period 1–15 August, the ratio of Biomass Burning (BB) tracer concentration transported in the UT to the ones transported in the MT is 0.6 over West Africa and the equatorial South Atlantic. Runs using a photochemical trajectory model, CiTTyCAT, initialized with the observations, were used to estimate in-situ net photochemical O3 production rates in these plumes during transport downwind of West Africa. The mid-troposphere plume spreads over altitude between 1.5 and 6 km over the Atlantic Ocean. Even though the plume was old, it was still very photochemically active (mean net O3 production rates over 10 days of 2.6 ppbv/day and up to 7 ppbv/day during the first days) above 3 km especially during the first few days of transport westward. It is also shown that the impact of high aerosol loads in the MT plume on photolysis rates serves to delay the peak in modelled O3 concentrations. These results suggest that a significant fraction of enhanced O3 in mid-troposphere over the Atlantic comes from BB sources during the summer monsoon period. According to simulated occurrence of such transport, BB may be the main source for O3 enhancement in the equatorial south Atlantic MT, at least in August 2006. The upper tropospheric plume was also still photochemically active, although mean net O3 production rates were slower (1.3 ppbv/day). The results suggest that, whilst the transport of BB pollutants to the UT is variable (as shown by the mesoscale model simulations), pollution from biomass burning can make an important contribution to additional photochemical production of O3 in addition to other important sources such as nitrogen oxides (NOx) from lightning.

The TAMORA algorithm: satellite rainfall estimates over West Africa using multi-spectral SEVIRI data

A multi-spectral rainfall estimation algorithm has been developed for the Sahel region of West Africa with the purpose of producing accumulated rainfall estimates for drought monitoring and food security. Radar data were used to calibrate multi-channel SEVIRI data from MSG, and a probability of rainfall at several different rain-rates was established for each combination of SEVIRI radiances. Radar calibrations from both Europe (the SatPrecip algorithm) and Niger (TAMORA algorithm) were used. 10 day estimates were accumulated from SatPrecip and TAMORA and compared with kriged gauge data and TAMSAT satellite rainfall estimates over West Africa. SatPrecip was found to produce large overestimates for the region, probably because of its non-local calibration. TAMORA was negatively biased for areas of West Africa with relatively high rainfall, but its skill was comparable to TAMSAT for the low-rainfall region climatologically similar to its calibration area around Niamey. These results confirm the high importance of local calibration for satellite-derived rainfall estimates. As TAMORA shows no improvement in skill over TAMSAT for dekadal estimates, the extra cloud-microphysical information provided by multi-spectral data may not be useful in determining rainfall accumulations at a ten day timescale. Work is ongoing to determine whether it shows improved accuracy at shorter timescales.