The West African Plume

Seasonality: The anthropogenic West African plume exists from late December to early April each year and varies significantly inter annually.

Sources Anthropogenic: The anthropogenic WAP derives from: biomass burning linked to and clearing and agriculture; and gas flares in the oil production industry. Gas flares probably contribute more aerosols to this plume than to any other plume except possibly the Middle East Plume as Nigeria is reported to have flared 7.513 billion cubic metres of gas in 2016.

Sources Natural: One volcano, Mount Cameroon, is located in the region and the Global Volcanism Program lists nine eruptions since 1900 of maximum Volcanic Explosivity Index (VEI) 2. These eruptions are not considered significant in the global climate context because of the low number and low VEI.

Most Extreme: February 2016 was one of the most extreme apparition of the WAP in the Terra satellite data when it exhibited a maximum aerosol optical depth of 1.22 at its centre. The NASA image for this month is shown here.

Effects:  My paper presented at the AGU Fall Meeting in 2015 shows how the WAP causes drought in Spain in the boreal winter by perturbing the regional Hadley Cell. This effect is a mirror image of the effects of the SEAP which causes drought in the south east of south Australia by the same mechanism – the perturbation of the regional Hadley Cell. In addition my research indicates that the WAP has other effects on the winter climate of Europe and may have contributed to the drought in California.