Satellite images of cloud cover help scientists understand African climate

Using over 30 years of satellite images, scientists studied how atmospheric air moves across the African continent. The information gained could help scientists better predict climate changes in Africa.

The study was based on the process of convection, which occurs when differences in temperature cause air to move through the atmosphere. In the type of convection known as deep convection, which this study focused on, air moves from the lower to the upper atmosphere, and these air movements are associated with changing weather and rainfall patterns.

Across Africa, convection has mostly been studied in specific regions and seasons, but there is very little information on how it occurs over the whole continent.

The researchers therefore looked at patterns of convection across the entire African continent to determine how the patterns change at different times of the year, and in different seasons.

They were especially interested in when convection is most widespread across Africa, how convection patterns have changed over the years, and the effects of special climate conditions like El Niño and La Niña. They also wanted to identify “hotspots”, or areas where a lot of convective activity occurs.

Using satellite images, the researchers studied cloud patterns across Africa from 1983 to 2015. This allowed them to determine where and when deep convection was occurring, and to observe what happened during years of special weather patterns known as “El Niño” and “La Niña”.

The researchers found that deep convective activity across Africa is most widespread in March, April and October.  As a result, during these months deep convection in Africa is likely to have a stronger effect on global climate. They also noted that, from December to February, a lot of convective activity occurs in eastern and southern African countries like Malawi, Tanzania and Mozambique, which could have effects on climate in, and beyond, Africa.

According to the researchers, convection patterns also change in El Niño years, which result in lower overall convective activity across Africa. In La Niña years, however, the activity increases. 

The researchers add that the biggest effects of these unusual weather years are seen in the hotspot identified across eastern and southern Africa, where a lot of variation in the amount of convective activity occurs as a result.

They also found that, overall, convective activity in Africa has increased by 10% over more than 30 years.

The study addresses a gap in scientific knowledge of overall convection patterns across Africa. Using these results, future researchers will have a clearer picture of the patterns of convection, and therefore climate, across the continent. This information can also be used to help scientists make more accurate models and predictions of African climate.

The researchers note that future work on these topics should examine the relationship between the convective hotspots found in this study, and African and global climate models.

Abstract

Africa is one of the three key regions of deep convection in the global tropics. There is a wealth of information on the intensity, variability and change of convection and associated rainfall in regions across the continent but almost all of this literature is regionally focused and confined to specific seasons. This fragmented approach precludes a continent-wide view of deep convection leaving the following key issues unanswered: When is deep convection the most wide-spread across Africa? Where on the continent is deep convection most active? Where does wide-spread convection have the most interannual variability? This paper confronts these questions using a satellite-derived integral of deep convection. At the continental scale, March exhibits the most extensive deep convection while the West African monsoon during June-July exhibits the least. El Niño generally suppresses pan-African convective activity while La Niña enhances this activity. These pan-African signals are largely determined by regional hotspots: the eastern Congo hosts the most persistent wide-spread deep convection, southeastern southern Africa displays the highest interannual variability, and regional highlands maintain local convective activity hotspots. Furthermore, pan-African annual mean convective activity has increase ∼10% between 1983 and 2015 with increases of >20% recorded in local hotspots. Results in this study provide a climatological baseline for both observational and model-based studies of African climates and offer insights into when African convection has the greatest potential impact on the general circulation.

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