Deep Convection over Africa: Annual Cycle, ENSO, and Trends in the Hotspots

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 widespread across Africa? Where on the continent is deep convection most active? Where does widespread 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 whereas 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 widespread 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 increased ~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.

Reductions in NO 2 burden over north equatorial Africa from decline in biomass burning in spite of growing fossil fuel use, 2005 to 2017

“…S12). Convective activity is low during November through February in north equatorial Africa and trends in annual convection in the region are small, especially in comparison with other parts of Africa (54). Systematic changes in Air Mass Factors (AMFs) over time could conceivably result in apparent VCD trends, but the OMI Standard Product (SP) version 3 AMFs do not exhibit clear, spatially consistent trends (SI Appendix, Fig.…”

Contrasting controls on Congo Basin evaporation at the two rainfall peaks

“…4c, 5a) and this may be due to the influence of mesoscale convective systems, which develop in the afternoon in November and block incoming sunlight. This hotspot of convective activity is not present in March (Jackson et al 2009;Hart et al 2019).…”

“…The lower LAI alone explains lower transpiration, and therefore lower evaporation, in November than March. LAI and transpiration are much lower in November than March at 2°S, 28°E, and this reflects the influence of mesoscale convective systems that develop in the afternoon in November but not in March (Jackson et al 2009, Hart et al 2019. These storms block DSR and strongly suppress LAI, transpiration, and evaporation.…”

Synoptic timescale linkage between midlatitude winter troughs Sahara temperature patterns and northern Congo rainfall: A building block of regional climate variability

“…25-6.25 N, 18.75-28.75 E. Blue: low-level temperature indices, with band N1-N5 covering ERA5 grid-boxes centred 9.75-15 N (indices referred to as approximately 10-15 N in the text). For analyses here, two adjacent boxes are averaged into one index, so N34 measures temperature to the north of NEC and N34 minus S34 measures the broad-scale Sahel-to-Equator temperature gradient operating over the longitudes of NEC [Colour figure can be viewed at wileyonlinelibrary.com] 1982-2016 and 2001-2016 are useful to compare, especially since the latter avoids a tendency for increased convection in some tropical areas after 1999 (e.g., Hart et al, 2019), and in particular in February over NC (T18). However, most anchor indices used do not contain this change (see Figures S1, S2, S3), such that the targeted synoptic features emerge naturally from the analyses without need for detrending and are mostly consistent over sub-periods within 1982-2016.…”