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Earth science

African reflections

The outline of the geographical area shown here may be familiar, but the colouring won't be. This is north Africa and the Arabian peninsula, with the colours depicting the albedo of those parts of the region (almost all of it) that are arid and largely naked of vegetation. Albedo is a measure of the amount of solar radiation that is reflected back from a surface, into the atmosphere and space, and is therefore an essential parameter in climate modelling. Here, yellow corresponds to the highest albedos: the darker the shading, the lower the albedo (and the lower the amount of radiation reflected).

The albedo map comes from a paper by E. A. Tsvetsinskaya et al. (Geophys. Res. Lett. 29, 10.1029/2001GL014096; 2002), in which the authors relate albedo measurements of unprecedented spectral detail taken by the Moderate-resolution Imaging Spectroradiometer (MODIS), on the Terra spacecraft, to digitized maps of regional soil and rock types, at a 1-km spatial resolution. On the albedo image, the brightest parts correspond to areas of sand dunes; the darkest parts correspond to soil types known as vertisols, cambisols, rendzinas and luvisols, which occur mostly in and around the Atlas Mountains, and to volcanic and intrusive rocks.

The reason that the authors chose north Africa and the Arabian peninsula for study is in part because this huge desert belt is one of the most reflective areas on Earth. The energy gradient between this and adjacent areas, which absorb radiation strongly, can produce distinctive regional circulations in the atmosphere. The detailed analysis of albedo by spatial variation in the surface type should mean that this kind of data can more easily be accommodated in climate modelling.

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Lincoln, T. African reflections. Nature 417, 603 (2002). https://doi.org/10.1038/417603b

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