Surprisingly high absorption of solar radiation by forest fires

Smoke from forest and savanna fires in Africa absorbs much more solar radiation than was previously thought. This has become clear from analyses of smoke measurements above the clouds made by the SCIAMACHY satellite instrument and published in Geophysical Research Letters.

Measuring smoke above the clouds
Researchers from the Royal Netherlands Meteorological Institute (KNMI) and TU Delft have developed a new technique for measuring smoke above the clouds using satellites. In Africa, enormous quantities of smoke are released into the atmosphere during the dry monsoon season from June to November as a result of the many forest and savanna fires. When this smoke is carried by favourable air currents to the area above the south-eastern Atlantic Ocean, a remarkable amount of solar radiation is absorbed by the smoke particles above the clouds, amounting to about 15 per cent of the local incident sunlight. The absorbed solar radiation heats the air that is carrying the smoke.

New detection technique
This high absorption by smoke was unknown until recently because satellite observations of detecting smoke above the clouds were virtually impossible. Clouds reflect so much light that any smoke was too difficult to see. As the absorption of sunlight by smoke is particularly strong at very short wavelengths, a novel detection technique has been developed that makes use of all the wavelengths of sunlight reflected by the earth, which are measured by SCIAMACHY. Using this novel measuring technique, it is possible to distinguish between clouds and smoke.

Climate research
The research results are an important step forward in climate research. This enables the radiation process between clouds and smoke to be more effectively incorporated in climate models, enhancing the accuracy of this aspect of these models.

SCIAMACHY and Envisat
SCIAMACHY is a German-Dutch-Belgian satellite instrument on board the ESA’s Envisat satellite, which operated from 2002 to 2012. The successor to SCIAMACHY is TROPOMI, which will be launched in 2016.