and Muvva V. Ramana
of the Center for Clouds, Chemistry and Climate, Scripps Institution of Oceanography, UCSD , La Jolla, California 92037, USA along with their colleagues in the NASA Langley Research Center, Hampton, Virginia 23681-0001, USA has proposed that warming trends in Asia have been amplified by brown cloud solar absorption.
Atmospheric brown clouds are mostly the result of biomass burning and fossil fuel consumption. They consist of a mixture of light-absorbing and light-scattering aerosols and therefore contribute to atmospheric solar heating and surface cooling.
The authors used three lightweight unmanned aerial vehicles that were vertically stacked between 0.5 and 3 km over the polluted Indian Ocean. Over a three-week period during March 2006, the scientists took measurements of soot, sulphate and nitrate levels and solar radiation over the Maldive Islands in the Indian Ocean. These unmanned aerial vehicles deployed miniaturized instruments measuring aerosol concentrations, soot amount and solar fluxes.
During 18 flight missions the three unmanned aerial vehicles were flown with a horizontal separation of tens of metres or less and a temporal separation of less than ten seconds, which made it possible to measure the atmospheric solar heating rates directly.
The authors found that atmospheric brown clouds enhanced lower atmospheric solar heating by about 50 per cent. Our general circulation model simulations, which take into account the recently observed widespread occurrence of vertically extended atmospheric brown clouds over the Indian Ocean and Asia, suggest that atmospheric brown clouds contribute as much as the recent increase in anthropogenic greenhouse gases to regional lower atmospheric warming trends.
The combined warming trend of 0.25 K per decade may be sufficient to account for the observed retreat of the Himalayan glaciers
