Researchers at NASA are constantly browsing new satellite data and imagery delivered by the agency’s fleet of Earth-observing satellites for new data that may help answer questions about topics that are poorly understood or hotly debated within the scientific community.
While he was browsing new imagery captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite on May 9, 2016, NASA Goddard Space Flight Center atmospheric scientist Richard Kleidman found his attention immediately drawn toward the image above—a curling plume of smoke above a deck of clouds over Canada’s Northwest Territories. The smoke was likely lofted up by the destructive fire that burned in Alberta near Fort McMurray, though other fires in Saskatchewan and Manitoba may have contributed as well. “That is a fascinating image,” said Kleidman. “It is an excellent example of aerosol being transported above clouds—a topic currently of great interest to the aerosol research community.”
Aerosols are small airborne particles found in plumes of smoke, air pollution, dust, and volcanic ash. Scientists know that aerosols can affect the climate in critical ways, but some details about precisely how they do so remain up for debate. One of the key uncertainties relates to how aerosols interact with and affect clouds. And one of the drivers of that uncertainty stems from situations when aerosols end up above clouds.
A growing body of research suggests that the climate effects of dark-colored “absorbing” aerosols, which are common in smoke, differ markedly depending on whether the particles are found above clouds or in clear skies. When skies are clear, smoke generally leads to a cooling of the Earth-atmosphere system. When they are cloudy and smoke ends up above a cloud layer, the effect reverses; the same particles that would have had a cooling effect have a warming effect. The brighter the underlying cloud layer, the greater the warming effect, explained Hongbin Yu, an atmospheric scientist at Goddard.
Though several studies have demonstrated the effect of aerosols above clouds, few climate models currently incorporate it. This is partly because many current satellite-based datasets of aerosols exclude cloudy scenes because clouds make it difficult to measure aerosols accurately.
Despite this, scientists at Goddard and elsewhere are developing new strategies for monitoring aerosols above clouds. Hiren Jethva and Omar Torres, both at Goddard, have produced a global, decade-long record of aerosols above cloud using the Ozone Monitoring Instrument (OMI) on Aura. Kerry Meyer, also at Goddard, has developed an algorithm designed to measure aerosols above clouds with the Moderate Resolution Imaging Spectroradiometer (MODIS). Andrew Sayer, another scientist at Goddard, has begun work on a new algorithm that would make it possible to include absorbing aerosols above clouds in a key data record called Deep Blue. Meanwhile, a new five-year airborne field campaign based in Walvis Bay, Namibia, called ORACLES will begin collecting a suite of measurements, including of aerosols above clouds, over the southeastern Atlantic Ocean in 2016.
- Jethva, H. et al. (2016, May 5) A ten-year global record of absorbing aerosols above clouds from OMI’s near-UV observations. Proceedings SPIE, 41 (1), 186-192.
- Meyer, K.et al. (2015, June 3) Simultaneously inferring above-cloud absorbing aerosol optical thickness and underlying liquid phase cloud optical and microphysical properties using MODIS. Journal of Geophysical Research Atmospheres 120 (11), 5524-5547.
- NASA Aura Satellite Measurements of Aerosols Above Clouds. Accessed October 16, 2014.
- Sayer, A.et al.> (2016, May 7) Extending “Deep Blue” aerosol retrieval coverage to cases of absorbing aerosols above clouds: Sensitivity analysis and first case studies. Journal of Atmospheric Sciences.
- Torres, O.et al. (2012, March) Retrieval of Aerosol Optical Depth above Clouds from OMI Observations: Sensitivity Analysis and Case Studies. Journal of Atmospheric Sciences, 69 (3), 1037-1053.
- Yu, H. & Zhang, Z. (2013, June) New Directions: Emerging satellite observations of above-cloud aerosols and direct radiative forcing. Atmospheric Environment, 72, 36-40.
- Zhang, Z. em al (2016, February 11) Shortwave direct radiative effects of above-cloud aerosols over global oceans derived from 8 years of CALIOP and MODIS observations. Atmospheric Chemistry and Physics.
NASA Earth Observatory image by Jesse Allen, using data from the Land Atmosphere Near real-time Capability for EOS (LANCE). Caption by Adam Voiland, with input from Richard Kleidman, Andrew Sayer, and David Giles.
- Aqua - MODIS