Determining Smoke Particle Sphericity Using CATS Data

Determining Smoke Particle Sphericity Using CATS Data

Natalie Midzak¹, John E. Yorks², Edward Nowottnick³, Matthew J. McGill²

1. Millersville University, Millersville, PA (contact email: namidzak@millersville.edu)
2. NASA, Goddard Space Flight Center, Greenbelt, MD
3. GESTAR, Universities Space Research Association, Columbia, MD

Smoke from biomass burning in southern Africa prevails throughout the southern hemispheric winter months and has direct and indirect impacts on Earth’s radiation budget and region’s air quality. These smoke plumes are often detected in satellite remote sensing data over this region. The Cloud Aerosol Transport System (CATS), an elastic backscatter lidar located on the International Space Station (ISS), has been operational since February 2015 providing near real-time backscatter and depolarization measurements from the tropics and mid-latitudes. Data from CATS is used to study effects of clouds and aerosols on the Earth’s climate system and monitor dynamic events such as wildfires and biomass burning.

CATS regularly transects the African biomass burning region, providing depolarization ratio measurements of smoke particle sphericity. Additionally, MODIS active fire imagery provides information about the location of the fires, while HYSPLIT back trajectories trace the path of transport of various plumes. The biomes and burning materials of source regions reveal that smoke particle sphericity is heavily influenced by geographic factors and vegetation. In regions with burning of dry materials, non-spherical smoke particles dominate. However, burning of moist savannah vegetation results in spherical particles, which likely include tar-balls found in previous studies. In addition to case studies, depolarization ratios from a six-month burning period in 2015 (May - Oct.) provide evidence of significant amounts of non-spherical smoke particles. Models assume the shape of smoke to be spherical, however these results from CATS support previous observations of non-spherical smoke, especially in dry regions and transported plumes from high temperature fires. Finally, this study will help inform CATS aerosol typing algorithms, which based on prior assumptions of sphericity, misclassified depolarizing smoke layers as dust over regions of southern Africa.