20080126 065716 Kahn Highlights Jan08

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All These Matter for Climate Studies with Satellite Aerosol Products: Sampling, Algorithm Assumptions about Surface & Aerosol Properties, Cloud Masking From: R. Kahn, M. Garay, et al., Satellite-derived Aerosol Optical Depth Over Dark Water from MISR and MODIS: Comparisons with AERONET and Implications for Climatological Studies, J. Geophys. Res., 2007 doi:10.1029/2006JD00175 Although the current MISR and MODIS satellite mid-visible aerosol optical thickness (AOT) products are accurate overall to about 0.05 or 20%, they differ systematically, on a global, monthly-average basis, by about 0.03 to 0.05. Some key climate change and other applications require accuracies of 0.03 or better. The instruments are sufficiently stable and well characterized, and have adequate signal-to-noise, to realize such precision. But assumptions made in the current Standard Aerosol Retrieval Algorithms produce AOT biases that must be addressed first. By analyzing coincident MISR, MODIS, and AERONET observations, we identify and quantify contributions to the discrepancies from: instrument calibration and sampling differences, assumptions made in the MISR and MODIS Standard algorithms about ocean surface boundary conditions, missing particle property or mixture options, and the way reflectances used in the retrievals are selected. Each contributes significantly to the observed differences under some circumstances. These results lead to specific algorithm upgrades, and point to ways to effectively use the currently available products for regional and global applications. Sampling differences at Ascension Island, 18 Feb. 2005: MISR, MODIS, and AERONET all view this clean maritime aerosol air mass, but there is a 60% change in AOT across the relative humidity boundary marked by clouds; AERONET sees the highest AOT and MODIS the lowest. Using any one of these AOT data sets to represent the entire region would lead to large errors, but taken together, they give a better picture.

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Wildfire Smoke, Dust & Volcanic Aerosol Plumes Form Near-surface, or in Stable Atmospheric Layers Aloft From: R. Kahn, et al., Aerosol source plume physical characteristics from space-based multiangle imaging, J. Geophys. Res. 2007, doi:10.1029/2006JD007647 Thin dust plumes lifted only by regional winds, or smoke from less-intense fires, remain near the surface. However, when sources have sufficient buoyancy, aerosol plumes concentrate in high-elevation, locally stable atmospheric layers; the aerosol is not uniformly distributed up to a peak altitude, as is sometimes assumed in numerical models. Multi-angle imaging from the MISR instrument, on the NASA Earth Observing System’s Terra satellite, determines the amount, type, horizontal extent, and vertical distribution of particles in aerosol source regions. These quantities, especially when combined with fire radiant energy flux and broader spatial coverage from the EOS MODIS instrument, provide information needed to more accurately model aerosol plume evolution, and to assess the impact of particle pollution on the environment. Oregon Wildfire Sept 04 2003 Orbit 19753 Blks 53-55 MISR Aerosols V17 MISR Stereo Plume Heights Progressing Downwind + NCEP Atmospheric Stability

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About 10% of 2004 Alaska Wildfires Injected Smoke Above the Atmospheric Boundary Layer From: R. Kahn, Y. Chen, D. Nelson, et al., Wildfire Smoke Injection Heights – Two Perspectives from Space, Geophys. Res. Lett., in press 2008 The elevation at which wildfire smoke is injected into the atmosphere has a strong influence on how far the smoke travels, and is a key input to aerosol transport models. Aerosol layer height is derived with great precision from space-borne lidar, but horizontal sampling is very poor on a global basis. Aerosol height derived from space-borne stereo imaging is limited to source plumes having discernable features. But coverage is vastly greater, and captures the cores of major fires, where buoyancy can be sufficient to lift smoke above the near-surface boundary layer. Assessment of smoke injection from the Alaska-Yukon region during summer 2004 finds at least about 10% of wildfire smoke plumes reached the free troposphere. Modeling of smoke environmental impacts can benefit from the combined strengths of the stereo and lidar observations.