Aerosol Characterization and Radiative Forcing Assessment Using Satellite Data and Models
M. Chin/L. Remer
October 26, 2012 15:26:07
Description of Problem
Aerosols affect the Earth’s energy budget directly by scattering and absorbing radiation and indirectly by acting as cloud condensation nuclei and, thereby, affecting cloud properties. Aerosols can be transported thousands of miles downwind, thereby having important implications for climate change and air quality on a wide range of scales. Enhanced new satellite passive sensors introduced in the last decade, the emerging measurements of aerosol vertical distributions from space-borne lidars provided the opportunity to attempt measurement-based characterization of aerosol and assessment of aerosol radiative forcing. Such satellite-based methods can play a role in extending temporal and spatial scale of field campaigns and evaluating and constraining model simulations. On the other hand, model simulations and measurements from field campaigns can provide essential parameters that satellites don’t observe. The overall goal of this research is to characterize aerosol distributions and assess the aerosol radiative forcing through an integration of multiple satellite observations and model simulations.
Scientific Objectives and Approach
During the past year, we conducted three major tasks: (1) we examined seasonal variations of the three-dimensional distribution of aerosols on a global scale through a statistical analysis of CALIPSO lidar observations, GOCART model, and MODIS aerosol optical depth (AOD) observations; (2) we estimated climate impacts of aerosol intercontinental transport based on 9 aerosol models that conduct a series of numerical experiments of reducing anthropogenic emissions by 20% respectively in four major industrial regions (North America, Europe, East Asia, and South Asia) under the Hemispheric Transport of Air Pollution (HTAP) framework. Specifically, we calculated the relative annual intercontinental response (RAIR), defined as the percentage contribution of long-range transport of foreign emissions relative to a sum of foreign and domestic emissions in a specific region; and (3) we examined relationships between fine-mode AOD and carbon monoxide (CO) on different temporal and spatial scales from both MODIS 7-year measurements and GOCART model simulations to understand emissions, chemistry, and transport in determining the distributions of aerosols and CO.
The CALIPSO-GOCART-MODIS analysis [Yu et al., 2010] shows that the CALIPSO observations of geographical patterns and seasonal variations of AOD are generally consistent with GOCART simulations and MODIS retrievals especially near source regions, while the magnitude of AOD shows large discrepancies in most regions. Both the CALIPSO observation and GOCART model show that the aerosol extinction scale heights in major dust and smoke source regions are generally higher than that in industrial pollution source regions. The CALIPSO aerosol lidar ratio also generally agrees with GOCART model within 30% on regional scales. Major differences between satellite observations and GOCART model are identified, including (1) an underestimate of aerosol extinction by GOCART over the Indian sub‐continent, (2) much larger aerosol extinction calculated by GOCART than observed by CALIPSO in dust source regions, (3) much weaker in magnitude and more concentrated aerosol in the lower atmosphere in CALIPSO observation than GOCART model over transported areas in mid-latitudes, and (4) consistently lower aerosol scale height by CALIPSO observation than GOCART model.
The HTAP analysis has contributed to Chapter A5: Impacts on Health, Ecosystems, and Climate [HTAP 2010 Assessment Report, in press]. It shows that for all regions and species, import from long-range transport is significant, with RAIR ranging from 9 to 30%. South Asia is most influenced by import of sulfate aerosol, and North America is most influenced by import of black carbon (BC), followed by particulate organic matter (POM). For sulfate, POM, and BC combined, South Asia RF is most strongly influenced by foreign sources, and North America and Europe is the least. Interestingly, RAIR values for AOD and RF of sulfate are much smaller than that for aerosol column loading. This probably stems from transported sulfate aerosols experiencing lower relative humidity at high altitude (resulting in lower AOD) than local aerosols, which generally remain at lower altitudes. The large model variability highlights the significant uncertainties in modeling aerosol processes.
The aerosol and CO analysis [Bian et al., 2010] shows that temporal correlations between CO and fine-mode AOD differ substantially over different timescales and different regions. On daily to synoptic scales CO and fine-mode AOD have a positive correlation over the industrial and biomass burning source regions owing to the covariance of emissions and coherent dynamic transport. No such correlation is seen in remote regions because of the diverging influence of mixing and chemical processes during long‐range transport. On the seasonal scale in the Northern Hemisphere, CO and fine-mode AOD are out of phase by 2–4 months, which is caused by photochemical production of sulfate and photochemical destruction of CO, together with the seasonality of fine‐mode dust. In the Southern Hemisphere tropics and subtropics, however, CO and fine-mode AOD are generally in‐phase because the variability is dominated by direct release from biomass burning emissions.
Refereed Journal Publications
Yu, H., M. Chin, D.M. Winker, A. Omar, Z. Liu, C. Kittaka, and T. Diehl, Global view of aerosol vertical distributions from CALIPSO lidar measurements and GOCART simulations: Regional and seasonal variations, J. Geophys. Res., 115, D00H30, doi:10.1029/2009JD013364, 2010.
Bian, H., M. Chin, R. Kawa, H. Yu, T. Diehl, and T. Kucsera Multi-scale carbon monoxide and aerosol correlations from satellite measurements and GOCART model: implication for emissions and atmospheric evolution, J. Geophys. Res., 115, D07302, doi:10.1029/2009JD012781, 2010.
Other Publications and Conferences
Yu, H., M. Chin, Impact of aerosol long-range transport on the direct radiative forcing of climate as derived from HTAP model simulations, EGU General Assembly, Vienna, Austria, May 2-7, 2010.
Yu, H., M. Chin, Q. Tan, L.A. Remer, Y. Zhang, O. Kalashnikova, R.A. Kahn, S. Peyridieu, A. Chédin, Climatology of trans-Atlantic dust transport derived from multiple satellite measurements and a global model, The A-Train Symposium, New Orleans, Louisiana, October 25-28, 2010.
Yu, H., Y. Zhang, Y. Yang, L.A. Remer, and M. Chin, An integrated analysis of above-cloud aerosols from A-Train Measurements: CALIOP AOD and OMI AI, The A-Train Symposium, New Orleans, Louisiana, October 25-28, 2010.