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  • Author or Editor: C. Robert Snider x
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Raymond A. Assel, C. Robert Snider, and Reginald Lawrence


Winter 1983 was one of the mildest winters in the past 200 years. One result of the unusual winter weather was the mildest overall ice season on the Great Lakes since systematic observations of ice cover extent on the Lakes were initiated some 20-odd years ago. The 1983 winter developed during the peak of one of the most intense El Niño-Southern Oscillation events of this century. Associated with the mild temperatures in the United States was an extremely strong Aleution low that persisted most of the winter. Monthly Northern Hemispheric circulation patterns were generally weak; no general long wave patterns were able to persist; and 700 mb heights were above normal. Annual maximum ice coverage on the Great Lakes was much below normal: Lake Superior 21% (normal is 75%), Lake Michigan 17% (normal is 45%), Lake Huron 36% (normal is 68%), Lake Erie 25% (normal is 90%), and Lake Ontario less than 10% (normal is 24%). Economic impact of the below-normal ice cover included reduced U.S. Coast Guard ice breaking assistance to commercial vessels, reduced U.S. Coast Guard flood relief operations in connecting channels of the Great Lakes, and virtually no ice-related winter power losses at hydropower plants on the St. Marys, Niagara and St. Lawrence Rivers.

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C. L. Reddington, K. S. Carslaw, P. Stier, N. Schutgens, H. Coe, D. Liu, J. Allan, J. Browse, K. J. Pringle, L. A. Lee, M. Yoshioka, J. S. Johnson, L. A. Regayre, D. V. Spracklen, G. W. Mann, A. Clarke, M. Hermann, S. Henning, H. Wex, T. B. Kristensen, W. R. Leaitch, U. Pöschl, D. Rose, M. O. Andreae, J. Schmale, Y. Kondo, N. Oshima, J. P. Schwarz, A. Nenes, B. Anderson, G. C. Roberts, J. R. Snider, C. Leck, P. K. Quinn, X. Chi, A. Ding, J. L. Jimenez, and Q. Zhang


The largest uncertainty in the historical radiative forcing of climate is caused by changes in aerosol particles due to anthropogenic activity. Sophisticated aerosol microphysics processes have been included in many climate models in an effort to reduce the uncertainty. However, the models are very challenging to evaluate and constrain because they require extensive in situ measurements of the particle size distribution, number concentration, and chemical composition that are not available from global satellite observations. The Global Aerosol Synthesis and Science Project (GASSP) aims to improve the robustness of global aerosol models by combining new methodologies for quantifying model uncertainty, to create an extensive global dataset of aerosol in situ microphysical and chemical measurements, and to develop new ways to assess the uncertainty associated with comparing sparse point measurements with low-resolution models. GASSP has assembled over 45,000 hours of measurements from ships and aircraft as well as data from over 350 ground stations. The measurements have been harmonized into a standardized format that is easily used by modelers and nonspecialist users. Available measurements are extensive, but they are biased to polluted regions of the Northern Hemisphere, leaving large pristine regions and many continental areas poorly sampled. The aerosol radiative forcing uncertainty can be reduced using a rigorous model–data synthesis approach. Nevertheless, our research highlights significant remaining challenges because of the difficulty of constraining many interwoven model uncertainties simultaneously. Although the physical realism of global aerosol models still needs to be improved, the uncertainty in aerosol radiative forcing will be reduced most effectively by systematically and rigorously constraining the models using extensive syntheses of measurements.

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