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Ronald L. Drake, Patrick D. Coyle, and Daniel P. Anderson

Abstract

This paper is concerned with the effects of nonlinear eddy coefficients on rising, dry fine thermals. The base atmosphere in which these thermals are embedded is hydrostatic, horizontally homogeneous, nearly neutral, and without an ambient wind. By identifying the turbulent transfer terms with the subgrid–scale motions, a nonlinear formulation, based upon the worn. of Lilly and Smagorinsky, is obtained for the eddy coefficients. The mixing length in these terms is based upon a vorticity formulation rather than the size of the numerical grid used in the computations. Using numerical techniques based upon the work of Arakawa, and Adams and Bashforth, we tested these formulations by following the evolution of rising line thermals. We concluded that the eddy formulation used in this paper is more realistic than using constant coefficients throughout the field of computation. In addition, we found that the density stratification is important if the convective layer is deeper than 3 km.

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Ronald L. Drake, Patrick D. Coyle, and Daniel P. Anderson

Abstract

This paper is concerned with the time evolution of interactive dry line thermals in a convective layer. The temperature perturbations which produce these line thermals are randomly chosen. Since the domain of computation is the x-z plane, the evolving flow field is described by the streamfunction, vorticity, and the potential temperature. The nonlinear acceleration terms were differenced by an Arakawa scheme and the time differencing was the second-order, explicit, two-step Adams-Bashforth scheme. The turbulent transfer terms were given by a nonlinear formulation based on the work of Lilly and Smagorinsky. The convective layers in our numerical experiments were simulated by releasing a single set of thermals and by successive releases of thermals. Even though our work is a two-dimensional simulation, our results were consistent with the gross properties of real convective fields reported by several investigators. Hence, our system is a relatively inexpensive model that can be used to study convective layers over irregular surfaces and terrain.

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David M. Schultz, Altuğ Aksoy, Jeffrey Anderson, Tommaso Benacchio, Kristen L. Corbosiero, Matthew D. Eastin, Clark Evans, Jidong Gao, Almut Gassman, Joshua P. Hacker, Daniel Hodyss, Matthew R. Kumjian, Ron McTaggart-Cowan, Glen Romine, Paul Roundy, Angela Rowe, Elizabeth Satterfield, Russ S. Schumacher, Stan Trier, Christopher Weiss, Henry P. Huntington, and Gary M. Lackmann
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Guy P. Brasseur, Mohan Gupta, Bruce E. Anderson, Sathya Balasubramanian, Steven Barrett, David Duda, Gregg Fleming, Piers M. Forster, Jan Fuglestvedt, Andrew Gettelman, Rangasayi N. Halthore, S. Daniel Jacob, Mark Z. Jacobson, Arezoo Khodayari, Kuo-Nan Liou, Marianne T. Lund, Richard C. Miake-Lye, Patrick Minnis, Seth Olsen, Joyce E. Penner, Ronald Prinn, Ulrich Schumann, Henry B. Selkirk, Andrei Sokolov, Nadine Unger, Philip Wolfe, Hsi-Wu Wong, Donald W. Wuebbles, Bingqi Yi, Ping Yang, and Cheng Zhou

Abstract

Under the Federal Aviation Administration’s (FAA) Aviation Climate Change Research Initiative (ACCRI), non-CO2 climatic impacts of commercial aviation are assessed for current (2006) and for future (2050) baseline and mitigation scenarios. The effects of the non-CO2 aircraft emissions are examined using a number of advanced climate and atmospheric chemistry transport models. Radiative forcing (RF) estimates for individual forcing effects are provided as a range for comparison against those published in the literature. Preliminary results for selected RF components for 2050 scenarios indicate that a 2% increase in fuel efficiency and a decrease in NOx emissions due to advanced aircraft technologies and operational procedures, as well as the introduction of renewable alternative fuels, will significantly decrease future aviation climate impacts. In particular, the use of renewable fuels will further decrease RF associated with sulfate aerosol and black carbon. While this focused ACCRI program effort has yielded significant new knowledge, fundamental uncertainties remain in our understanding of aviation climate impacts. These include several chemical and physical processes associated with NOx–O3–CH4 interactions and the formation of aviation-produced contrails and the effects of aviation soot aerosols on cirrus clouds as well as on deriving a measure of change in temperature from RF for aviation non-CO2 climate impacts—an important metric that informs decision-making.

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