Assessment of a global contrail modeling method and operational strategies for contrail mitigation
Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics.
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Recent updates to the IPCC estimates of radiative forcing contributions from aircraft have raised concerns about the impacts of contrails and aviation-induced cirrus on climate. Increasing demand for aviation will further increase contrail formation. This thesis provides a model to assess operational options for reducing contrail coverage. This model couples realistic flight performance and best-available global meteorological data assimilations. Comparisons were made between satellite-identified contrails and contrail persistence estimates from flight data for 53,844 U.S. continental flights performed during the week of November 11/12-18, 2001. The satellite data were processed by NASA Langley Research Center using methods for identifying contrails as described by Mannstein . Given detailed knowledge of the aircraft types and radar-based trajectory data, simulated contrails did not match contrails observed in the satellite images. First, striated cirrus cloud formations were misidentified as contrail pixels. This resulted in the "contrails" typically aligning N-S, while most aircraft routes are aligned E-W. Perhaps 40-50% of the contrail pixels were misidentified. Second, a total of 60-90% of the contrail pixels (all demonstrated to be either contrails or clouds) occurred in areas where the assimilated meteorological fields showed RHi < 100%. This demonstrates that the RHi fields, although representative, do not accurately portray the true RHi fields on a given day in 2001. Finally, the typical length of the estimated contrails (several degrees) was longer than the typical length of the observed contrails (one degree).(cont.) This may reflect a limitation of the satellite sensing of the contrails, but it also implies that the chord lengths used within aviation system model need to be shortened so that they are consistent with length-scales observed in the RHi data. Despite the inability to replicate satellite data, the model was used to develop preliminary estimates of the costs and benefits of operational strategies for contrail and aviation-induced cirrus mitigation. Custom reroutes which minimized fuel burn were created reflecting different options for flying above, below, and around regions of high relative humidity. These options were all consistent with standard reroute procedures employed by the airlines and the Federal Aviation Administration. Using these custom reroutes, analyses were completed for 581 continental flights between 14 city pairs, and 628 international flights over the North Atlantic between 15 city pairs. Given perfect knowledge of meteorological data and no air traffic controls, if aircraft were individually rerouted, it was possible to mitigate 65%-80% of persistent contrails and simultaneously achieve an average decrease of 5%-7% of the total operating cost for the week in November 2001 for which this analysis was carried out. These reductions are relative to the actual routes flown by the aircraft during this week, reflecting the impact of non-optimal routing not only on contrail formation, but also on fuel bum and operating costs in general. Significant contrail reduction may also be achieved if aircraft are rerouted in weekly increments. For the time period that was analyzed it was possible to mitigate 40%-75% of persistent contrails for a change of -10% to +5% of the total operating cost.(cont.) An assessment was also made of the cost for mitigating contrails compared to the custom reroute that minimized fuel bum. In this case, 55%-85% of the contrails could be mitigated, for roughly a 0.5-1% increase in time and 2.5-3.5% increase in fuel bum (or 1-2% increase in total operating cost). In general, contrail persistence can be mitigated by altering latitude/longitude trajectory, flying at an altitude much lower or much higher than the tropopause, flying a route that minimizes fuel bum, and choosing more northerly routes over the Atlantic Ocean. Key areas of uncertainty that may impact these results include the validity of the contrail identification methods, the validity/range/resolution of the RHi estimates obtained from the assimilated meteorological data, the advection of contrails over time, the chord lengths in the aviation system model, the value of RHi assumed as the contrail persistence threshold, the validity of the engine modeling methods, the database of flights examined, and the construction of the custom reroutes. Further, contrail formation is a strong function of latitude and time of year. Therefore, the results cannot be generalized beyond the global regions and times of year that were analyzed.
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005.Includes bibliographical references (p. 170-173).
DepartmentMassachusetts Institute of Technology. Dept. of Aeronautics and Astronautics.
Massachusetts Institute of Technology
Aeronautics and Astronautics.