Forecasting for a Lagrangian aircraft campaign

[摘要] A forecast system has been developed in preparation for an upcoming aircraftmeasurement campaign, where the same air parcels polluted by emissions overNorth America shall be sampled repeatedly as they leave the continent, duringtransport over the Atlantic, and upon their arrival over Europe. This paperdescribes the model system in advance of the campaign, in order to make theflight planners familiar with the novel model output. The aim of a Lagrangianstrategy is to infer changes in the chemical composition and aerosoldistribution occurring en route by measured upwind/downwind differences.However, guiding aircraft repeatedly into the same polluted air parcelsrequires careful forecasting, for which no suitable model system exists todate. This paper describes a procedure using both Eulerian-type (i.e.concentration fields) and Lagrangian-type (i.e. trajectories) model outputfrom the Lagrangian particle dispersion model FLEXPART to predict the bestopportunities for a Lagrangian experiment. The best opportunities are definedas being highly polluted air parcels which receive little or no emissioninput after the first measurement, which experience relatively little mixing,and which are reachable by as many aircraft as possible. For validation thesystem was applied to the period of the NARE 97 campaign where approximatelythe same air masses were sampled on different flights. Measuredupwind/downwind differences in carbon monoxide (CO) and ozone (O₃)decreased significantly as the threshold values used for accepting cases asLagrangian were tightened. This proves that the model system can successfullyidentify Lagrangian opportunities.

[学科分类] 大气科学