Aircraft-generated contrails and their resulting cirrus clouds may exacerbate climate warming in those areas characterized by frequent commercial flights. For the United States, the majority of persisting contrails occur as clusters, or "outbreaks", which can persist over relatively large regions (i.e. U.S. Midwest) for many hours. In particular, contrail outbreaks occurring in otherwise mostly clear skies significantly modify radiation and energy budgets, and help reduce the range of temperature in the lower atmosphere between day and night. Their study would allow for evaluating human influences on climatic factors. Recently, some airline companies and foreign governments have expressed a desire to reduce aviation impacts on the environment and climate, including those related to contrails. Realization of this goal requires both a fuller understanding of the space and time-scale characteristics of outbreaks, and an ability to forecast their occurrence in a timely manner, thus potentially permitting horizontal or vertical diversion of high-altitude flights around such areas. This research will determine the geographical and meteorological space and time scales of clear-sky contrail outbreaks through analysis of high resolution satellite imagery with data from composites of key meteorological variables near aircraft cruising altitudes stratified by season and by U.S. sub-regions. These analyses will form the basis for predictive (statistical) models of outbreaks with an eye towards their eventual use in operational forecasting. Geographic Information Systems will be used for both statistical model development---using conventional meteorological data, satellite cloud and moisture retrievals, and aviation data---and for validation of outbreak events conducted on independent data and time periods. Advanced geostatistical techniques will be applied to the imagery containing the outbreaks to simulate their removal and estimate resulting impacts on the radiation and energy budgets and surface temperature. The research also will further clarify the impacts of contrails on Earth surface temperatures and will demonstrate the potential value of implementing the models by focusing on an optimal subset of outbreaks for case study investigation.
