Monday, 13 May 2002: 1:15 PM
Spreading of isolated contrails during the 2001 air traffic shutdown
Fractional cirrus cloud cover over the United States grew by 0.010/decade between 1971 and 1996, while the cirrus coverage over areas with minimal air traffic declined by 0.017/decade. The increase over the USA is highly correlated with the density of air traffic. While it is possible to estimate the cirrus coverage resulting from young linear contrails with 1-km infrared satellite data, it is difficult to determine the full impact of contrails because they often spread into non-linear, natural-looking cirrus clouds. Determination of the contribution of these spreading contrails requires the use of 4-km resolution geostationary satellite infrared data to track the contrails as they develop. Estimation of the contribution of individual contrails to the cirrus coverage is exacerbated by the low resolution of the satellite imagery that precludes the detection of new contrails or natural cirrus clouds forming in the same air mass. Often, as the air mass advects, new contrails, especially in high traffic areas over the USA, overlay the spreading contrails. During the September 2001 air traffic shutdown, conditions over the Midwestern USA were primed for contrail formation. However, only a few aircraft transited the clear supersaturated air mass resulting in several isolated spreading contrails in a an area normally crossed by 70-80 planes per hour. This paper presents a case study of the growth of these individual contrails using a combination of half-hourly Geostationary Operational Environmental Satellite (GOES-8), Moderate Resolution Imaging Spectroradiometer (MODIS), and Advanced Very High Resolution Radiometer (AVHRR) data. The areal coverage, microphysical properties, and the radiative effects of these contrails are computed for each image available during the lifetimes of these contrails. The results are correlated with the vertical profiles of temperature, humidity, and wind speed and direction relative to the flight path. The findings of this study will be extremely valuable for gaining a better understanding of the impact of spreading contrails on the increase of cirrus clouds over the USA.