Contrails and Climate Change: The use of satellite thermal imagery to investigate aviation influences on the Irish climate.
Gillian M. Whelan1, Fiona Cawkwell1 Hermann Mannstein2, Patrick Minnis3
1 Geography Department,University College Cork; email@example.com 2DLR Institute of Atmospheric Physics 3NASA Langley Research Centre
Aircraft condensation-trails, or ‘contrails’, have been found to have a net warming effect on the climate system, with strong regional and seasonal dependence. In addition, when ambient atmospheric conditions are amenable; persistent contrails can induce additional cirrus-cloud formation as they spread, which can further impact climate. Due to Ireland’s position at the entrance to the North-Atlantic Flight Corridor, contrails and contrail-cirrus could be of particular relevance to our regional climate. Satellite imagery is the only source of data that allows objective production of a cloud and contrail climatology for the course of a whole year. Linear contrails are visible in 1km 11 & 12 µm AATSR and AVHRR satellite imagery, particularly in the temperature difference images between these two thermal channels. An automated Contrail Detection Algorithm (CDA) is applied to archived AATSR imagery over the Irish region to obtain a contrail climatology. Preliminary results from morning and evening AATSR overpasses during 2008 show a similar annual average contrail-coverage of 0.180% and 0.148% respectively, even though air-traffic density is typically ~9 times higher during the morning overpasses. Daytime contrail-coverage is highest during spring, corresponding to an overlap of increasing air-traffic moving into summer but more contrail-favourable meteorological conditions during winter and spring. Cases of excessive contrail-coverage, of up to 2.061% have been observed in combination with extensive cirrus coverage over Ireland. In conjunction with meteorological data, concurrent with satellite overpasses, the meteorological conditions for contrail formation and persistence are also analysed.
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