Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 3 3 2003 10.5194/acpd-3-3335-2003 http://www.atmos-chem-phys-discuss.net/3/3335/2003/ http://www.atmos-chem-phys-discuss.net/3/3335/2003/acpd-3-3335-2003.html http://www.atmos-chem-phys-discuss.net/3/3335/2003/acpd-3-3335-2003.pdf 3335 3359 2003-06-30 Evidence of impact of aviation on cirrus cloud formation C. S. Zerefos K. Eleftheratos D. S. Balis P. Zanis G. Tselioudis C. Meleti Laboratory of Climatology & Atmospheric Environment, Faculty of Geology, National & Kapodistrian University of Athens, Greece Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, Greece Research Center for Atmospheric Physics & Climatology, Academy of Athens, Greece Goddard Institute for Space Studies, National Aeronautics and Space Administration, USA This work examines changes in cirrus cloud cover in possible association with aviation activities at congested air corridors. The analysis is based on the latest version of the International Satellite Cloud Climatology Project D2 data set and covers the period 1984&ndash1998. Over areas with heavy air traffic, the effect of large-scale modes of natural climate variability such as ENSO, QBO and NAO as well as the possible influence of the tropopause variability, were first removed from the cloud data set in order to calculate long-term changes of observed cirrus cloudiness. The results show increasing trends in cirrus cloud coverage, between 1984 and 1998, over the high air traffic corridors of North America, North Atlantic and Europe, which in the summertime only over the North Atlantic are statistically significant at the 99.5% confidence level (2.6% per decade). In wintertime however, statistically significant changes at the 95% confidence level are found over North America, amounting to +2.1% per decade. Statistically significant increases at the 95% confidence level are also found for the annual mean cirrus cloud coverage over the North Atlantic air corridor (1.2% per decade). Over adjacent locations with lower air traffic, the calculated trends are statistically insignificant and in most cases negative both during winter and summer in regions studied. Moreover, it is shown that the longitudinal distribution of decadal changes in cirrus cloudiness along the latitude belt centered at the North Atlantic air corridor, parallels the spatial distribution of fuel consumption from highflying air traffic, providing an independent test of possible impact of aviation on contrail cirrus formation. Results from this study are compared with other studies and different periods of records and it appears as evidenced in this and in earlier studies that there exists general agreement on the aviation effect on high cloud trends.