Evidence of impact of aviation on cirrus cloud formation

by C S Zerefos, K Eleftheratos, D S Balis, P Zanis, G Tselioudis, C Meleti
ATMOSPHERIC CHEMISTRY AND PHYSICS ()
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Abstract

This work examines changes in cirrus cloud cover (CCC) in possible\nassociation with aviation activities at congested air corridors. The\nanalysis is based on the latest version of the International Satellite\nCloud Climatology Project D2 data set and covers the period 1984-1998.\nOver the studied areas, the effect of large-scale modes of natural\nclimate variability such as ENSO, QBO and NAO as well as the possible\ninfluence of the tropopause variability, were first removed from the\ncloud data set in order to calculate long-term changes of observed\ncirrus cloudiness. The results show increasing trends in (CCC) between\n1984 and 1998 over the high air traffic corridors of North America,\nNorth Atlantic and Europe. Of these upward trends, only in the\nsummertime over the North Atlantic and only in the wintertime over North\nAmerica are statistically significant (exceeding +2.0% per decade).\nOver adjacent locations with low air traffic, the calculated trends are\nstatistically insignificant and in most cases negative both during\nwinter and summer in the regions studied. These negative trends, over\nlow air traffic regions, are consistent with the observed large scale\nnegative trends seen in (CCC) over most of the northern middle latitudes\nand over the tropics. Moreover, further investigation of vertical\nvelocities over high and low air traffic regions provide evidence that\nthe trends of opposite signs in (CCC) over these regions, do not seem to\nbe caused by different trends in dynamics. It is also shown that the\nlongitudinal distribution of decadal changes in (CCC) along the latitude\nbelt centered at the North Atlantic air corridor, parallels the spatial\ndistribution of fuel consumption from highflying air traffic, providing\nan independent test of possible impact of aviation on contrail cirrus\nformation. The correlation between the fuel consumption and the\nlongitudinal variability of (CCC) is significant (+0.7) over the middle\nlatitudes but not over the tropics. This could be explained by the fact\nthat over the tropics the variability of (CCC) is dominated by dynamics\nwhile at middle latitudes microphysics explain most of its variability.\nResults from this study are compared with other studies and for\ndifferent periods of records and it appears that there exists general\nagreement as to the evidence of a possible aviation effect on high cloud\npositive trends over regions with congested air traffic.

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