Influence of weather conditions on the distribution of persistent contrails

An automated contrail detection algorithm has been applied to AVHRR data to obtain the position of contrails. Nearly simultaneous data from the Europe Model of the Deutscher Wetterdienst have been used to find typical weather conditions associated with 742 persistent contrails. Further, a flow, patt ern analysis identifies typical regions where the occurrence of contrails w as above average. These regions are in the upper atmosphere: (a) ahead of a surface warm front either in moist warm layers before the cirrus clouds ar rive or more likely with the cirrus in a warm conveyor belt and (b) ahead o f a surface cold front in rapidly moving cold nir in the turbulent regions near a band of strong wind (though the speed is not necessarily as high as in a jet). Usually, the atmosphere is baroclinic in the contrail region. Mo st of the detected contrails occur in divergent flow, patterns in the tippe r troposphere in slowly rising warm or locally turbulent cold dir masses.