Investigating contrails within cirrus clouds

<p>Effects of aviation on the Earth’s radiation budget and climate related to CO<sub>2</sub> emissions and from the formation of linear contrails and contrail cirrus have been the focus of detailed studies. Aviation effects on existing cirrus clouds are much less investigated. Contrail formation in existing cirrus clouds has the potential to increase the cloud optical thickness (COT) of optically thin cirrus, which might result in a net cooling effect.</p><p>Spaceborne remote sensing generally provides the means for studying the impact of aviation on climate. However, only active instruments such as lidar or radar can be used to study the effect of contrails that form within existing cirrus clouds. For such an investigation, the location of an aircraft at a given time needs to be matched with information on cloud coverage, cloud type, cloud layer height, and COT as can be retrieved from spaceborne CALIPSO lidar data.</p><p>We have developed an algorithm to find intersections of aircraft flight tracks with satellite tracks. Besides the spatial coordinates, the time difference between the passing of the aircraft and the satellite at the intersection is monitored and relevant aircraft data and satellite recordings are retrieved at the intersection. The algorithm is highly adjustable so that it can be adapted for other applications such as investigation of ship tracks or cloud tracking. The new algorithm has been used to identify aircraft flying through cirrus clouds in remote regions of the Earth to study the effects of individual aircraft on existing cirrus.</p>