Contrails developed under frontal influences of the North Atlantic

摘要

Satellite imagery reveals a visually striking pattern of persistent line-shaped contrails located to the Northwest of the British Isles on 1 September 2007, just before sunrise. These contrails formed over the heavily trafficked eastbound North Atlantic Track (NAT) flight paths, as they intersected an area of prefrontal mixing. The high relative humidity with respect to ice within the prefrontal mixing zone allowed the contrails to persist, while the strictly regulated flight paths over the region account for their remarkable shapes. The positioning of the NAT flight paths to take advantage of the jet stream likely maximized regional contrail formation. An estimation of the outgoing top of the atmosphere longwave (LW) flux from the CERES instrument shows that the contrails reduced the local instantaneous LW emissivity by 20.96 (0.26) W/m ~2. This example demonstrates that for middle latitude regions, prefrontal mixing is an important factor governing the radiative influence of contrails. However, a full estimation of the radiative impact is not possible, as we cannot specify the amount of shortwave forcing caused by the persistence of the contrails into daytime; moreover, several hours after formation the line-shaped contrails spread and overlapped with pre-existing cloud structures.