Contrail detection at nighttime combining lidar, meteorological and system ADS-B data

Cloud formation, especially cirrus type, is affected also by the human activities such is aviation, which emits condensation trails, called contrails. Contrails form and persist under specific environmental conditions. Their formation is conditioned by the fulfillment of the Schmidt–Appleman, and later on their persistence is guaranteed over the ice supersaturated regions. These conditions, use the air temperature and relative humidity related to water and ice as criteria for their formation and persistence. These criteria depend, not only on the meteorological conditions but also on the aircraft specification, their fuel type, engine efficiency, etc.

One interesting topic of the contrail effects is the investigation of their contribution on the formation of the cirrus clouds. The formation of the cirrus clouds requires generally significantly higher relative humidity then the contrail persistence conditions. In this way, the investigation of the persistent contrails with relative humidity lower than cirrus clouds need to be formed, enable to have insight over the contribution of the contrails on the cirrus formation.

Currently, we have a 20-year database that allows us to do statistics but at night, which requires us to develop methods for differentiating clouds and contrails. Lidar backscattering profiles are collocated with system ADS-B data of the flight overpassing the Observatory of Haute-Provence in France. Detailed information about the flight routes and meteorological conditions, associated with the contrail properties have been analyzed statistically and case by case.

Here, statistics of the contrail formation and persistence conditions over the site is presented. The events have been classified into five cases; persistent, non-persistent, potential, uncertain and no contrails. The geometrical and optical properties of the contrails, as well as related meteorological variables provided by ERA5, are grouped according to this classification. The principal factor analyses on the contrail parameters is performed and their outputs have been clustered to identify better the main features of the most important parameters.

In addition to these statistics, some special cases of the contrail events have been analysed. The information provided by system  ADS-B collocated with the lidar vertical-resolved profiles identify and follow up the evolution of the contrails over the site. Their mean altitude, geometrical thickness, spatial orientation, timespan, width, optical depth and their persistency have been analysed in thoroughly. To have adequate determination and discrimination of the contrail spots, sensitivity analyses have been performed for the backscattering ratio, and their spatial and temporal distances between their neighbors. In short, complementary analyses, using statistics and cases studies, is performed to clarify the features of the contrail main properties.