Changes in cirrus cloud properties and occurrence over Europe during the COVID-19-caused air traffic reduction

. By inducing linear contrails and contrail cirrus, air traffic has a main impact on the ice cloud coverage and occurrence. During the COVID-19 pandemic, civil air traffic over Europe was significantly reduced, in March and April 2020, to about 80 % compared to the year before. This unique situation allows us to study the effect of air traffic on cirrus clouds. This work investigates, based on satellite lidar measurements, if and how cirrus cloud properties and occurrence changed over Europe in the course of COVID-19. Cirrus cloud properties are analyzed for different years between 2014 and 2019, which showed similar teorological conditions for the month of April as in 2020