Aviation contrail cirrus and radiative forcing over Europe during 6 months of COVID-19

Abstract

The COVID-19 pandemic led to a 72% reduction of air traffic over Europe in March-August 2020 compared to 2019. Modelled contrail cover declined similarly, and computed mean instantaneous radiative contrail forcing dropped regionally by up to 0.7 W m-2. Here, model predictions of cirrus optical thickness and the top-of-the atmosphere outgoing longwave and reflected shortwave irradiances are tested by comparison to Meteosat-SEVIRI-derived data. The agreement between observations and modelled data is slightly better when modelled contrail cirrus contributions are included. The spatial distributions and diurnal cycles of the differences in these data between 2019 and 2020 are partially caused by differences in atmospheric and surface conditions, particularly for solar radiation in the spring of 2020. Aviation signals become discernible in the observed differences of these data between 2019 and 2020 when subtracting numerical weather prediction model results that approximate the atmosphere and surface conditions without contrails.