Impact of COVID-19-Related Air Traffic Reductions on the Coverage and Radiative Effects of Linear Persistent Contrails Over Conterminous United States and Surrounding Oceanic Routes

The radiative effects of the large-scale air traffic slowdown during April and May 2020 due to the international response to the COVID-19 pandemic are estimated by comparing the coverage (CC), optical properties, and radiative forcing of persistent linear contrails over the conterminous United States and two surrounding oceanic air corridors during the slowdown period and a similar baseline period during 2018 and 2019 when air traffic was unrestricted. The detected CC during the slowdown period decreased by an area-averaged mean of 41% for the three analysis boxes. The retrieved contrail optical properties were mostly similar for both periods. Total shortwave contrail radiative forcings (CRFs) during the slowdown were 34% and 42% smaller for Terra and Aqua, respectively. The corresponding differences for longwave CRF were 33% for Terra and 40% for Aqua. To account for the impact of any changes in the atmospheric environment between baseline and slowdown periods on detected CC amounts, the contrail formation potential (CFP) was computed from reanalysis data. In addition, a filtered CFP (fCFP) was also developed to account for factors that may affect contrail formation and visibility of persistent contrails in satellite imagery. The CFP and fCFP were combined with air traffic data to create empirical models that estimated CC during the baseline and slowdown periods and were compared to the detected CC. The models confirm that decreases in CC and radiative forcing during the slowdown period were mostly due to the reduction in air traffic, and partly due to environmental changes.

Automated summary

The radiative effects of the air traffic slowdown during the COVID-19 pandemic were estimated by comparing the contrails over the United States and surrounding air corridors during the slowdown and a baseline period. The detected coverage and optical properties of contrails did not show significant differences between the two periods, but the radiative forcing was 34% to 42% smaller during the slowdown. Empirical models considering the changes in atmospheric environment and air traffic confirmed that the reduction in air traffic was the main factor contributing to the decrease in contrails and radiative forcing.