Preprints
https://doi.org/10.5194/acp-2021-172
https://doi.org/10.5194/acp-2021-172

  09 Mar 2021

09 Mar 2021

Review status: this preprint is currently under review for the journal ACP.

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

Qiang Li and Silke Groß Qiang Li and Silke Groß
  • Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, D-82234 Oberpfaffenhofen, Germany

Abstract. 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 the 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 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, which showed similar meteorological conditions for March and April as they were found for 2020. Comparing these years shows that the cirrus cloud occurrence was reduced by about 30 % with smaller cloud thicknesses found in April 2020. The average thickness of cirrus clouds was reduced to 1.18 km in April 2020 compared to a value of 1.40 km under normal conditions. In addition, the cirrus clouds measured in April 2020 possess smaller mean values of the particle linear depolarization ratio (PLDR) than the previous years at high significance level, especially at colder temperatures (T < −50 °C). The same exercises are extended to the observations over the United States of America and over China. Besides the regional discrimination of cirrus clouds, we reach the final summary that cirrus clouds show significant changes of depolarization ratios in both March and April over Europe, no changes in both months over China, and significant changes only in April over USA.

Qiang Li and Silke Groß

Status: open (until 04 May 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-172', Anonymous Referee #1, 13 Apr 2021 reply
  • RC2: 'Comment on acp-2021-172', Anonymous Referee #2, 19 Apr 2021 reply

Qiang Li and Silke Groß

Qiang Li and Silke Groß

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Short summary
Aircrafts emit exhaust gases and particles directly into the atmosphere which may contribute to climate change. In this work, we present a significant reduction in the occurrence rate and particle linear depolarization ratio of cirrus cloud based on the analysis of lidar measurements with the CALIPSO satellite during COVID-19 when air traffic was significantly reduced. The findings imply that these clouds had formed in air with less influence by aviation.
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