20. May 2020
Satellite data and atmospheric models show

Up to 90 per­cent few­er con­den­sa­tion trails due to re­duced air traf­fic over Eu­rope

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Aeronautics
Comparison of condensation trail coverage on 16 April 2020 for different air traffic conditions (contrails graphically highlighted)
Com­par­i­son of con­den­sa­tion trail cov­er­age on 16 April 2020 for dif­fer­ent air traf­fic con­di­tions (con­trails graph­i­cal­ly high­light­ed)
Image 1/4, Credit: DLR/EUROCONTROL/ECMWF

Comparison of condensation trail coverage on 16 April 2020 for different air traffic conditions (contrails graphically highlighted)

The im­ages com­pare the mod­elled op­ti­cal thick­ness of cir­rus clouds and con­den­sa­tion trails for weath­er con­di­tions and air traf­fic on 16 April 2020 at 12:00 CET (top) with the mod­elled cov­er­age that the sig­nif­i­cant­ly high­er air traf­fic of 16 April 2019 would have caused un­der the same weath­er con­di­tions (bot­tom). With­out re­stric­tions on air traf­fic, around 10 times as many con­trails would have formed in the re­gion shown over Cen­tral Eu­rope on 16 April 2020. Weight­ed with the op­ti­cal thick­ness­es, the de­gree of cov­er­age of the par­tial­ly over­lap­ping con­trails would be four times greater. The op­ti­cal thick­ness­es of the ice clouds were sim­u­lat­ed with the con­trail and cir­rus mod­el Co­CiP. The con­den­sa­tion trails are graph­i­cal­ly high­light­ed.
Comparison of condensation trail coverage on 16 April 2020 for different air traffic conditions (contrails graphically highlighted)
Com­par­i­son of con­den­sa­tion trail cov­er­age on 16 April 2020 for dif­fer­ent air traf­fic con­di­tions (with­out con­trails high­light­ed)
Image 2/4, Credit: DLR/EUROCONTROL/ECMWF

Comparison of condensation trail coverage on 16 April 2020 for different air traffic conditions (without contrails highlighted)

The im­ages com­pare the mod­elled op­ti­cal thick­ness of cir­rus clouds and con­den­sa­tion trails for weath­er con­di­tions and air traf­fic on 16 April 2020 at 12:00 CET (top) with the mod­elled cov­er­age that the sig­nif­i­cant­ly high­er air traf­fic of 16 April 2019 would have caused un­der the same weath­er con­di­tions (bot­tom). With­out re­stric­tions on air traf­fic, around ten times as many con­trails would have formed in the re­gion shown over Cen­tral Eu­rope on 16 April 2020. Weight­ed with the op­ti­cal thick­ness­es, the de­gree of cov­er­age of the par­tial­ly over­lap­ping con­trails would be four times greater. The op­ti­cal thick­ness­es of the ice clouds were sim­u­lat­ed with the con­trail and cir­rus mod­el Co­CiP. The con­den­sa­tion trails are graph­i­cal­ly high­light­ed.
Meteosat-11 satellite data compared with a model for the optical thickness of ice clouds
Me­teosat-11 satel­lite da­ta com­pared with a mod­el for the op­ti­cal thick­ness of ice clouds
Image 3/4, Credit: DLR/EUROCONTROL/ECMWF/EUMETSAT

Meteosat-11 satellite data compared with a model for the optical thickness of ice clouds

The im­ages show the op­ti­cal thick­ness of ice clouds de­rived from Me­teosat-11 satel­lite da­ta for weath­er and air traf­fic on 16 April 2020, 12:00 CET (top) com­pared to the mod­elled op­ti­cal thick­ness of cir­rus clouds and con­trails for weath­er and air traf­fic at the same time. Satel­lite ob­ser­va­tion and mod­el cal­cu­la­tions agree. The op­ti­cal thick­ness­es of the ice clouds were sim­u­lat­ed with the con­trail and cir­rus mod­el Co­CiP.
Condensation trails in the sky
Con­den­sa­tion trails in the sky
Image 4/4, Credit: DLR (CC-BY 3.0)

Condensation trails in the sky

Air­craft en­gines emit soot par­ti­cles. These act as con­den­sa­tion nu­clei for small, su­per­cooled wa­ter droplets, which im­me­di­ate­ly freeze in­to ice crys­tals and be­come vis­i­ble in the sky as con­den­sa­tion trails.
  • DLR has analysed the influence of reduced air traffic on contrails
  • Air traffic over Europe was compared between 16 April 2020 and 16 April 2019
  • Over the next few months, scientists will determine more precisely how the reduced contrail coverage will affect Earth's radiation budget in 2020
  • Focus: Aeronautics, space, climate change

Travel restrictions put in place to stem the COVID-19 pandemic have led to a massive decline in global air traffic since mid-March 2020. The European air traffic control authority, EUROCONTROL has reported that the volume of European air traffic in April 2020 declined by almost 90 percent compared to the beginning of the previous month. Researchers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) have now analysed the impact of reduced air traffic on the formation of condensation trails over Europe by measuring cloud properties. They used data acquired on 16 April 2020 by the ‘Spinning Enhanced Visible and Infrared Imager' (SEVIRI) sensor on a Meteosat Second Generation (MSG) weather satellite for this purpose. On that day, the atmosphere over Europe was cold and humid enough for long-lasting condensation trails to form behind aircraft. The analyses show a decrease in the number of contrails formed to about one tenth, compared to normal operations.

"Observations of the now-reduced condensation trail coverage allow us to verify the accuracy of the data analyses afforded by MSG weather satellites and the models that we use, so that we can determine the climate impact of condensation trails in greater detail in future," explains Christiane Voigt of the DLR Institute of Atmospheric Physics in Oberpfaffenhofen. "Since, in addition to carbon dioxide emissions, condensation trails are responsible for approximately half of the climate impact of air transport, we would expect that so little air traffic would result in a marked decrease in the climate impact." Regular global air traffic has hitherto been responsible for approximately five percent of global warming.

Ninety percent less air traffic over Europe
Ninety percent less air traffic over Europe
An almost 90 percent reduction in fuel consumption by air traffic in the upper airspace over Europe on 16 April 2020 (top) compared to the same time last year (bottom), calculated from EUROCONTROL data.

Credit: EUROCONTROL/DLR

The researchers compared the satellite measurements with a model developed at the DLR Institute of Atmospheric Physics, which calculates the coverage made up of natural clouds and cirrus clouds produced by aircraft contrails, based on current air traffic movements and weather data. Luca Bugliaro and Ulrich Schumann from the DLR Institute of Atmospheric Physics explain: "The findings based on the satellite imagery were largely consistent with the model data, and the model reflects the regional structures and gives a good representation of the measured values of the optical thicknesses of clouds." In addition, the scientists used the model to calculate a scenario with an air traffic volume 10 times higher, as it would have been on the same day in 2019, with the meteorological conditions kept the same in order to pinpoint the effect of traffic levels alone. The calculations clearly show far greater coverage from contrail cirrus clouds, with an increased optical thickness of the ice clouds. Weighted with the optical thicknesses, the degree of coverage of the partially overlapping contrails would be four times greater.

Over the coming months, scientists want to determine more precisely how the reduced coverage due to contrails and the related cirrus clouds will affect Earth's radiation budget, using more satellite data and analyses. To do this, measures include comparing the thermal radiation emitted by Earth, measured from space, with the incident solar radiation. "In this special situation, when there is very little air traffic, we hope to be able to directly demonstrate the effect of the decrease in condensation trails on Earth's heat balance through a large number of measurements," explains Markus Rapp, Director of the DLR Institute of Atmospheric Physics.

Ice clouds and condensation trails
Ice clouds and condensation trails
Thin ice clouds are shown as a white and pale grey pattern towards the top of the images, which illustrates radiation temperatures. Condensation trails are also visible here – white stripes indicate thick but still-young contrails. Older contrails overlap with one another and other clouds and are no longer visible as streaks. The upper image shows radiation temperature differences from the 10.8 and 12 micrometre channels of the Meteosat Second Generation (MSG) weather satellite, using the SEVIRI sensor, at 10:00 UTC on 16 April 2020. The lower image shows a false colour composite image of visible and infrared measurement data from the MSG/SEVIRI instrument for the same meteorological conditions.
Credit: EUMETSAT/DLR

Tiny ice crystals in cold air

Condensation trails consist largely of tiny ice crystals that form in cold air (at temperatures below approximately minus 42 degrees Celsius) from the exhaust gases of aircraft. First, water vapour condenses on soot particles in the exhaust gases, forming tiny water droplets. As they mix with the air, the droplets quickly cool and freeze to form ice crystals. If the surrounding air is sufficiently damp (oversaturated with ice), the ice crystals absorb water from their environment, grow, spread out and take on cloud-like shapes, which wrap around Earth like a scarf.

These contrail cirrus clouds keep some of the Earth's heat radiation within the atmosphere and thus have a warming effect on the climate. However, as they also reflect sunlight, they have a cooling effect at times. At present, the degree to which contrail cirrus clouds contribute towards the overall radiative forcing by air traffic is of a similar magnitude to the effect of carbon dioxide, which has been emitted by aircraft since the very beginning of aviation. Unlike carbon dioxide, which has a lifetime of over 100 years within the atmosphere, contrails usually dissipate within a matter of minutes or hours, so their climate impact is rapidly reduced if there is a decrease in air traffic. DLR is also investigating how contrails can be avoided by routing flights around areas of humid air.

Changes to the chemical composition of the atmosphere due to reduced air traffic are also to be researched during an upcoming aircraft mission with the Falcon and HALO research aircraft.

Contact
  • Falk Dambowsky
    Ed­i­tor
    Ger­man Aerospace Cen­ter (DLR)
    Me­dia Re­la­tions
    Telephone: +49 2203 601-3959
    Fax: +49 2203 601-3249
    Linder Höhe
    51147 Cologne
    Contact
  • Prof. Dr. Christiane Voigt
    Head of De­part­ment
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of At­mo­spher­ic Physics
    Cloud Physics
    Telephone: +49 8153 28-2579
    Fax: +49 8153 28-1841
    Münchener Straße 20
    82234 Oberpfaffenhofen
    Contact
  • Prof. Dr. Ulrich Schumann
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of At­mo­spher­ic Physics
    Telephone: +49 8153 28-2584
    Münchener Straße 20
    82234 Oberpfaffenhofen
    Contact
  • Dr. rer. nat. Luca Bugliaro
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of At­mo­spher­ic Physics
    Cloud Physics
    Telephone: +49 8153 28-2582
    Münchener Straße 20
    82234 Oberpfaffenhofen
    Contact
  • Prof. Dr. Markus Rapp
    Di­rec­tor
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of At­mo­spher­ic Physics
    Telephone: +49 8153 28-2521
    Fax: +49 8153 28-1841
    Münchener Straße 20
    82234 Oberpfaffenhofen
    Contact
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