Abstract
AbstractThe largest share in the climate impact of aviation results from contrail cirrus clouds. Here, the dependence of microphysical contrail ice properties and extinction on temperature and humidity is investigated. Contrail measurements were performed at various altitudes during the 2018 ECLIF II/NDMAX campaign with the NASA DC‐8 chasing the DLR A320. Ice number concentrations and contrail extinction coefficients are largest at altitudes near 9.5 km, typical for short‐ and medium‐range air traffic. At higher altitudes near 11.5 km, low ambient water vapor concentrations lead to smaller contrail particle sizes and lower extinction coefficients. In addition, contrails were detected below 8.2 km near the Schmidt‐Appleman contrail formation threshold temperature. Here, only a small fraction (<15%) of the emitted soot particles were activated into ice. Our observations enhance the understanding of contrail formation near the formation threshold and give a glimpse on the altitude dependence of climate‐relevant contrail properties.
Highlights
Air traffic has contributed 3.5% to the anthropogenic climate forcing in 2011
Contrail measurements were performed at various altitudes during the 2018 Emission and Climate Impact of Alternative Fuels (ECLIF) II/ NASA DLR Multidisciplinary Airborne Experiment (NDMAX) campaign with the NASA DC-8 chasing the DLR A320
Water vapor was measured by the NASA Langley Diode Laser Hygrometer (DLH), an open-path infrared absorption instrument with a long history of measurements on the DC-8 and many other airborne platforms (Diskin et al, 2002; Podolske et al, 2003)
Summary
Air traffic has contributed 3.5% to the anthropogenic climate forcing in 2011. Contrails and contrail cirrus clouds are accounted for the largest share (Brasseur et al, 2016; Burkhardt & Kärcher, 2011; Kärcher, 2016, 2018; Lee et al, 2020). Flight experiments to investigate contrails have been developed and improved in the last 30 years (Schumann et al, 2017) These observations are important to reduce the uncertainties in the assessment of contrail radiative forcing (Yang et al, 2010). The global radiative influence of contrails on a large scale is discussed by Burkhardt et al (2018), using the global climate model ECHAM5 to show that only a few contrail cirrus outbreaks explain a large percentage of the contrail cirrus climate impact Such outbreak situations can be effectively avoided by routing diversions of air traffic (Teoh et al, 2020). We focus on the dependence of microphysical and optical contrail properties on atmospheric conditions This is possible because a wide range of ambient temperature and water content was measured at altitudes between 7.8 and 11.6 km
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