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Importance of representing optical depth variability for estimates of global line-shaped contrail radiative forcing

Kärcher, Bernd and Burkhardt, Ulrike and Ponater, Michael and Frömming, Christine (2010) Importance of representing optical depth variability for estimates of global line-shaped contrail radiative forcing. Proceedings of the National Academy of Science (PNAS), 45, pp. 19181-19184. DOI: 10.1073/pnas.1005555107.

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Official URL: http://www.pnas.org/content/107/45/19181.full.pdf+html

Abstract

Estimates of the global radiative forcing by line-shaped contrails differ mainly due to the large uncertainty in contrail optical depth. Most contrails are optically thin so that their radiative forcing is roughly proportional to their optical depth and increases with contrail coverage. In recent assessments, the best estimate of mean contrail radiative forcing was significantly reduced, because global climate model simulations pointed at lower optical depth values than earlier studies. We revise these estimates by comparing the probability distribution of contrail optical depth diagnosed with a climate model with the distribution derived from a microphysical, cloud-scale model constrained by satellite observations over the United States. By assuming that the optical depth distribution from the cloud model is more realistic than that from the climate model, and by taking the difference between the observed and simulated optical depth over the United States as globally representative, we quantify uncertainties in the climate model’s diagnostic contrail parameterization. Revising the climate model results accordingly increases the global mean radiative forcing estimate for line-shaped contrails by a factor of 3.3, from 3.5 mW∕m2 to 11.6 mW∕m2 for the year 1992. Furthermore, the satellite observations and the cloud model point at higher global mean optical depth of detectable contrails than often assumed in radiative transfer (off-line) studies. Therefore, we correct estimates of contrail radiative forcing from off-line studies as well. We suggest that the global net radiative forcing of line-shaped persistent contrails is in the range 8–20 mW∕m2 for the air traffic in the year 2000.

Document Type:Article
Title:Importance of representing optical depth variability for estimates of global line-shaped contrail radiative forcing
Authors:
AuthorsInstitution or Email of Authors
Kärcher, BerndUNSPECIFIED
Burkhardt, UlrikeUNSPECIFIED
Ponater, MichaelUNSPECIFIED
Frömming, ChristineUNSPECIFIED
Date:9 November 2010
Journal or Publication Title:Proceedings of the National Academy of Science (PNAS)
Refereed publication:Yes
In Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:45
DOI:10.1073/pnas.1005555107
Page Range:pp. 19181-19184
Status:Published
Keywords:aviation, contrails, radiative forcing
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:L VU - Air Traffic and Environment (old)
DLR - Research area:Aeronautics
DLR - Program:L VU - Air Traffic and Environment
DLR - Research theme (Project):L - Low-Emission Air Traffic (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Atmospheric Trace Species
Deposited By: Prof. Bernd Kärcher
Deposited On:06 Dec 2010 14:58
Last Modified:12 Dec 2013 21:06

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