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Linda Forster
,
Claudia Emde
,
Bernhard Mayer
, and
Simon Unterstrasser

1. Introduction The global radiative forcing (RF) of line-shaped contrails and contrail cirrus calculated by general circulation models (GCMs) exhibits a high level of uncertainty. These uncertainties arise mainly from the radiative transfer models used to calculate the contrail RF as well as from the contrail parameterization and its inherent assumptions employed to represent contrail properties for large grid boxes rather than for individual contrails. A recent study by Frömming et al. (2011

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U. Schumann
,
B. Mayer
,
K. Graf
, and
H. Mannstein

1. Introduction Contrails are aircraft-induced cirrus clouds that may contribute to global warming ( Minnis et al. 1999 ; Fahey et al. 1999 ; Burkhardt and Kärcher 2011 ). At high ambient humidity, contrails develop into contrail cirrus with properties similar to thin natural cirrus ( Schumann 2002 ). Such contrails warm the Earth system during night, but may cool during day, in particular for large solar zenith angles (SZA), small particles, and particle habits with strong sideward

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Burcu Kabatas
,
W. Paul Menzel
,
Ata Bilgili
, and
Liam E. Gumley

Abstract

In this study of ship tracks, Moderate Resolution Imaging Spectroradiometer (MODIS) measurements from late-morning (Terra) and early-afternoon (Aqua) Earth Observing System platforms are analyzed in five separate geographically distributed cases to compare estimates of the sizes (and their changes in time) of droplets associated with ship exhaust. Ship tracks are readily detected in near-infrared imagery as bright features, especially in 2.13-μm observations. The Terra “MOD06” and Aqua “MYD06” cloud products are used to determine the effective radius of the ship-track droplets; droplet age (time in the atmosphere) is estimated as a function of the distance from the ship. Terra and Aqua MODIS estimates of droplet sizes in ship-track plumes are found to be in agreement, with a correlation greater than 0.90; for the cases studied, droplet sizes in the ship plumes are between 6 and 18 μm. Moreover, the droplets’ size growth rates inferred from the length of the ship track were found to average between 0.5 and 1.0 μm h−1.

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D. C. Lewellen

1. Introduction Aircraft contrails represent a unique form of cloud initiation. Starting out highly localized both spatially and temporally, they may sometimes spread over hours to form “natural looking” contrail cirrus where natural cirrus might not arise—for example, in quiescent conditions with negligible vertical velocities. Given projections for increased air traffic in the coming decades it is a concern whether contrails 1 might significantly affect climate. Models designed for assessing

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U. Schumann
,
B. Mayer
,
K. Gierens
,
S. Unterstrasser
,
P. Jessberger
,
A. Petzold
,
C. Voigt
, and
J-F. Gayet

1. Introduction This study addresses the relationship between the optical effective radius r eff and the volume mean radius r vol of ice particles in upper tropospheric ice clouds (cirrus) and aircraft condensation trails (contrails). The effective particle radius is defined such that the extinction coefficient (optical depth) is proportional to the ice water content (IWC) [ice water path (IWP)] divided by the effective radius ( Hansen and Travis 1974 ; Garrett et al. 2003 ). While the

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D. C. Lewellen
,
O. Meza
, and
W. W. Huebsch

1. Introduction It is not uncommon for portions of the upper troposphere to be apparently cloud free (or containing only thin cirrus) yet highly supersaturated with respect to ice (e.g., Gierens et al. 2012 ). For such conditions ice clouds seeded by the passage of aircraft (contrails) can persist and grow into significant cloud cover that at late times could easily be mistaken for natural cirrus ( Minnis et al. 1998 ). Given the projected increases in air traffic in the coming decades and

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Marius Bickel
,
Michael Ponater
,
Lisa Bock
,
Ulrike Burkhardt
, and
Svenja Reineke

understanding for contrail cirrus impact has been thoroughly upgraded during the last 10 years, and it is currently considered as the largest component contributing to aircraft-induced radiative forcing ( Burkhardt and Kärcher 2011 ; Schumann and Graf 2013 ; Bock and Burkhardt 2016b ; Grewe et al. 2017 ). Due to its close link to global mean surface temperature change via the so-called climate sensitivity parameter, radiative forcing has been the established metric base for assessing the relevance of

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Joachim Jansen
and
Andrew J. Heymsfield

1. Introduction Combustion condensation trails, commonly associated with “contrails,” are due to combustion of aircraft fuel and have been widely studied (e.g., the series of articles in the April 2010 issue of the Bulletin of the American Meteorological Society ). These contrails generally occur at temperatures colder than −38°C ( Jensen et al. 1998 ) resulting from the offsetting effects of vapor and heat emitted during combustion ( Schmidt 1941 ; Schumann 1996 ). In contrast, aerodynamic

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Andrew M. Carleton
,
Armand D. Silva
,
Jase Bernhardt
,
Justin VanderBerg
, and
David J. Travis

-crystal clouds—condensation trails, or contrails—that evolve into contrail cirrus, could be the most significant atmospheric effect of commercial aviation ( Burkhardt and Kärcher 2011 ; Burkhardt et al. 2010 ). Persisting contrails on time scales of 1–6 h ( Minnis et al. 1998 ) are likely when cold ambient air is supersaturated with respect to ice (e.g., Appleman 1953 ; Schrader 1997 ; Sausen et al. 1998 ; Minnis et al. 2003 ; Schumann 2005 ; Immler et al. 2008 ; Irvine et al. 2014a ). They

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Ulrich Schumann
and
Andrew J. Heymsfield

1. Introduction Contrails (condensation trails) form behind aircraft as line-shaped cirrus clouds, with high concentrations of small ice particles compared to other cirrus (see Fig. 3-1 ). Contrails may form as “exhaust contrails” from water and particles emitted by the aircraft engines ( Schumann 1996 ) or as “aerodynamic contrails” forming because of adiabatic cooling near curved surfaces of the aircraft ( Gierens et al. 2009 ; Kärcher et al. 2009 ). Distrails (dissipation trails) and

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