Properties of individual contrails: a compilation of observations and some comparisons
Mean properties of individual contrails are characterized for a wide range of jet aircraft as a function of age during their life cycle from seconds to 11.5 h (7.4–18.7 km altitude, −88 to −31 °C ambient temperature), based on a compilation of about 230 previous in situ and remote sensing measuremen...
Main Authors: | , , , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-01-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | http://www.atmos-chem-phys.net/17/403/2017/acp-17-403-2017.pdf |
Summary: | Mean properties of individual contrails are characterized for a wide range of
jet aircraft as a function of age during their life cycle from seconds to
11.5 h (7.4–18.7 km altitude, −88 to −31 °C ambient
temperature), based on a compilation of about 230 previous in situ and remote
sensing measurements. The airborne, satellite, and ground-based observations
encompass exhaust contrails from jet aircraft from 1972 onwards, as well as a
few older data for propeller aircraft. The contrails are characterized by
mean ice particle sizes and concentrations, extinction, ice water content,
optical depth, geometrical depth, and contrail width. Integral contrail
properties include the cross-section area and total number of ice particles,
total ice water content, and total extinction (area integral of extinction)
per contrail length. When known, the contrail-causing aircraft and ambient
conditions are characterized. The individual datasets are briefly described,
including a few new analyses performed for this study, and compiled together
to form a <q>contrail library</q> (COLI). The data are compared with results of
the Contrail Cirrus Prediction (CoCiP) model. The observations confirm that
the number of ice particles in contrails is controlled by the engine exhaust
and the formation process in the jet phase, with some particle losses in the
wake vortex phase, followed later by weak decreases with time. Contrail cross
sections grow more quickly than expected from exhaust dilution. The
cross-section-integrated extinction follows an algebraic approximation. The
ratio of volume to effective mean radius decreases with time. The ice water
content increases with increasing temperature, similar to non-contrail
cirrus, while the equivalent relative humidity over ice saturation of the
contrail ice mass increases at lower temperatures in the data. Several
contrails were observed in warm air above the Schmidt–Appleman threshold
temperature. The <q>emission index</q> of ice particles, i.e., the number of ice
particles formed in the young contrail per burnt fuel mass, is estimated from
the measured concentrations for estimated dilution; maximum values exceed
10<sup>15</sup> kg<sup>−1</sup>. The dependence of the data on the observation methods is discussed. We find no obvious indication for significant contributions from spurious particles resulting from shattering of ice crystals on the microphysical probes. |
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ISSN: | 1680-7316 1680-7324 |