Ice supersaturation and the potential for contrail formation in a changing climate

Irvine, Emma A.; Shine, Keith P.

doi:10.5194/esd-6-555-2015

Cited by 23 publications

(34 citation statements)

References 56 publications

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“…We find that the RAP dataset is locally ice-supersaturated approximately 12% of the time over an annual cycle at altitudes between 7 km and 13 km. This is lower than some other estimates in the literature with values closer to 15% (Gierens et al 2012, Irvine andShine 2015). However, the RAP dataset is specifically for North America while other results are global.…”

Section: Model Structure and Input Datacontrasting

confidence: 60%

Impact of biofuels on contrail warming

Caiazzo

Agarwal

Speth

et al. 2017

Environ. Res. Lett.

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Contrails and contrail-cirrus may be the largest source of radiative forcing (RF) attributable to aviation. Biomass-derived alternative jet fuels are a potentially major way to mitigate the climate impacts of aviation by reducing lifecycle CO 2 emissions. Given the up to 90% reduction in soot emissions from paraffinic biofuels, the potential for a significant impact on contrail RF due to the reduction in contrail-forming ice nuclei (IN) remains an open question. We simulate contrail formation and evolution to quantify RF over the United States under different emissions scenarios. Replacing conventional jet fuels with paraffinic biofuels generates two competing effects. First, the higher water emissions index results in an increase in contrail occurrence (∼ +8%). On the other hand, these contrails are composed of larger diameter crystals (∼ +58%) at lower number concentrations (∼ −75%), reducing both contrail optical depth (∼ −29%) and albedo (∼ −32%). The net changes in contrail RF induced by switching to biofuels range from −4% to +18% among a range of assumed ice crystal habits (shapes). In comparison, cleaner burning engines (with no increase in water emissions index) result in changes to net contrail RF ranging between −13% and +5% depending on habit. Thus, we find that even 67% to 75% reductions in aircraft soot emissions are insufficient to substantially reduce warming from contrails, and that the use of biofuels may either increase or decrease contrail warming-contrary to previous expectations of a significant decrease in warming.

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Section: Model Structure and Input Datacontrasting

confidence: 60%

Impact of biofuels on contrail warming

Caiazzo

Agarwal

Speth

et al. 2017

Environ. Res. Lett.

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“…The AEDT flight inventory that we use in our model has originally a 1 • × 1 • horizontal resolution with 30 vertical levels, transformed with a recursive discretization method (Jöckel, 2006) to our model resolution. We use inventory data of air traffic density (distance per grid box) and water vapour emissions to initialize contrails in the model.…”

Section: Inventorymentioning

confidence: 99%

“…An increase in atmospheric water vapour concentration may lead to higher contrail cirrus ice water content and optical depths. A decrease in the ice supersaturation frequency (Irvine and Shine, 2015) may result in lower contrail cirrus coverage and associated radiative forcing.…”

Section: Introductionmentioning

confidence: 99%

Contrail cirrus radiative forcing for future air traffic

Bock

Burkhardt

2019

Atmos. Chem. Phys.

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The climate impact of air traffic is to a large degree caused by changes in cirrus cloudiness resulting from the formation of contrails. Contrail cirrus radiative forcing is expected to increase significantly over time due to the large projected increases in air traffic. We use ECHAM5-CCMod, an atmospheric climate model with an online contrail cirrus parameterization including a microphysical two-moment scheme, to investigate the climate impact of contrail cirrus for the year 2050. We take into account the predicted increase in air traffic volume, changes in propulsion efficiency and emissions, in particular soot emissions, and the modification of the contrail cirrus climate impact due to anthropogenic climate change.Global contrail cirrus radiative forcing increases by a factor of 3 from 2006 to 2050, reaching 160 or even 180 mW m −2 , which is the result of the increase in air traffic volume and a slight shift in air traffic towards higher altitudes. Large increases in contrail cirrus radiative forcing are expected over all of the main air traffic areas, but relative increases are largest over main air traffic areas over eastern Asia. The projected upward shift in air traffic attenuates contrail cirrus radiative forcing increases in the midlatitudes but reinforces it in the tropical areas. Climate change has an insignificant impact on global contrail cirrus radiative forcing, while regional changes are significant. Of the emission reductions it is the soot number emission reductions by 50 % that lead to a significant decrease in contrail cirrus optical depth and coverage, leading to a decrease in radiative forcing by approximately 15 %. The strong increase in contrail cirrus radiative forcing due to the projected increase in air traffic volume cannot be compensated for by the decrease in initial ice crystal numbers due to reduced soot emissions and improvements in propulsion efficiency.Published by Copernicus Publications on behalf of the European Geosciences Union.

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“…Quasi-spherical ice prevails also in contrails at low temperatures below about −55 • C. In the core of the contrail, high crystal concentrations reduce the vapour density to saturation, causing the ice particle to retain a nearly spherical shape (Lawson et al, 1998;Lynch, 2001). Contrail cirrus cover is small compared to natural cirrus; nonetheless, they still have a climatic impact with the constant increase in jet aircraft traffic (Stordal et al, 2005;Irvine and Shine, 2015).…”

Section: Introductionmentioning

confidence: 99%

Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment

et al. 2017

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Abstract. Optical probes are frequently used for the detection of microphysical cloud particle properties such as liquid and ice phase, size and morphology. These properties can eventually influence the angular light scattering properties of cirrus clouds as well as the growth and accretion mechanisms of single cloud particles. In this study we compare four commonly used optical probes to examine their response to small cloud particles of different phase and asphericity. Cloud simulation experiments were conducted at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at European Organisation for Nuclear Research (CERN). The chamber was operated in a series of multi-step adiabatic expansions to produce growth and sublimation of ice particles at super-and subsaturated ice conditions and for initial temperatures of −30, −40 and −50 • C. The experiments were performed for ice cloud formation via homogeneous ice nucleation. We report the optical observations of small ice particles in deep convection and in situ cirrus simulations. Ice crystal asphericity deduced from measurements of spatially resolved single particle light scattering patterns by the Particle Phase Discriminator mark 2 (PPD-2K, Karlsruhe edition) were compared with Cloud and Aerosol Spectrometer with Polarisation (CASPOL) measurements and image roundness captured by the 3View Cloud Particle Imager (3V-CPI). Averaged path light scattering properties of the simulated ice clouds were measured using the Scattering Intensity Measurements for the Optical detectioN of icE (SIMONE) and single particle scattering properties were measured by the CASPOL.We show the ambiguity of several optical measurements in ice fraction determination of homogeneously frozen ice in the case where sublimating quasi-spherical ice particles are present. Moreover, most of the instruments have difficulties of producing reliable ice fraction if small aspherical ice particles are present, and all of the instruments cannot separate perfectly spherical ice particles from supercooled droplets. Correlation analysis of bulk averaged path depolarisation measurements and single particle measurements of these clouds showed higher R 2 values at high concentrations and small diameters, but these results require further confirmation. We find that none of these instruments were able to determine unambiguously the phase of the small particles. These results have implications for the interpretation of atmospheric measurements and parametrisations for modelling, particularly for low particle number concentration clouds.

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Ice supersaturation and the potential for contrail formation in a changing climate

Cited by 23 publications

References 56 publications

Impact of biofuels on contrail warming

Impact of biofuels on contrail warming

Contrail cirrus radiative forcing for future air traffic

Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment

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