On the Life Cycle of Individual Contrails and Contrail Cirrus

Abstract The life cycle of individual (initially line shaped) contrails behind aircraft and of contrail cirrus (aged contrails mixed with other ice clouds) is described. The full contrail life cycle is covered, from ice formation for given water, heat, and particulate emissions; to changes in the jet, wake, and dispersion phases; through final sublimation or sedimentation. Contrail properties are deduced from various in situ, remote sensing, and model studies. Aerodynamically induced contrails and distrails are explained briefly. Contrails form both in clear air and inside cirrus. Young contrails consume most of the ambient ice supersaturation. Optical properties of contrails are age and humidity dependent. Contrail occurrence and radiative forcing depends on the ambient Earth–atmosphere conditions. Contrail cirrus seems to be optically thicker than assessed previously and may not only increase cirrus coverage but also thicken existing cirrus. Some observational constraints for contrail cirrus occurrence and radiative forcing are derived. Key parameters controlling contrail properties—besides aircraft and fuel properties, ambient pressure, temperature, and humidity—are the number of ice particles per flight distance surviving the wake vortex phase, the contrail depth, and particle sedimentation, wind shear, turbulence, and vertical motions controlling contrail dispersion. The climate impact of contrails depends among other things on the ratio of shortwave to longwave radiative forcing (RF) and on the efficacy with which contrail RF contributes to surface warming. Several open issues are identified, including renucleation from residuals of sublimated contrail ice particles.

Download Full-text

The evolution of microphysical and optical properties of an A380 contrail in the vortex phase

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-6629-2012 ◽

2012 ◽

Vol 12 (14) ◽

pp. 6629-6643 ◽

Cited By ~ 25

Author(s):

J.-F. Gayet ◽

V. Shcherbakov ◽

C. Voigt ◽

U. Schumann ◽

D. Schäuble ◽

...

Keyword(s):

Crystal Growth ◽

Asymmetry Parameter ◽

Radiative Forcing ◽

Large Body ◽

Climate Impact ◽

Effective Diameter ◽

Ice Crystal ◽

Ice Particles ◽

Research Aircraft ◽

The Asymmetry

Abstract. A contrail from a large-body A380 aircraft at cruise in the humid upper troposphere has been probed with in-situ instruments onboard the DLR research aircraft Falcon. The contrail was sampled during 700 s measurement time at contrail ages of about 1–4 min. The contrail was in the vortex regime during which the primary wake vortices were sinking 270 m below the A380 flight level while the secondary wake remained above. Contrail properties were sampled separately in the primary wake at 90 and 115 s contrail age and nearly continously in the secondary wake at contrail ages from 70 s to 220 s. The scattering phase functions of the contrail particles were measured with a polar nephelometer. The asymmetry parameter derived from these data is used to distinguish between quasi-spherical and aspherical ice particles. In the primary wake, quasi-spherical ice particles were found with concentrations up to 160 cm−3, mean effective diameter Deff of 3.7 μm, maximum extinction of 7.0 km−1, and ice water content (IWC) of 3 mg m−3 at slightly ice-subsaturated conditions. The secondary and primary wakes were separated by an almost particle-free wake vortex gap. The secondary wake contained clearly aspherical contrail ice particles with mean Deff of 4.8 μm, mean (maximum) concentration, extinction, and IWC of 80 (350) cm−3, 1.6 (5.0) km−1, and 2.5 (10) mg m−3, respectively, at conditions apparently above ice-saturation. The asymmetry parameter in the secondary wake decreased with contrail age from 0.87 to 0.80 on average indicating a preferential aspherical ice crystal growth. A retrieval of ice particle habit and size with an inversion code shows that the number fraction of aspherical ice crystals increased from 2% initially to 56% at 4 min contrail age. The observed crystal size and habit differences in the primary and secondary wakes of an up to 4 min old contrail are of interest for understanding ice crystal growth in contrails and their climate impact. Aspherical contrail ice particles cause less radiative forcing than spherical ones.

Download Full-text

Coupled Chemistry-Climate Effects from 2050 Projected Aviation Emissions

10.5194/acp-2017-218 ◽

2017 ◽

Author(s):

Andrew Gettelman ◽

Chih-Chieh Chen ◽

Mark Z. Jacobson ◽

Mary A. Cameron ◽

Donald J. Wuebbles ◽

...

Keyword(s):

Surface Temperature ◽

Black Carbon ◽

Radiative Forcing ◽

Climate Models ◽

Stratospheric Ozone ◽

Climate Impact ◽

Particulate Emissions ◽

Temperature Changes ◽

Climate Effects ◽

Aviation Emissions

Abstract. Analyses of the climate effects of 2050 aviation emissions have been conducted with two coupled Chemistry Climate Models (CCMs) including experiments with coupled ocean models. The baseline 2050 aviation emissions scenario projects emissions ~ 5 times those in 2006. Simulations suggest a corresponding growth in the climate impact of aviation by 2050. Positive radiative forcing from contrails reaches +80 mWm−2. Enhanced upper tropospheric and lower stratospheric ozone (O3) due to aviation nitrogen oxide (NOx) emissions causes a radiative forcing of +60 mWm−2. Changes in methane (CH4) lifetime induced by aviation are estimated to cause −25 mWm−2 of radiative forcing in 2050. Simulations indicate that moderate changes in water vapor emissions from changes in combustion efficiency will not have significant forcing. Non-linear effects due to particles (black carbon and sulfur) included in these calculations suggest an important role for black carbon (BC) in increasing contrail cirrus ice crystal number, leading to net warming. Sulfur emissions brighten clouds and provide a net cooling, but this is dependent on uncertain background sulfur levels. Thus alternative aviation fuels with reduced sulfur and BC may alter the future climate impact of aviation, but the sign is dependent on specific processes represented and the background state. Regional perturbations due to contrail and particulate emissions may result in statistically significant regional surface temperature changes in coupled model simulations in areas near or adjacent to flight corridors, but significant signals only emerge after 20–50 years of simulation. Many regions with high regional aviation forcing do not experience net surface temperature changes because of advective rather than radiative driving of temperatures. Surface temperature signals are not significant globally even in long coupled simulations. Short-lived non-uniform aviation forcing will thus affect climate differently than uniform forcing in the coupled climate system.

Download Full-text

Large ensemble assessment of how the global surface warming response to cumulative carbon differs for negative and positive carbon emissions

10.5194/egusphere-egu21-12718 ◽

2021 ◽

Author(s):

Negar Vakilifard ◽

Katherine Turner ◽

Ric Williams ◽

Philip Holden ◽

Neil Edwards ◽

...

Keyword(s):

Carbon Emissions ◽

Radiative Forcing ◽

Climate Model ◽

Climate Feedback ◽

Climate Response ◽

Ocean Heat Uptake ◽

Transient Climate Response ◽

Surface Warming ◽

Radiative Processes ◽

Negative Emission

The controls of the effective transient climate response (TCRE), defined in terms of the dependence of surface warming since the pre-industrial to the cumulative carbon emission, is explained in terms of climate model experiments for a scenario including positive emissions and then negative emission over a period of 400 years. We employ a pre-calibrated ensemble of GENIE, grid-enabled integrated Earth system model, consisting of 86 members to determine the process of controlling TCRE in both CO2 emissions and drawdown phases. Our results are based on the GENIE simulations with historical forcing from AD 850 including land use change, and the future forcing defined by CO2 emissions and a non-CO2 radiative forcing timeseries. We present the results for the point-source carbon capture and storage (CCS) scenario as a negative emission scenario, following the medium representative concentration pathway (RCP4.5), assuming that the rate of emission drawdown is 2 PgC/yr CO2 for the duration of 100 years. The climate response differs between the periods of positive and negative carbon emissions with a greater ensemble spread during the negative carbon emissions. The controls of the spread in ensemble responses are explained in terms of a combination of thermal processes (involving ocean heat uptake and physical climate feedback), radiative processes (saturation in radiative forcing from CO2 and non-CO2 contributions) and carbon dependences (involving terrestrial and ocean carbon uptake).&#160;&#160;

Download Full-text

Drivers of (non-)linear Eocene surface warming in the DeepMIP ensemble

10.5194/egusphere-egu21-14127 ◽

2021 ◽

Author(s):

Sebastian Steinig ◽

Jiang Zhu ◽

Ran Feng ◽

Keyword(s):

Temperature Gradient ◽

Heat Transport ◽

Climate Sensitivity ◽

Radiative Forcing ◽

Large Scale ◽

Surface Albedo ◽

Early Eocene ◽

Meridional Heat Transport ◽

Surface Warming ◽

Global Mean

The early Eocene greenhouse represents the warmest interval of the Cenozoic and therefore provides a unique opportunity to understand how the climate system operates under elevated atmospheric CO2 levels similar to those projected for the end of the 21st century. Early Eocene geological records indicate a large increase in global mean surface temperatures compared to present day (by ~14&#176;C) and a greatly reduced meridional temperature gradient (by ~30% in SST). However, reproducing these large-scale climate features at reasonable CO2 levels still poses a challenge for current climate models. Recent modelling studies indicate an important role for shortwave (SW) cloud feedbacks to drive increases in climate sensitivity with global warming, which helps to close the gap between simulated and reconstructed Eocene global warmth and temperature gradient. Nevertheless, the presence of such state-dependent feedbacks and their relative strengths in other models remain unclear.In this study, we perform a systematic investigation of the simulated surface warming and the underlying mechanisms in the recently published DeepMIP ensemble. The DeepMIP early Eocene simulations use identical paleogeographic boundary conditions and include six models with suitable output: CESM1.2_CAM5, GFDL_CM2.1, HadCM3B_M2.1aN, IPSLCM5A2, MIROC4m and NorESM1_F. We advance previous energy balance analysis by applying the approximate partial radiative perturbation (APRP) technique to quantify the individual contributions of surface albedo, cloud and non-cloud atmospheric changes to the simulated Eocene top-of-the-atmosphere SW flux anomalies. We further compare the strength of these planetary albedo feedbacks to changes in the longwave atmospheric emissivity and meridional heat transport in the warm Eocene climate. Particular focus lies in the sensitivity of the feedback strengths to increasing global mean temperatures in experiments at a range of atmospheric CO2 concentrations between x1 to x9 preindustrial levels.Preliminary results indicate that all models that provide data for at least 3 different CO2 levels show an increase of the equilibrium climate sensitivity at higher global mean temperatures. This is associated with an increase of the overall strength of the positive SW cloud feedback with warming in those models. This nonlinear behavior seems to be related to both a reduction and optical thinning of low-level clouds, albeit with intermodel differences in the relative importance of the two mechanisms. We further show that our new APRP results can differ significantly from previous estimates based on cloud radiative forcing alone, especially in high-latitude areas with large surface albedo changes. We also find large intermodel variability and state-dependence in meridional heat transport modulated by changes in the atmospheric latent heat transport. Ongoing work focuses on the spatial patterns of the climate feedbacks and the implications for the simulated meridional temperature gradients.

Download Full-text

Sensitivity of Global Warming to Carbon Emissions: Effects of Heat and Carbon Uptake in a Suite of Earth System Models

Journal of Climate ◽

10.1175/jcli-d-16-0468.1 ◽

2017 ◽

Vol 30 (23) ◽

pp. 9343-9363 ◽

Cited By ~ 17

Author(s):

Richard G. Williams ◽

Vassil Roussenov ◽

Philip Goodwin ◽

Laure Resplandy ◽

Laurent Bopp

Keyword(s):

Climate Sensitivity ◽

Carbon Emissions ◽

Radiative Forcing ◽

Carbon Uptake ◽

Earth System ◽

Ocean Heat Uptake ◽

Surface Warming ◽

System Models ◽

Heat Uptake ◽

Earth System Models

Climate projections reveal global-mean surface warming increasing nearly linearly with cumulative carbon emissions. The sensitivity of surface warming to carbon emissions is interpreted in terms of a product of three terms: the dependence of surface warming on radiative forcing, the fractional radiative forcing from CO2, and the dependence of radiative forcing from CO2 on carbon emissions. Mechanistically each term varies, respectively, with climate sensitivity and ocean heat uptake, radiative forcing contributions, and ocean and terrestrial carbon uptake. The sensitivity of surface warming to fossil-fuel carbon emissions is examined using an ensemble of Earth system models, forced either by an annual increase in atmospheric CO2 or by RCPs until year 2100. The sensitivity of surface warming to carbon emissions is controlled by a temporal decrease in the dependence of radiative forcing from CO2 on carbon emissions, which is partly offset by a temporal increase in the dependence of surface warming on radiative forcing. The decrease in the dependence of radiative forcing from CO2 is due to a decline in the ratio of the global ocean carbon undersaturation to carbon emissions, while the increase in the dependence of surface warming is due to a decline in the ratio of ocean heat uptake to radiative forcing. At the present time, there are large intermodel differences in the sensitivity in surface warming to carbon emissions, which are mainly due to uncertainties in the climate sensitivity and ocean heat uptake. These uncertainties undermine the ability to predict how much carbon may be emitted before reaching a warming target.

Download Full-text

A water vapor modulated aerosol impact on ice crystal size

10.5194/acp-2017-548 ◽

2017 ◽

Cited By ~ 1

Author(s):

Bin Zhao ◽

Kuo-Nan Liou ◽

Yu Gu ◽

Jonathan H. Jiang ◽

Qinbin Li ◽

...

Keyword(s):

Water Vapor ◽

Radiative Forcing ◽

Deep Convection ◽

Significant Negative Correlation ◽

Formation Mechanisms ◽

Strong Positive Correlation ◽

Ice Crystal ◽

Ice Clouds ◽

Dry Conditions ◽

The Impact

Abstract. The interactions between aerosols and ice clouds represent one of the largest uncertainties in global radiative forcing from pre-industrial time to the present. In particular, the impact of aerosols on ice crystal effective radius (Rei), which is a key parameter determining ice clouds' net radiative effect, is highly uncertain due to limited and conflicting observational evidence. Here we investigate the effects of aerosols on Rei under different meteorological conditions using 9-year satellite observations. We find that the responses of Rei to aerosol loadings are modulated by water vapor amount in conjunction with several other meteorological parameters. While there is a significant negative correlation between Rei and aerosol loading in moist conditions, consistent with the Twomey effect for liquid clouds, a strong positive correlation between the two occurs in dry conditions. Simulations based on a cloud parcel model suggest that water vapor modulates the relative importance of different ice nucleation modes, leading to the opposite aerosol impacts between moist and dry conditions. When ice clouds are decomposed into those generated from deep convection and formed in-situ, the water vapor modulation remains in effect for both ice cloud types, although the sensitivities of Rei to aerosols differ noticeably between them due to distinct formation mechanisms. The water vapor modulation can largely explain the difference in the responses of Rei to aerosol loadings in various seasons. A proper representation of the water vapor modulation is essential for an accurate estimate of aerosol-cloud radiative forcing produced by ice clouds.

Download Full-text

The global impact of the transport sectors on atmospheric aerosol in 2030 – Part 1: Land transport and shipping

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-22985-2014 ◽

2014 ◽

Vol 14 (16) ◽

pp. 22985-23025

Author(s):

M. Righi ◽

J. Hendricks ◽

R. Sausen

Keyword(s):

Atmospheric Aerosol ◽

Radiative Forcing ◽

Global Climate ◽

Climate Impact ◽

Radiation Budget ◽

Intergovernmental Panel ◽

Surface Level ◽

Aerosol Module ◽

Year 2000 ◽

The Impact

Abstract. Using the EMAC global climate-chemistry model coupled to the aerosol module MADE, we simulate the impact of land transport and shipping emissions on global atmospheric aerosol and climate in 2030. Future emissions of short-lived gas and aerosol species follow the four Representative Concentration Pathways (RCPs) designed in support of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We compare the resulting 2030 land-transport- and shipping-induced aerosol concentrations to the ones obtained for the year 2000 in a previous study with the same model configuration. The simulations suggest that black carbon and aerosol nitrate are the most relevant pollutants from land transport in 2000 and 2030, but their impacts are characterized by very strong regional variations during this time period. Europe and North America experience a decrease in the land-transport-induced particle pollution, although in these regions this sector remains the dominant source of surface-level pollution in 2030 under all RCPs. In Southeast Asia, on the other hand, a significant increase is simulated, but in this region the surface-level pollution is still controlled by other sources than land transport. Shipping-induced air pollution is mostly due to aerosol sulfate and nitrate, which show opposite trends towards 2030. Sulfate is strongly reduced as a consequence of sulfur reduction policies in ship-fuels in force since 2010, while nitrate tends to increase due to the excess of ammonia following the reduction in ammonium-sulfate. The aerosol-induced climate impact of both sectors is dominated by aerosol-cloud effects and is projected to decrease between 2000 and 2030, nevertheless still contributing a significant radiative forcing to the Earth's radiation budget.

Download Full-text

Exploring the uncertainties in the aviation soot–cirrus effect

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-17267-2021 ◽

2021 ◽

Vol 21 (23) ◽

pp. 17267-17289

Author(s):

Mattia Righi ◽

Johannes Hendricks ◽

Christof Gerhard Beer

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Internal Variability ◽

Reanalysis Data ◽

Ice Nucleation ◽

Cirrus Clouds ◽

Model Studies ◽

Model Dynamics ◽

Analogous Model ◽

The Impact

Abstract. A global aerosol–climate model, including a two-moment cloud microphysical scheme and a parametrization for aerosol-induced ice formation in cirrus clouds, is applied in order to quantify the impact of aviation soot on natural cirrus clouds. Several sensitivity experiments are performed to assess the uncertainties in this effect related to (i) the assumptions on the ice nucleation abilities of aviation soot, (ii) the representation of vertical updrafts in the model, and (iii) the use of reanalysis data to relax the model dynamics (the so-called nudging technique). Based on the results of the model simulations, a radiative forcing from the aviation soot–cirrus effect in the range of −35 to 13 mW m−2 is quantified, depending on the assumed critical saturation ratio for ice nucleation and active fraction of aviation soot but with a confidence level below 95 % in several cases. Simple idealized experiments with prescribed vertical velocities further show that the uncertainties on this aspect of the model dynamics are critical for the investigated effect and could potentially add a factor of about 2 of further uncertainty to the model estimates of the resulting radiative forcing. The use of the nudging technique to relax model dynamics is proved essential in order to identify a statistically significant signal from the model internal variability, while simulations performed in free-running mode and with prescribed sea-surface temperatures and sea-ice concentrations are shown to be unable to provide robust estimates of the investigated effect. A comparison with analogous model studies on the aviation soot–cirrus effect show a very large model diversity, with a conspicuous lack of consensus across the various estimates, which points to the need for more in-depth analyses on the roots of such discrepancies.

Download Full-text

The Key Role of Ozone-Depleting Substances in Weakening the Walker Circulation in the Second Half of the Twentieth Century

Journal of Climate ◽

10.1175/jcli-d-17-0906.1 ◽

2019 ◽

Vol 32 (5) ◽

pp. 1411-1418 ◽

Cited By ~ 1

Author(s):

Lorenzo M. Polvani ◽

Katinka Bellomo

Keyword(s):

Twentieth Century ◽

Pacific Ocean ◽

Greenhouse Gases ◽

Radiative Forcing ◽

Climate Model ◽

Walker Circulation ◽

Surface Warming ◽

Ozone Depleting Substances ◽

The Antarctic ◽

The Walker Circulation

It is widely appreciated that ozone-depleting substances (ODS), which have led to the formation of the Antarctic ozone hole, are also powerful greenhouse gases. In this study, we explore the consequence of the surface warming caused by ODS in the second half of the twentieth century over the Indo-Pacific Ocean, using the Whole Atmosphere Chemistry Climate Model (version 4). By contrasting two ensembles of chemistry–climate model integrations (with and without ODS forcing) over the period 1955–2005, we show that the additional greenhouse effect of ODS is crucial to producing a statistically significant weakening of the Walker circulation in our model over that period. When ODS concentrations are held fixed at 1955 levels, the forcing of the other well-mixed greenhouse gases alone leads to a strengthening—rather than weakening—of the Walker circulation because their warming effect is not sufficiently strong. Without increasing ODS, a surface warming delay in the eastern tropical Pacific Ocean leads to an increase in the sea surface temperature gradient between the eastern and western Pacific, with an associated strengthening of the Walker circulation. When increasing ODS are added, the considerably larger total radiative forcing produces a much faster warming in the eastern Pacific, causing the sign of the trend to reverse and the Walker circulation to weaken. Our modeling result suggests that ODS may have been key players in the observed weakening of the Walker circulation over the second half of the twentieth century.

Download Full-text

Transport of the 2017 Canadian wildfire plume to the tropics via the Asian monsoon circulation

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-13547-2019 ◽

2019 ◽

Vol 19 (21) ◽

pp. 13547-13567 ◽

Cited By ~ 8

Author(s):

Corinna Kloss ◽

Gwenaël Berthet ◽

Pasquale Sellitto ◽

Felix Ploeger ◽

Silvia Bucci ◽

...

Keyword(s):

Radiative Forcing ◽

Asian Monsoon ◽

Regional Climate ◽

Climate Impact ◽

Monsoon Circulation ◽

Aerosol Layer ◽

Fire Plume ◽

Monsoon Area ◽

The Tropics ◽

The Impact

Abstract. We show that a fire plume injected into the lower stratosphere at high northern latitudes during the Canadian wildfire event in August 2017 partly reached the tropics. The transport to the tropics was mediated by the anticyclonic flow of the Asian monsoon circulation. The fire plume reached the Asian monsoon area in late August/early September, when the Asian monsoon anticyclone (AMA) was still in place. While there is no evidence of mixing into the center of the AMA, we show that a substantial part of the fire plume is entrained into the anticyclonic flow at the AMA edge and is transported from the extratropics to the tropics, and possibly the Southern Hemisphere particularly following the north–south flow on the eastern side of the AMA. In the tropics the fire plume is lifted by ∼5 km in 7 months. Inside the AMA we find evidence of the Asian tropopause aerosol layer (ATAL) in August, doubling background aerosol conditions with a calculated top of the atmosphere shortwave radiative forcing of −0.05 W m−2. The regional climate impact of the fire signal in the wider Asian monsoon area in September exceeds the impact of the ATAL by a factor of 2–4 and compares to that of a plume coming from an advected moderate volcanic eruption. The stratospheric, trans-continental transport of this plume to the tropics and the related regional climate impact point to the importance of long-range dynamical interconnections of pollution sources.

Download Full-text