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Patrick Minnis - One of the best experts on this subject based on the ideXlab platform.
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Properties of individual Contrails: A compilation of observations and some comparisons
2016Co-Authors: Ulrich Schumann, Patrick Minnis, Sarah T. Bedka, David P. Duda, J.-f. Gayet, Andrew J. Heymsfield, Robert Baumann, Darrel Baumgardner, Volker Freudenthaler, Markus QuanteAbstract:Abstract. Mean properties of individual Contrails are characterized for a wide range of jet aircraft as a function of age during their lifecycle from seconds to 11.5 hours (7.4 to 18.7 km altitude, −88 °C 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 since 1972, and 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 "Contrail library" (COLI). The data are compared with results of the Contrail Cirrus Prediction model CoCiP. 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 “emission index” 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 1015 kg−1. 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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Properties of Linear Contrails Detected in 2012 Northern Hemisphere MODIS Imagery
2015Co-Authors: David P. Duda, Sarah T. Bedka, Thad Chee, Konstantin V. Khlopenkov, Doug Spangenberg, Patrick MinnisAbstract:Observation of linear Contrail cirrus coverage and retrieval of their optical properties are valuable data for validating atmospheric climate models that represent Contrail formation explicitly. These data can reduce our uncertainty of the regional effects of Contrail-generated cirrus on global radiative forcing, and thus improve our estimation of the impact of commercial aviation on climate change. We use an automated Contrail detection algorithm (CDA) to determine the coverage of linear persistent Contrails over the Northern Hemisphere during 2012. The Contrail detection algorithm is a modified form of the Mannstein et al. (1999) method, and uses several channels from thermal infrared MODIS data to reduce the occurrence of false positive detections. A set of Contrail masks of varying sensitivity is produced to define the potential range of uncertainty in Contrail coverage estimated by the CDA. Global aircraft emissions waypoint data provided by FAA allow comparison of detected Contrails with commercial aircraft flight tracks. A pixel-level product based on the advected flight tracks defined by the waypoint data and U-V wind component profiles from the NASA GMAO GEOS-4 reanalysis has been developed to assign a confidence of Contrail detection for the Contrail mask. To account for possible Contrail cirrus missed by the CDA, a post-processing method based on the assumption that pixels adjacent to detected linear Contrails will have radiative signatures similar to those of the detected Contrails is applied to the Northern Hemisphere data. Results from several months of MODIS observations during 2012 will be presented, representing a near-global climatology of Contrail coverage. Linear Contrail coverage will be compared with coverage estimates determined previously from 2006 MODIS data.
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Linear Contrail and Contrail cirrus properties determined from satellite data
Geophysical Research Letters, 2013Co-Authors: Patrick Minnis, Sarah T. Bedka, David P. Duda, Kristopher M. Bedka, Thad Chee, J. Kirk Ayers, Rabindra Palikonda, Douglas A. Spangenberg, Konstantin V. Khlopenkov, R. BoekeAbstract:[1] The properties of Contrail cirrus clouds are retrieved through analysis of Terra and Aqua Moderate Resolution Imaging Spectroradiometer data for 21 cases of spreading linear Contrails. For these cases, Contrail cirrus enhanced the linear Contrail coverage by factors of 2.4–7.6 depending on the Contrail mask sensitivity. In dense air traffic areas, linear Contrail detection sensitivity is apparently reduced when older Contrails overlap and thus is likely diminished during the afternoon. The mean optical depths and effective particle sizes of the Contrail cirrus were 2–3 times and 20% greater, respectively, than the corresponding values retrieved for the adjacent linear Contrails. When Contrails form below, in, or above existing cirrus clouds, the column cloud optical depth is increased and particle size is decreased. Thus, even without increased cirrus coverage, Contrails will affect the radiation balance. These results should be valuable for refining model characterizations of Contrail cirrus needed to fully assess the climate impacts of Contrails.
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estimation of 2006 northern hemisphere Contrail coverage using modis data
Geophysical Research Letters, 2013Co-Authors: David P. Duda, Patrick Minnis, Thad Chee, Konstantin V. Khlopenkov, R. BoekeAbstract:[1] A modified automated Contrail detection algorithm (CDA) using five infrared channels available from the Moderate Resolution Imaging Spectrometer onboard the Aqua satellite is used to determine linear Contrail coverage over the Northern Hemisphere during 2006. Commercial aircraft flight data are employed to filter false Contrail detections by the CDA. The Northern Hemisphere annual mean linear Contrail coverage ranges from 0.07% to 0.40% for three different CDA sensitivities. Based on visual analyses, the medium sensitivity CDA provides the best estimate of linear Contrail coverage, which averages 0.13%. If scaled to the Southern Hemisphere, the global mean coverage would be 0.07%. Coverage is greatest during winter and least during the summer with maximum coverage over the North Atlantic. Less coverage is observed over heavy European and American traffic areas, likely as a result of difficulties in detecting linear Contrails that overlap with each other and with older Contrail cirrus. These results are valuable for evaluating the representation of Contrails and Contrail cirrus within global climate models and for retrieving Contrail optical properties and radiative forcing.
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Parameterization of Contrail radiative properties for climate studies
Geophysical Research Letters, 2012Co-Authors: Yu Xie, Patrick Minnis, Ping Yang, Kuo-nan Liou, David P. DudaAbstract:[1] The study of Contrails and their impact on global climate change requires a cloud model that statistically represents Contrail radiative properties. In this study, the microphysical properties of global Contrails are statistically analyzed using collocated Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) observations. The MODIS Contrail pixels are detected using an automated Contrail detection algorithm and a manual technique using the brightness temperature differences between the MODIS 11 and 12 μm channels. The scattering and absorption properties of typical Contrail ice crystals are used to determine an appropriate Contrail model to minimize the uncertainties arising from the assumptions in a particular cloud model. The depolarization ratio is simulated with a variety of ice crystal habit fractions and matched to the collocated MODIS and CALIOP observations. The Contrail habit fractions are determined and used to compute the bulk-scattering properties of Contrails. A parameterization of shortwave and longwave Contrail optical properties is developed for the spectral bands of the Rapid Radiative Transfer Model (RRTM). The Contrail forcing at the top of the atmosphere is investigated using the RRTM and compared with spherical and hexagonal ice cloud models. Contrail forcing is overestimated when spherical ice crystals are used to represent Contrails, but if a hexagonal ice cloud model is used, the forcing is underestimated for small particles and overestimated for large particles in comparison to the Contrail model developed in this study.
Ulrich Schumann - One of the best experts on this subject based on the ideXlab platform.
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air traffic and Contrail changes during covid 19 over europe amodel study
Atmospheric Chemistry and Physics, 2021Co-Authors: Ulrich Schumann, Roger Teoh, Robert Baumann, Ian Poll, Rainer Koelle, Enrico Spinielli, Jarlath Molloy, George S Koudis, Luca Bugliaro, Marc E.j. StettlerAbstract:Abstract. The strong reduction of air traffic during the COVID-19 pandemic provides a test case for the relation between air traffic density, Contrails, and their radiative forcing of climate change. Air traffic and Contrail cirrus changes are quantified for a European domain for March to August 2020 and compared to the same period in 2019. Traffic data show a 72 % reduction in flight distance compared with 2019. This paper investigates the induced Contrail changes in a model study. The Contrail model results depend on various methodological details tested in parameter studies. In the reference case, the reduced traffic caused an even stronger reduction in Contrail length, partly because the weather conditions in 2020 were less favourable for Contrail formation than in 2019. Contrail coverage over Europe with an optical depth larger than 0.1 decreased from 4.6 % in 2019 to 1.4 % in 2020; total cirrus cover amount changed from 28 to 25 %. The reduced Contrail coverage caused 70 % less longwave and 73 % less shortwave radiative forcing with the consequential reduction of 54 % in the net forcing. The methods include recently developed models for performance parameters and soot emissions. The overall propulsion efficiency of the aircraft is about 20 % smaller than estimated in earlier studies, resulting in 3 % fewer Contrails. Considerable sensitivity to soot emissions is found highlighting fuel and engine importance. The Contrail model includes a new approximate method to account for water vapor exchange between Contrails and background air and for radiative forcing changes due to Contrail-Contrail overlap. The water vapor exchange reduces available ice supersaturation in the atmosphere, which is critical for Contrail formation. Contrail-Contrail overlap changes the computed radiative forcing considerably. Comparisons to satellite observations are to be described in a follow-on paper.
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Beyond Contrail avoidance: Efficacy of flight altitude changes to minimise Contrail climate forcing
Aerospace, 2020Co-Authors: Roger Teoh, Ulrich Schumann, Marc E.j. StettlerAbstract:Abstract: Contrail cirrus introduce a short-lived but significant climate forcing that could be mitigated by small changes in aircraft cruising altitudes. This paper extends a recent study to evaluate the efficacy of several vertical flight diversion strategies to mitigate Contrail climate forcing, and estimates impacts to air traffic management (ATM). We use six one-week periods of flight track data in the airspace above Japan (between May 2012 and March 2013), and simulate Contrails using the Contrail cirrus prediction model (CoCiP). Previous studies have predominantly optimised a diversion of every Contrail-forming flight to minimise its formation or radiative forcing. However, our results show that these strategies produce a suboptimal outcome because most Contrails have a short lifetime, and some have a cooling effect. Instead, a strategy that reroutes 15.3% of flights to avoid long-lived warming Contrails, while allowing for cooling Contrails, reduces the Contrail energy forcing (EF_Contrail) by 105% [91.8, 125%] with a total fuel penalty of 0.70% [0.66, 0.73%]. A minimum EF_total strategy (Contrails + CO2), diverting 20.1% of flights, reduces the EF_Contrail by the same magnitude but also reduces the total fuel consumption by 0.40% [0.31, 0.47%]. For the diversion strategies explored, between 9% and 14% of diversions lead to a loss of separation standards between flights, demonstrating a modest scale of ATM impacts. These results show that small changes in flight altitudes are an opportunity for aviation to significantly and rapidly reduce its effect on the climate.
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On the Life Cycle of Individual Contrails and Contrail Cirrus
Meteorological Monographs, 2017Co-Authors: Ulrich Schumann, A. HeymsfieldAbstract:AbstractThe 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 a...
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Properties of individual Contrails: A compilation of observations and some comparisons
2016Co-Authors: Ulrich Schumann, Patrick Minnis, Sarah T. Bedka, David P. Duda, J.-f. Gayet, Andrew J. Heymsfield, Robert Baumann, Darrel Baumgardner, Volker Freudenthaler, Markus QuanteAbstract:Abstract. Mean properties of individual Contrails are characterized for a wide range of jet aircraft as a function of age during their lifecycle from seconds to 11.5 hours (7.4 to 18.7 km altitude, −88 °C 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 since 1972, and 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 "Contrail library" (COLI). The data are compared with results of the Contrail Cirrus Prediction model CoCiP. 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 “emission index” 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 1015 kg−1. 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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The lifecycle and climate-impact of Contrail cirrus
2016Co-Authors: Ulrich SchumannAbstract:The lifecycle of Contrails and the related climate impact in terms of radiative forcing (RF) is investigated for Contrail cirrus. As a new concept, this study distinguishes between 1) synoptically limited Contrail cirrus, where Contrails form in moderately ice-supersaturated air, but ice particles stay small and Contrails end by sublimation because of drying of the ambient air, e.g., when the ambient air subsides; 2) sedimentation-limited Contrail cirrus, where Contrails form at high humidity with strong supersaturation or in rising air masses, so that the ice particles grow until their fall speed gets large, and the ice particles finally fall to lower levels (e.g. in fall streaks).
Ulrike Burkhardt - One of the best experts on this subject based on the ideXlab platform.
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variability in Contrail ice nucleation and its dependence on soot number emissions
Journal of Geophysical Research, 2019Co-Authors: Andreas Bier, Ulrike BurkhardtAbstract:Contrail ice nucleation is mainly controlled by aircraft emissions and the atmospheric state. The nucleation rate can have a strong impact on microphysical processes, optical properties, lifetime, and, therefore, on the climate impact of Contrail cirrus. We study Contrail ice crystal formation offline forspecified atmospheric conditions and its spatial variability in a global climate model. Assuming the standard atmosphere, above around 270 hPa (10 km) Contrail ice nucleation is mainly controlled by aircraft soot number emissions and below additionally by atmospheric temperature. Parameterizing Contrail ice nucleation in a global climate model, we find that in the northern extratropics Contrails form frequently far away from their formation threshold. For current soot number emissions and in case of Contrail formation, 90% of emitted soot particles form on average ice crystals around the cruise level and more than 70% between cruise altitudes and 300 hPa. The number of nucleated ice crystals in the extratropics decreases nearly at the same rate as soot number emissions. In contrast, in the tropics around cruise altitudes approximately 60% of Contrails develop close to their formation threshold so that on average only about 50% of emitted soot particles can form ice crystals. Below, Contrail formation occurs rarely and ice nucleation is reduced more strongly. Of the main air traffic areas, Contrail ice nucleation is significantly limited by the atmospheric state over eastern Asia and over the southeastern United States. This limitation is enhanced during the summer months.
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Effective radiative forcing of Contrail cirrus
2017Co-Authors: Michael Ponater, Marius Bickel, Lisa Bock, Svenja Reineke, Ulrike BurkhardtAbstract:Contrail cirrus is regarded to make a main contribution to aviation climate impact and is thus playing a key role for respective mitigation considerations. The stratosphere adjusted radiative forcing of line-shaped Contrails has been found to have reduced efficacy in inducing a surface temperature response. Hence, stratosphere adjusted radiative forcing may be of limited value as a metric for the climate impact from Contrails or from Contrail cirrus. Here, we present first results from global climate model simulations designed to determine the effective radiative forcing of Contrail cirrus, as effective radiative forcing is now considered as a more reliable metric. The procedure is not as straightforward as it is for impacts from well-mixed greenhouse gases, because Contrail cirrus forms a spatially and temporally varying perturbation and its impact is small compared to the internal variability simulated by the model for atmospheric radiative fluxes. Yet, by means of a sophisticated modeling strategy it is shown that the effective radiative forcing of Contrail cirrus is indeed significantly smaller than its stratosphere adjusted radiative forcing. Hence, the assumption of a reduced climate impact, compared with what existing radiative forcing estimates have been suggesting, is confirmed by our simulations.
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Effects of optical depth variability on Contrail radiative forcing
Quarterly Journal of the Royal Meteorological Society, 2012Co-Authors: Bernd Kärcher, Ulrike BurkhardtAbstract:Line-shaped Contrails arising from aircraft emissions affect radiative forcing. The magnitude of the radiative forcing from Contrails depends strongly on their optical depth and their spatial and temporal variability caused by dynamical and microphysical processes. Here we investigate the significance of this variability, both for modelling Contrail radiative forcing and estimating thresholds for the detection of Contrails in satellite imagery. Ignoring the variability of Contrail optical depth in models by prescribing a mean optical depth may overestimate mean net radiative forcing by 10−20%. Undersampling of optically thin line-shaped Contrails by passive satellite remote sensing is linked to the inability to detect flux changes in the outgoing long-wave radiation below ≈3 W m−2 for conditions over the eastern North Pacific. Consideration of these findings aids efforts to better quantify uncertainties in aviation climate assessments.
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Sensitivity of Contrail coverage and Contrail radiative forcing to selected key parameters
Atmospheric Environment, 2011Co-Authors: Christine Fromming, Michael Ponater, Ulrike Burkhardt, A. Stenke, S. Pechtl, Robert SausenAbstract:Abstract Estimates of global mean radiative forcing of line-shaped Contrails are associated with a high level of uncertainty. Recent estimates for present day air traffic range from 5.4 mWm−2 to 25.6 mWm−2. The aim of this research paper is to systematically study the sensitivity of Contrail radiative forcing to selected key parameters and to highlight the most important factors for this large uncertainty range, while employing an improved version of the ECHAM climate model. The dominating parameters on Contrail radiative forcing are found to be the detection threshold used for calibrating Contrail coverage to observations, and the mean optical depth. Assuming a detection threshold of 0.05 instead of 0.02 yields an increase of the total coverage, resulting in a 146% increase of global mean Contrail radiative forcing. Employing a globally constant optical depth of up to 0.3, increases the net radiative forcing by 140% over the reference case which has a mean optical depth of 0.08. An upgraded parameterisation of potential Contrail coverage yields a significantly larger amount of tropical Contrails, increasing the Contrail radiative forcing by 53%. The calibration to an alternative observation region along with the assumption of a higher visibility threshold yields an increase of the radiative forcing by 46%. Moderate sensitivity of global Contrail radiative forcing (∼15%) is found for an improvement of model climate and for changes in particle shape. The air traffic inventory, air traffic density parameter, and the diurnal variation of air traffic have only a small effect on global and annual mean Contrail radiative forcing, but their influence on regional and seasonal Contrail radiative forcing may nevertheless be important.
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importance of representing optical depth variability for estimates of global line shaped Contrail radiative forcing
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: B. Kärcher, Michael Ponater, Ulrike Burkhardt, Christine FrommingAbstract: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.
David P. Duda - One of the best experts on this subject based on the ideXlab platform.
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Properties of individual Contrails: A compilation of observations and some comparisons
2016Co-Authors: Ulrich Schumann, Patrick Minnis, Sarah T. Bedka, David P. Duda, J.-f. Gayet, Andrew J. Heymsfield, Robert Baumann, Darrel Baumgardner, Volker Freudenthaler, Markus QuanteAbstract:Abstract. Mean properties of individual Contrails are characterized for a wide range of jet aircraft as a function of age during their lifecycle from seconds to 11.5 hours (7.4 to 18.7 km altitude, −88 °C 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 since 1972, and 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 "Contrail library" (COLI). The data are compared with results of the Contrail Cirrus Prediction model CoCiP. 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 “emission index” 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 1015 kg−1. 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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Properties of Linear Contrails Detected in 2012 Northern Hemisphere MODIS Imagery
2015Co-Authors: David P. Duda, Sarah T. Bedka, Thad Chee, Konstantin V. Khlopenkov, Doug Spangenberg, Patrick MinnisAbstract:Observation of linear Contrail cirrus coverage and retrieval of their optical properties are valuable data for validating atmospheric climate models that represent Contrail formation explicitly. These data can reduce our uncertainty of the regional effects of Contrail-generated cirrus on global radiative forcing, and thus improve our estimation of the impact of commercial aviation on climate change. We use an automated Contrail detection algorithm (CDA) to determine the coverage of linear persistent Contrails over the Northern Hemisphere during 2012. The Contrail detection algorithm is a modified form of the Mannstein et al. (1999) method, and uses several channels from thermal infrared MODIS data to reduce the occurrence of false positive detections. A set of Contrail masks of varying sensitivity is produced to define the potential range of uncertainty in Contrail coverage estimated by the CDA. Global aircraft emissions waypoint data provided by FAA allow comparison of detected Contrails with commercial aircraft flight tracks. A pixel-level product based on the advected flight tracks defined by the waypoint data and U-V wind component profiles from the NASA GMAO GEOS-4 reanalysis has been developed to assign a confidence of Contrail detection for the Contrail mask. To account for possible Contrail cirrus missed by the CDA, a post-processing method based on the assumption that pixels adjacent to detected linear Contrails will have radiative signatures similar to those of the detected Contrails is applied to the Northern Hemisphere data. Results from several months of MODIS observations during 2012 will be presented, representing a near-global climatology of Contrail coverage. Linear Contrail coverage will be compared with coverage estimates determined previously from 2006 MODIS data.
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Linear Contrail and Contrail cirrus properties determined from satellite data
Geophysical Research Letters, 2013Co-Authors: Patrick Minnis, Sarah T. Bedka, David P. Duda, Kristopher M. Bedka, Thad Chee, J. Kirk Ayers, Rabindra Palikonda, Douglas A. Spangenberg, Konstantin V. Khlopenkov, R. BoekeAbstract:[1] The properties of Contrail cirrus clouds are retrieved through analysis of Terra and Aqua Moderate Resolution Imaging Spectroradiometer data for 21 cases of spreading linear Contrails. For these cases, Contrail cirrus enhanced the linear Contrail coverage by factors of 2.4–7.6 depending on the Contrail mask sensitivity. In dense air traffic areas, linear Contrail detection sensitivity is apparently reduced when older Contrails overlap and thus is likely diminished during the afternoon. The mean optical depths and effective particle sizes of the Contrail cirrus were 2–3 times and 20% greater, respectively, than the corresponding values retrieved for the adjacent linear Contrails. When Contrails form below, in, or above existing cirrus clouds, the column cloud optical depth is increased and particle size is decreased. Thus, even without increased cirrus coverage, Contrails will affect the radiation balance. These results should be valuable for refining model characterizations of Contrail cirrus needed to fully assess the climate impacts of Contrails.
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estimation of 2006 northern hemisphere Contrail coverage using modis data
Geophysical Research Letters, 2013Co-Authors: David P. Duda, Patrick Minnis, Thad Chee, Konstantin V. Khlopenkov, R. BoekeAbstract:[1] A modified automated Contrail detection algorithm (CDA) using five infrared channels available from the Moderate Resolution Imaging Spectrometer onboard the Aqua satellite is used to determine linear Contrail coverage over the Northern Hemisphere during 2006. Commercial aircraft flight data are employed to filter false Contrail detections by the CDA. The Northern Hemisphere annual mean linear Contrail coverage ranges from 0.07% to 0.40% for three different CDA sensitivities. Based on visual analyses, the medium sensitivity CDA provides the best estimate of linear Contrail coverage, which averages 0.13%. If scaled to the Southern Hemisphere, the global mean coverage would be 0.07%. Coverage is greatest during winter and least during the summer with maximum coverage over the North Atlantic. Less coverage is observed over heavy European and American traffic areas, likely as a result of difficulties in detecting linear Contrails that overlap with each other and with older Contrail cirrus. These results are valuable for evaluating the representation of Contrails and Contrail cirrus within global climate models and for retrieving Contrail optical properties and radiative forcing.
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Parameterization of Contrail radiative properties for climate studies
Geophysical Research Letters, 2012Co-Authors: Yu Xie, Patrick Minnis, Ping Yang, Kuo-nan Liou, David P. DudaAbstract:[1] The study of Contrails and their impact on global climate change requires a cloud model that statistically represents Contrail radiative properties. In this study, the microphysical properties of global Contrails are statistically analyzed using collocated Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) observations. The MODIS Contrail pixels are detected using an automated Contrail detection algorithm and a manual technique using the brightness temperature differences between the MODIS 11 and 12 μm channels. The scattering and absorption properties of typical Contrail ice crystals are used to determine an appropriate Contrail model to minimize the uncertainties arising from the assumptions in a particular cloud model. The depolarization ratio is simulated with a variety of ice crystal habit fractions and matched to the collocated MODIS and CALIOP observations. The Contrail habit fractions are determined and used to compute the bulk-scattering properties of Contrails. A parameterization of shortwave and longwave Contrail optical properties is developed for the spectral bands of the Rapid Radiative Transfer Model (RRTM). The Contrail forcing at the top of the atmosphere is investigated using the RRTM and compared with spherical and hexagonal ice cloud models. Contrail forcing is overestimated when spherical ice crystals are used to represent Contrails, but if a hexagonal ice cloud model is used, the forcing is underestimated for small particles and overestimated for large particles in comparison to the Contrail model developed in this study.
Bernd Kärcher - One of the best experts on this subject based on the ideXlab platform.
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Effects of optical depth variability on Contrail radiative forcing
Quarterly Journal of the Royal Meteorological Society, 2012Co-Authors: Bernd Kärcher, Ulrike BurkhardtAbstract:Line-shaped Contrails arising from aircraft emissions affect radiative forcing. The magnitude of the radiative forcing from Contrails depends strongly on their optical depth and their spatial and temporal variability caused by dynamical and microphysical processes. Here we investigate the significance of this variability, both for modelling Contrail radiative forcing and estimating thresholds for the detection of Contrails in satellite imagery. Ignoring the variability of Contrail optical depth in models by prescribing a mean optical depth may overestimate mean net radiative forcing by 10−20%. Undersampling of optically thin line-shaped Contrails by passive satellite remote sensing is linked to the inability to detect flux changes in the outgoing long-wave radiation below ≈3 W m−2 for conditions over the eastern North Pacific. Consideration of these findings aids efforts to better quantify uncertainties in aviation climate assessments.
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Global Modeling of the Contrail and Contrail Cirrus Climate Impact
Bulletin of the American Meteorological Society, 2010Co-Authors: Ulrike Burkhardt, Bernd Kärcher, Ulrich SchumannAbstract:Despite considerable technological advances, aviation impacts on global climate are significant and may constitute a future constraint on the continued growth of air travel. The most important but least understood component in aviation climate impact assessments are Contrails, which form as line-shaped ice clouds (linear Contrails) and transform into irregularly shaped ice clouds (Contrail cirrus) in favorable meteorological conditions. No reliable best estimate of the contribution of Contrail cirrus to climate change exists, but statistical evidence from cirrus trend analyses suggests a potentially large contribution. This article reviews the scientific knowledge and key problems regarding the modeling of the life cycle of Contrail cirrus (including linear Contrails), their global climate impact, and the validation of model simulations with suitable observational datasets. The prerequisites for global modeling of Contrail cirrus, such as the representation of ice supersaturation and the processes governi...
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process based simulation of Contrail cirrus in a global climate model
Journal of Geophysical Research, 2009Co-Authors: Ulrike Burkhardt, Bernd KärcherAbstract:[1] Aviation induces changes in global cirrus cloudiness by producing Contrails. In the past, line shaped Contrail coverage has been parameterized relying on the scaling of Contrail formation frequency to observed values. Coverage due to irregularly shaped Contrail cirrus, that develop from line shaped Contrails, could not be estimated with this method. We introduce a process-based parameterization of Contrail cirrus in a global climate model that does not rely on scaling and that is not restricted to line shaped Contrails. A new prognostic cloud class, Contrail cirrus, is introduced that is allowed to develop in the parameterized, fractional ice supersaturated area. Initial dimensions of the Contrails and a parameter controlling their spreading in a sheared flow are constrained by observational data. In an idealized experiment Contrail cirrus coverage is found to be dominated by a major Contrail outbreak and scales with supersaturation rather than Contrail formation frequency. The global distribution of young Contrail coverage is smoothed out due to transport but overall values are similar compared to older estimates. Interannual variability of young Contrail coverage can be as large as the mean coverage. The sensitivity of the model simulations to physical model parameters and to parameters concerning the comparison with observational data is studied. The associated uncertainty of global line shaped Contrail coverage can be as high as 60% of the reference estimate (0.05%). The simulated coverage due to young Contrails agrees reasonably well with most satellite observations of regional line shaped Contrail coverage considering the sensitivity to the above parameters and the interannual variability.
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Process‐based simulation of Contrail cirrus in a global climate model
Journal of Geophysical Research, 2009Co-Authors: Ulrike Burkhardt, Bernd KärcherAbstract:[1] Aviation induces changes in global cirrus cloudiness by producing Contrails. In the past, line shaped Contrail coverage has been parameterized relying on the scaling of Contrail formation frequency to observed values. Coverage due to irregularly shaped Contrail cirrus, that develop from line shaped Contrails, could not be estimated with this method. We introduce a process-based parameterization of Contrail cirrus in a global climate model that does not rely on scaling and that is not restricted to line shaped Contrails. A new prognostic cloud class, Contrail cirrus, is introduced that is allowed to develop in the parameterized, fractional ice supersaturated area. Initial dimensions of the Contrails and a parameter controlling their spreading in a sheared flow are constrained by observational data. In an idealized experiment Contrail cirrus coverage is found to be dominated by a major Contrail outbreak and scales with supersaturation rather than Contrail formation frequency. The global distribution of young Contrail coverage is smoothed out due to transport but overall values are similar compared to older estimates. Interannual variability of young Contrail coverage can be as large as the mean coverage. The sensitivity of the model simulations to physical model parameters and to parameters concerning the comparison with observational data is studied. The associated uncertainty of global line shaped Contrail coverage can be as high as 60% of the reference estimate (0.05%). The simulated coverage due to young Contrails agrees reasonably well with most satellite observations of regional line shaped Contrail coverage considering the sensitivity to the above parameters and the interannual variability.
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Aerodynamic Contrails: Microphysics and Optical Properties
Journal of the Atmospheric Sciences, 2009Co-Authors: Bernd Kärcher, Ulrike Burkhardt, Klaus Gierens, Hermann Mannstein, Bernhard Mayer, Rashiv ChatterjeeAbstract:Aerodynamic Contrails form when air flows across the wings of subsonic aircraft in cruise. During a short adiabatic expansion phase, high supersaturations trigger burstlike homogeneous ice formation on ambient liquid aerosol particles within a wing depth. Small particles freeze first because they equilibrate most rapidly. Ambient temperature is the key determinant of nascent aerodynamic Contrail properties. Only above ;232 K do they become visible (but optically thin). These temperatures are at the high end of those prevailing at tropical upper tropospheric flight levels of subsonic aircraft. In colder midlatitude conditions, aerodynamic Contrails stay invisible and the very small ice particles formed quickly evaporate when exposed to small subsaturations, explaining why the formation of these Contrails is rarely observed. After formation, aerodynamic Contrails develop into Contrail cirrus if air is supersaturated with respect to ice. This type of anthropogenic ice cloud adds to Contrail cirrus derived from jet exhaust Contrails and may become particularly important in the future because air traffic is projected to increase significantly in tropical and subtropical regions. Regardless of whether aerodynamically induced ice formation leads to persistent Contrail cirrus, cruising aircraft may act as sources of potent heterogeneous ice nuclei by preactivating the insoluble fraction in atmospheric particle populations. Aerodynamic Contrails and aerodynamically induced preactivation should therefore be studied experimentally and with global models to explore their potential to induce climate change.