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Ulrike Burkhardt - One of the best experts on this subject based on the ideXlab platform.

  • mitigating the contrail Cirrus climate impact by reducing aircraft soot number emissions
    npj Climate and Atmospheric Science, 2018
    Co-Authors: Ulrike Burkhardt, Lisa Bock, Andreas Bier
    Abstract:

    Contrail Cirrus are a major component of the climate forcing due to air traffic. For a given contrail Cirrus cover, ice water content and ice crystal shape, their impact on radiation is dependent on the number and size of ice crystals. Here we use a global climate model to study the impact of a reduction in initially formed ice crystal numbers, as may be caused by reduced soot number emissions. We find that for reduced initial ice crystal numbers the ice water content is decreased and ice crystal sizes increased, leading to a reduction in contrail Cirrus optical depth and doubling the fraction of contrail Cirrus that cannot be detected by satellite remote sensing. Contrail Cirrus lifetimes and coverage are strongly reduced leading to significant reductions in contrail Cirrus radiative forcing. The global climate impact of contrail Cirrus is nonlinearly dependent on the reduction in initial ice crystal numbers. A reduction in the initial ice crystal number of 80% leads to a decrease in contrail Cirrus radiative forcing by 50%, whereas a twofold reduction leads to a decrease in radiative forcing by approximately 20%. Only a few contrail Cirrus outbreaks explain a large percentage of the climate impact. The contrail Cirrus climate impact can be effectively mitigated by reducing initial ice crystal concentrations in such outbreak situations. Our results are important for assessments dealing with mitigating the climate impact of aviation and discussions about the use of alternative fuels or lean combustion in aviation. Reducing soot emissions from aircraft by changing the composition of aviation fuels can effectively mitigate the climate impact of contrail Cirrus. Ulrike Burkhardt and colleagues from the German Aerospace Centre use a global climate model to estimate the impacts of reduced aircraft soot emissions on properties and the climate forcing of contrail Cirrus. Under the low emission condition in which the number of initial ice crystals formed from soot particles is reduced by 80%—a level of reduction that could be obtained using a blend of biofuel and conventional jet fuels—the climate impact of contrail Cirrus is estimated to be reduced by 50%. The mitigation effect occurs predominantly in weather conditions that are favourable for contrail Cirrus outbreaks: with the same level of reduction in the initial ice crystal number, capturing 25% of those events can reduce 30% of the climate forcing caused by contrail Cirrus.

  • Mitigating the contrail Cirrus climate impact by reducing aircraft soot number emissions
    Nature Publishing Group, 2018
    Co-Authors: Ulrike Burkhardt, Lisa Bock, Andreas Bier
    Abstract:

    Atmospheric science: alternative aviation fuel helps mitigate the contrail climate impact Reducing soot emissions from aircraft by changing the composition of aviation fuels can effectively mitigate the climate impact of contrail Cirrus. Ulrike Burkhardt and colleagues from the German Aerospace Centre use a global climate model to estimate the impacts of reduced aircraft soot emissions on properties and the climate forcing of contrail Cirrus. Under the low emission condition in which the number of initial ice crystals formed from soot particles is reduced by 80%—a level of reduction that could be obtained using a blend of biofuel and conventional jet fuels—the climate impact of contrail Cirrus is estimated to be reduced by 50%. The mitigation effect occurs predominantly in weather conditions that are favourable for contrail Cirrus outbreaks: with the same level of reduction in the initial ice crystal number, capturing 25% of those events can reduce 30% of the climate forcing caused by contrail Cirrus

  • synoptic control of contrail Cirrus life cycles and their modification due to reduced soot number emissions
    Journal of Geophysical Research, 2017
    Co-Authors: Andreas Bier, Ulrike Burkhardt, Lisa Bock
    Abstract:

    The atmospheric state, aircraft emissions and engine properties determine formation and initial properties of contrails. The synoptic situation controls microphysical and dynamical processes and causes a wide variability of contrail Cirrus life cycles. A reduction of soot particle number emissions, resulting e.g. from the use of alternative fuels, strongly impacts initial ice crystal numbers and microphysical process rates of contrail Cirrus. We use a climate model including a contrail Cirrus scheme, ECHAM5-CCMod, studying process rates, properties and life cycles of contrail Cirrus clusters within different synoptic situations. The impact of reduced soot number emissions is approximated by a reduction in the initial ice crystal number, exemplarily studied for 80%. Contrail Cirrus microphysical and macrophysical properties can depend much more strongly on the synoptic situation than on the initial ice crystal number. They can attain a large cover, optical depth and ice water content in long-lived and large-scale ice-supersaturated areas, making them particularly climate relevant. In those synoptic situations, the accumulated ice crystal loss due to sedimentation is increased by around 15% and the volume of contrail Cirrus, exceeding an optical depth of 0.02, and their short-wave radiative impact are strongly decreased due to reduced soot emissions. These reductions are of little consequence in short-lived and small-scale ice-supersaturated areas, where contrail Cirrus stay optically very thin and attain a low cover. The synoptic situations in which long-lived and climate relevant contrail Cirrus clusters can be found over the eastern USA occur in around 25% of cases.

  • reassessing properties and radiative forcing of contrail Cirrus using a climate model
    Journal of Geophysical Research, 2016
    Co-Authors: Lisa Bock, Ulrike Burkhardt
    Abstract:

    Contrail Cirrus is the largest known component contributing to the radiative forcing associated with aviation. Despite major advances simulating contrail Cirrus, their microphysical and optical properties and the associated radiative forcing remain largely uncertain. We use a contrail Cirrus parameterization in a global climate model which was extended to include a microphysical two-moment scheme. This allows a more realistic epresentation of microphysical processes, such as deposition and sedimentation, and therefore of the microphysical and optical properties of contrail Cirrus. The simulated contrail microphysical and optical properties agree well with in situ and satellite observations. As compared to estimates using an older version of the contrail Cirrus scheme, the optical depth of contrail Cirrus is significantly higher, particularly in regions with high air traffic density, due to high ice crystal number concentrations on the main flight routes. Nevertheless, the estimated radiative forcing for the year 2002 supports our earlier results. The global radiative forcing of contrail Cirrus for the year 2006 is estimated to be 56mW/m2. A large uncertainty of the radiative forcing estimate appears to be connected with the, on average, very small ice crystal radii simulated in the main air traffic areas, which make the application of a radiative transfer parameterization based on geometric optics questionable.

  • the temporal evolution of a long lived contrail Cirrus cluster simulations with a global climate model
    Journal of Geophysical Research, 2016
    Co-Authors: Lisa Bock, Ulrike Burkhardt
    Abstract:

    The representation of contrail Cirrus in climate models has advanced in the last years tremendously. Nevertheless, uncertainties in particular regarding the representation of contrail microphysics still remain. Properties of young contrail Cirrus differ from those of natural Cirrus due to the large ice crystal number concentration common in contrails. Consequently, microphysical process rates in contrail Cirrus, which control its lifetime, can be very different to those in natural Cirrus. We extend a contrail Cirrus scheme within a climate model by implementing a microphysical two-moment scheme and study the life cycle of a contrail Cirrus cluster. In an idealized experiment we study the properties and microphysical process rates of a contrail Cirrus cluster in a large and long-lived ice supersaturated region. We find that at flight level contrail Cirrus display their typical high ice crystal number concentration (of about 10–100 cm−3) for a few hours with far lower densities in lower levels caused by sedimentation. After about 7 h contrail Cirrus have spread considerably so that even at flight level associated ice crystal number concentrations have dropped to values that prohibit fast relaxation of ice supersaturation. The reduced ice crystal number and the resulting limited water uptake in the contrail Cirrus limit the lifetime of the contrail Cirrus cluster to about 10 h even though surrounding conditions would be still favorable for contrail Cirrus persistence. In our case studies, contrail Cirrus resembles natural Cirrus regarding their ice crystal number concentration and size after 5–7 h.

Lisa Bock - One of the best experts on this subject based on the ideXlab platform.

  • mitigating the contrail Cirrus climate impact by reducing aircraft soot number emissions
    npj Climate and Atmospheric Science, 2018
    Co-Authors: Ulrike Burkhardt, Lisa Bock, Andreas Bier
    Abstract:

    Contrail Cirrus are a major component of the climate forcing due to air traffic. For a given contrail Cirrus cover, ice water content and ice crystal shape, their impact on radiation is dependent on the number and size of ice crystals. Here we use a global climate model to study the impact of a reduction in initially formed ice crystal numbers, as may be caused by reduced soot number emissions. We find that for reduced initial ice crystal numbers the ice water content is decreased and ice crystal sizes increased, leading to a reduction in contrail Cirrus optical depth and doubling the fraction of contrail Cirrus that cannot be detected by satellite remote sensing. Contrail Cirrus lifetimes and coverage are strongly reduced leading to significant reductions in contrail Cirrus radiative forcing. The global climate impact of contrail Cirrus is nonlinearly dependent on the reduction in initial ice crystal numbers. A reduction in the initial ice crystal number of 80% leads to a decrease in contrail Cirrus radiative forcing by 50%, whereas a twofold reduction leads to a decrease in radiative forcing by approximately 20%. Only a few contrail Cirrus outbreaks explain a large percentage of the climate impact. The contrail Cirrus climate impact can be effectively mitigated by reducing initial ice crystal concentrations in such outbreak situations. Our results are important for assessments dealing with mitigating the climate impact of aviation and discussions about the use of alternative fuels or lean combustion in aviation. Reducing soot emissions from aircraft by changing the composition of aviation fuels can effectively mitigate the climate impact of contrail Cirrus. Ulrike Burkhardt and colleagues from the German Aerospace Centre use a global climate model to estimate the impacts of reduced aircraft soot emissions on properties and the climate forcing of contrail Cirrus. Under the low emission condition in which the number of initial ice crystals formed from soot particles is reduced by 80%—a level of reduction that could be obtained using a blend of biofuel and conventional jet fuels—the climate impact of contrail Cirrus is estimated to be reduced by 50%. The mitigation effect occurs predominantly in weather conditions that are favourable for contrail Cirrus outbreaks: with the same level of reduction in the initial ice crystal number, capturing 25% of those events can reduce 30% of the climate forcing caused by contrail Cirrus.

  • Mitigating the contrail Cirrus climate impact by reducing aircraft soot number emissions
    Nature Publishing Group, 2018
    Co-Authors: Ulrike Burkhardt, Lisa Bock, Andreas Bier
    Abstract:

    Atmospheric science: alternative aviation fuel helps mitigate the contrail climate impact Reducing soot emissions from aircraft by changing the composition of aviation fuels can effectively mitigate the climate impact of contrail Cirrus. Ulrike Burkhardt and colleagues from the German Aerospace Centre use a global climate model to estimate the impacts of reduced aircraft soot emissions on properties and the climate forcing of contrail Cirrus. Under the low emission condition in which the number of initial ice crystals formed from soot particles is reduced by 80%—a level of reduction that could be obtained using a blend of biofuel and conventional jet fuels—the climate impact of contrail Cirrus is estimated to be reduced by 50%. The mitigation effect occurs predominantly in weather conditions that are favourable for contrail Cirrus outbreaks: with the same level of reduction in the initial ice crystal number, capturing 25% of those events can reduce 30% of the climate forcing caused by contrail Cirrus

  • synoptic control of contrail Cirrus life cycles and their modification due to reduced soot number emissions
    Journal of Geophysical Research, 2017
    Co-Authors: Andreas Bier, Ulrike Burkhardt, Lisa Bock
    Abstract:

    The atmospheric state, aircraft emissions and engine properties determine formation and initial properties of contrails. The synoptic situation controls microphysical and dynamical processes and causes a wide variability of contrail Cirrus life cycles. A reduction of soot particle number emissions, resulting e.g. from the use of alternative fuels, strongly impacts initial ice crystal numbers and microphysical process rates of contrail Cirrus. We use a climate model including a contrail Cirrus scheme, ECHAM5-CCMod, studying process rates, properties and life cycles of contrail Cirrus clusters within different synoptic situations. The impact of reduced soot number emissions is approximated by a reduction in the initial ice crystal number, exemplarily studied for 80%. Contrail Cirrus microphysical and macrophysical properties can depend much more strongly on the synoptic situation than on the initial ice crystal number. They can attain a large cover, optical depth and ice water content in long-lived and large-scale ice-supersaturated areas, making them particularly climate relevant. In those synoptic situations, the accumulated ice crystal loss due to sedimentation is increased by around 15% and the volume of contrail Cirrus, exceeding an optical depth of 0.02, and their short-wave radiative impact are strongly decreased due to reduced soot emissions. These reductions are of little consequence in short-lived and small-scale ice-supersaturated areas, where contrail Cirrus stay optically very thin and attain a low cover. The synoptic situations in which long-lived and climate relevant contrail Cirrus clusters can be found over the eastern USA occur in around 25% of cases.

  • reassessing properties and radiative forcing of contrail Cirrus using a climate model
    Journal of Geophysical Research, 2016
    Co-Authors: Lisa Bock, Ulrike Burkhardt
    Abstract:

    Contrail Cirrus is the largest known component contributing to the radiative forcing associated with aviation. Despite major advances simulating contrail Cirrus, their microphysical and optical properties and the associated radiative forcing remain largely uncertain. We use a contrail Cirrus parameterization in a global climate model which was extended to include a microphysical two-moment scheme. This allows a more realistic epresentation of microphysical processes, such as deposition and sedimentation, and therefore of the microphysical and optical properties of contrail Cirrus. The simulated contrail microphysical and optical properties agree well with in situ and satellite observations. As compared to estimates using an older version of the contrail Cirrus scheme, the optical depth of contrail Cirrus is significantly higher, particularly in regions with high air traffic density, due to high ice crystal number concentrations on the main flight routes. Nevertheless, the estimated radiative forcing for the year 2002 supports our earlier results. The global radiative forcing of contrail Cirrus for the year 2006 is estimated to be 56mW/m2. A large uncertainty of the radiative forcing estimate appears to be connected with the, on average, very small ice crystal radii simulated in the main air traffic areas, which make the application of a radiative transfer parameterization based on geometric optics questionable.

  • the temporal evolution of a long lived contrail Cirrus cluster simulations with a global climate model
    Journal of Geophysical Research, 2016
    Co-Authors: Lisa Bock, Ulrike Burkhardt
    Abstract:

    The representation of contrail Cirrus in climate models has advanced in the last years tremendously. Nevertheless, uncertainties in particular regarding the representation of contrail microphysics still remain. Properties of young contrail Cirrus differ from those of natural Cirrus due to the large ice crystal number concentration common in contrails. Consequently, microphysical process rates in contrail Cirrus, which control its lifetime, can be very different to those in natural Cirrus. We extend a contrail Cirrus scheme within a climate model by implementing a microphysical two-moment scheme and study the life cycle of a contrail Cirrus cluster. In an idealized experiment we study the properties and microphysical process rates of a contrail Cirrus cluster in a large and long-lived ice supersaturated region. We find that at flight level contrail Cirrus display their typical high ice crystal number concentration (of about 10–100 cm−3) for a few hours with far lower densities in lower levels caused by sedimentation. After about 7 h contrail Cirrus have spread considerably so that even at flight level associated ice crystal number concentrations have dropped to values that prohibit fast relaxation of ice supersaturation. The reduced ice crystal number and the resulting limited water uptake in the contrail Cirrus limit the lifetime of the contrail Cirrus cluster to about 10 h even though surrounding conditions would be still favorable for contrail Cirrus persistence. In our case studies, contrail Cirrus resembles natural Cirrus regarding their ice crystal number concentration and size after 5–7 h.

B Karcher - One of the best experts on this subject based on the ideXlab platform.

  • formation and radiative forcing of contrail Cirrus
    Nature Communications, 2018
    Co-Authors: B Karcher
    Abstract:

    Aircraft-produced contrail Cirrus clouds contribute to anthropogenic climate change. Observational data sets and modelling approaches have become available that clarify formation pathways close to the source aircraft and lead to estimates of the global distribution of their microphysical and optical properties. While contrail Cirrus enhance the impact of natural clouds on climate, uncertainties remain regarding their properties and lifecycle. Progress in representing aircraft emissions, contrail Cirrus and natural Cirrus in global climate models together with tighter constraints on the sensitivity of the climate system will help judge efficiencies of and trade-offs between mitigation options.

  • Cirrus parcel model comparison project phase 1 the critical components to simulate Cirrus initiation explicitly
    2013
    Co-Authors: E J Jensen, David Oc Starr, Kenneth Sassen, B Karcher, Rueifong Lin, Paul J Demott, Richard Cotton, Xiaohong Liu
    Abstract:

    Abstract The Cirrus Parcel Model Comparison Project, a project of the GCSS [Global Energy and Water Cycle Experiment (GEWEX) Cloud System Studies] Working Group on Cirrus Cloud Systems, involves the systematic comparison of current models of ice crystal nucleation and growth for specified, typical, Cirrus cloud environments. In Phase 1 of the project reported here, simulated Cirrus cloud microphysical properties from seven models are compared for “warm” (−40°C) and “cold” (−60°C) Cirrus, each subject to updrafts of 0.04, 0.2, and 1 m s−1. The models employ explicit microphysical schemes wherein the size distribution of each class of particles (aerosols and ice crystals) is resolved into bins or the evolution of each individual particle is traced. Simulations are made including both homogeneous and heterogeneous ice nucleation mechanisms (all-mode simulations). A single initial aerosol population of sulfuric acid particles is prescribed for all simulations. Heterogeneous nucleation is disabled for a second...

  • effects of ice nuclei on Cirrus clouds in a global climate model
    Journal of Geophysical Research, 2011
    Co-Authors: Johannes Hendricks, B Karcher, Ulrike Lohmann
    Abstract:

    [1] A multiple-mode ice microphysical scheme is applied in the European Centre/Hamburg (ECHAM) general circulation model to simulate effects of aerosol-ice interactions on global Cirrus properties. The different ice modes represent Cirrus ice formed by homogeneous freezing of liquid aerosols and heterogeneous nucleation on mineral dust or black carbon particles. A fourth ice mode represents ice from other sources. The competition of these modes for available water is realized in a physical parameterization scheme considering also the effect of preexisting ice on the ice nucleation process. The model is applied to analyze the global characteristics of ice formed by the different aerosol types and to study potential global effects of mineral dust and black carbon particles on Cirrus microphysical parameters. The simulations reveal that, on average, ice from heterogeneous nucleation shows fewer but larger crystals and has a smaller contribution to the mean Cirrus ice water content than ice from homogeneous freezing. However, heterogeneous ice nuclei may have important effects on the overall Cirrus properties. Reductions in zonal mean annual average Cirrus ice particle number concentrations induced by heterogeneous nucleation of up to 20% in the tropics and 1%–10% in the midlatitudes are simulated. The effect is further amplified by ice formation on aircraft-generated soot. Significant reductions in the mean ice water content are modeled, which likely result from efficient sedimentation and precipitation of large ice particles generated by heterogeneous nucleation. This leads to reductions in the zonal mean annual average water vapor mixing ratio of up to 5% at Cirrus levels.

  • the impact of aerosols and gravity waves on Cirrus clouds at midlatitudes
    Journal of Geophysical Research, 2004
    Co-Authors: W Haag, B Karcher
    Abstract:

    [1] We use a Lagrangian microphysical aerosol-cloud model to simulate Cirrus clouds along trajectories at northern hemisphere midlatitudes. The model is constrained by recent in situ observations in terms of aerosol size distributions, freezing relative humidities, cooling rates, and Cirrus particle sedimentation rates. Key features include competition between insoluble and volatile aerosol particles and temperature perturbations induced by high-frequency gravity waves. Recent analyses of field measurements have revealed the crucial roles both factors play in Cirrus formation. We show that most Cirrus form in synoptic cold pools, but with microphysical properties determined by mesoscale variability in vertical velocities. Heterogeneous ice nuclei (IN) present in concentrations probably typical for northern midlatitude background conditions (<0.01–0.03 cm−3) significantly modify Cirrus properties but do not control Cirrus formation. The key effect of IN on Cirrus clouds is a reduction of the number of ice crystals. This indirect aerosol effect results in reduced cloud albedo due to increased effective radii and decreased ice water contents, as well as in nonlinear changes of Cirrus occurrence, optical extinction, and fraction of clouds that are subvisible. The nonlinear dependence of the three latter quantities appears when IN concentrations rise above a threshold concentration of some 0.01 cm−3, the exact value depending on the cloud formation temperature, cooling rate, and IN freezing relative humidity. In such conditions, IN become the controlling factor in Cirrus formation, diminishing the role of homogeneous freezing. Ice nuclei with freezing thresholds near ice saturation are capable of introducing strong changes of cloud properties, even at low concentrations. Optically thin and subvisible Cirrus are particularly susceptible to IN. The presence of a small number of IN (0.001 cm−3) can significantly increase their occurrence frequencies. If such clouds predominantly form on IN, they might be affected by anthropogenic activities. Changes in upper tropospheric cooling rates and ice-forming aerosols in a future climate may induce changes in Cirrus occurrence that are comparable in magnitude to observed decadal trends in global Cirrus cover.

  • nitric acid uptake on subtropical Cirrus cloud particles
    Journal of Geophysical Research, 2004
    Co-Authors: P J Popp, B Karcher, R S Gao, D W Fahey, T P Marcy, P K Hudson, T L Thompson, B A Ridley, A J Weinheimer, D J Knapp
    Abstract:

    The redistribution of HNO 3 via uptake and sedimentation by Cirrus cloud particles is considered an important term in the upper tropospheric budget of reactive nitrogen. Numerous Cirrus cloud encounters by the NASA WB-57F high-altitude research aircraft during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) were accompanied by the observation of condensed-phase HNO 3 with the NOAA chemical ionization mass spectrometer. The instrument measures HNO 3 with two independent channels of detection connected to separate forward and downward facing inlets that allow a determination of the amount of HNO 3 condensed on ice particles. Subtropical Cirrus clouds, as indicated by the presence of ice particles, were observed coincident with condensed-phase HNO 3 at temperatures of 197-224 K and pressures of 122-224 hPa. Maximum levels of condensed-phase HNO 3 approached the gas-phase equivalent of 0.8 ppbv. Ice particle surface coverages as high as 1.4 x 10 14 molecules cm -2 were observed. A dissociative Langmuir adsorption model, when using an empirically derived HNO 3 adsorption enthalpy of -11.0 kcal mol -1 , electively describes the observed molecular coverages to within a factor of 5. The percentage of total HNO 3 in the condensed phase ranged from near zero to 100% in the observed Cirrus clouds. With volume-weighted mean particle diameters up to 700 μm and particle fall velocities up to 10 m s -1 , some observed clouds have significant potential to redistribute HNO 3 in the upper troposphere.

William B Rossow - One of the best experts on this subject based on the ideXlab platform.

  • B.: Characterizing tropical Cirrus life cycle, evolution, and interaction with upper-tropospheric water vapor using Lagrangian trajectory analysis of satellite observations
    2016
    Co-Authors: Zhengzhao Luo, William B Rossow
    Abstract:

    Tropical Cirrus evolution and its relation to upper-tropospheric water vapor (UTWV) are examined in the paper by analyzing satellite-derived cloud data, UTWV data from infrared and microwave measurements, and the NCEP–NCAR reanalysis wind field. Building upon the existing International Satellite Cloud Climatology Project (ISCCP) data and the Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) product, a global (except polar region), 6-hourly Cirrus dataset is developed from two infrared radiance measurements at 11 and 12 mm. The UTWV is obtained in both clear and cloudy locations by developing a combined satellite infrared and microwave-based retrieval. The analysis in this study is conducted in a Lagrangian framework. The Lagrangian trajectory analysis shows that the decay of deep convection is immediately followed by the growth of cirrostratus and Cirrus, and then the decay of cirrostratus is followed by the continued growth of Cirrus. Cirrus properties continuously evolve along the trajectories as they gradually thin out and move to the lower levels. Typical tropical Cirrus systems last for 19–30 6 16 h. This is much longer than Cirrus particle lifetimes, suggesting that other processes (e.g., large-scale lifting) replenish the particles to maintain tropical Cirrus. Consequently, tropical Cirrus can advect over large distances, about 600–1000 km, during their lifetimes. For almost all current GCMs, this distance spans more than one grid box, requiring that the water vapor an

  • characterizing tropical Cirrus life cycle evolution and interaction with upper tropospheric water vapor using lagrangian trajectory analysis of satellite observations
    Journal of Climate, 2004
    Co-Authors: William B Rossow
    Abstract:

    Abstract Tropical Cirrus evolution and its relation to upper-tropospheric water vapor (UTWV) are examined in the paper by analyzing satellite-derived cloud data, UTWV data from infrared and microwave measurements, and the NCEP–NCAR reanalysis wind field. Building upon the existing International Satellite Cloud Climatology Project (ISCCP) data and the Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) product, a global (except polar region), 6-hourly Cirrus dataset is developed from two infrared radiance measurements at 11 and 12 μm. The UTWV is obtained in both clear and cloudy locations by developing a combined satellite infrared and microwave-based retrieval. The analysis in this study is conducted in a Lagrangian framework. The Lagrangian trajectory analysis shows that the decay of deep convection is immediately followed by the growth of cirrostratus and Cirrus, and then the decay of cirrostratus is followed by the continued growth of Cirrus. Cirrus properties con...

  • characterizing tropical Cirrus life cycle evolution and interaction with upper tropospheric water vapor using lagrangian trajectory analysis of satellite observations
    Journal of Climate, 2004
    Co-Authors: Zhengzhao Luo, William B Rossow
    Abstract:

    Tropical Cirrus evolution and its relation to upper-tropospheric water vapor (UTWV) are examined in the paper by analyzing satellite-derived cloud data, UTWV data from infrared and microwave measurements, and the NCEP‐NCAR reanalysis wind field. Building upon the existing International Satellite Cloud Climatology Project (ISCCP) data and the Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) product, a global (except polar region), 6-hourly Cirrus dataset is developed from two infrared radiance measurements at 11 and 12 mm. The UTWV is obtained in both clear and cloudy locations by developing a combined satellite infrared and microwave-based retrieval. The analysis in this study is conducted in a Lagrangian framework. The Lagrangian trajectory analysis shows that the decay of deep convection is immediately followed by the growth of cirrostratus and Cirrus, and then the decay of cirrostratus is followed by the continued growth of Cirrus. Cirrus properties continuously evolve along the trajectories as they gradually thin out and move to the lower levels. Typical tropical Cirrus systems last for 19‐30 6 16 h. This is much longer than Cirrus particle lifetimes, suggesting that other processes (e.g., large-scale lifting) replenish the particles to maintain tropical Cirrus. Consequently, tropical Cirrus can advect over large distances, about 600‐1000 km, during their lifetimes. For almost all current GCMs, this distance spans more than one grid box, requiring that the water vapor and cloud water budgets include an advection term. Based on their relationship to convective systems, detrainment Cirrus are distinguished from in situ Cirrus. It is found that more than half of the tropical Cirrus are formed in situ well away from convection. The interaction between Cirrus and UTWV is explored by comparing the evolution of the UTWV along composite clear trajectories and trajectories with Cirrus. Cirrus are found to be associated with a moister upper troposphere and a slower rate of decrease of UTWV. Moreover, the elevated UTWV has a longer duration than Cirrus. The amount of water in Cirrus is too small for evaporation of Cirrus ice particles to moisten the upper troposphere significantly (but Cirrus may be an important water vapor sink). Rather, it is likely that the same transient motions that produce the Cirrus also transport water vapor upward to maintain a larger UTWV.

  • is there a trend in Cirrus cloud cover due to aircraft traffic
    Atmospheric Chemistry and Physics, 2004
    Co-Authors: William B Rossow, Frode Stordal, Gunnar Myhre, E J G Stordal, David S Lee, D W Arlander, Tove Marit Svendby
    Abstract:

    Abstract. Trends in Cirrus cloud cover have been estimated based on 16 years of data from ISCCP (International Satellite Cloud Climatology Project). The results have been spatially correlated with aircraft density data to determine the changes in Cirrus cloud cover due to aircraft traffic. The correlations are only moderate, as many other factors have also contributed to changes in Cirrus. Still we regard the results to be indicative of an impact of aircraft on Cirrus amount. The main emphasis of our study is on the area covered by the METEOSAT satellite to avoid trends in the ISCCP data resulting from changing satellite viewing geometry. In Europe, which is within the METEOSAT region, we find indications of a trend of about 1-2% cloud cover per decade due to aircraft, in reasonable agreement with previous studies. The positive trend in Cirrus in areas of high aircraft traffic contrasts with a general negative trend in Cirrus. Extrapolation in time to cover the entire period of aircraft operations and in space to cover the global scale yields a mean estimate of 0.03 Wm-2 (lower limit 0.01, upper limit 0.08 Wm-2) for the radiative forcing due to aircraft induced Cirrus. The mean is close to the value given by IPCC (1999) as an upper limit.

Armin Afchine - One of the best experts on this subject based on the ideXlab platform.

  • a microphysics guide to Cirrus part ii climatologies of clouds and humidity from observations
    Atmospheric Chemistry and Physics, 2020
    Co-Authors: Martina Kramer, E J Jensen, Armin Afchine, Christian Rolf, Nicole Spelten, D W Fahey, Sergey Khaykin, Thomas Kuhn, P Lawson, Alexey Lykov
    Abstract:

    This study presents airborne in-situ and satellite remote sensing climatologies of Cirrus clouds and humidity. The climatologies serve as a guide to the properties of Cirrus clouds, with the new in-situ data base providing detailed insights into boreal mid-latitudes and the tropics, while the satellite-borne data set offers a global overview. To this end, an extensive, quality checked data archive, the Cirrus Guide II in-situ data base, is created from airborne in-situ measurements during 150 flights in 24 campaigns. The archive contains meteorological parameters, IWC, Nice, Rice, RHice and H2O for each of the flights (IWC: ice water content, Nice: number concentration of ice crystals, Rice: ice crystal mean mass radius, RHice: relative humidity with respect to ice, H2O: water vapor mixing ratio). Depending on the specific parameter, the data base has extended by about a factor of 5–10 compared to the previous studies of Schiller et al. (2008), JGR, and Kramer et al. (2009), ACP. One result of our investigations is, that across all latitudes, the thicker liquid origin Cirrus predominate at lower altitudes, while at higher altitudes the thinner in-situ Cirrus prevail. Further, exemplary investigations of the radiative characteristics of in-situ and liquid origin Cirrus show that the in-situ origin Cirrus only slightly warm the atmosphere, while liquid origin Cirrus have a strong cooling effect. An important step in completing the Cirrus Guide II is the provision of the global Cirrus Nice climatology, derived by means of the retrieval algorithm DARDAR-Nice from ten years of Cirrus remote sensing observations from satellite. The in-situ data base has been used to evaluate and adjust the satellite observations. We found that the global median Nice from satellite observations is almost two times higher than the in-situ median and increases slightly with decreasing temperature. Nice medians of the most frequentl occuring Cirrus sorted by geographical regions are highest in the tropics, followed by austral/boreal mid-latitudes, Antarctica and the Arctic. Since the satellite climatologies enclose the entire spatial and temporal Nice occurrence, we could deduce that half of the Cirrus are located in the lowest, warmest Cirrus layer and contain a significant amount of liquid origin Cirrus. A specific highlight of the study is the in-situ observations of tropical tropopause layer (TTL) Cirrus and humidity in the Asian monsoon anticyclone and the comparison to the surrounding tropics. In the convectively very active Asian monsoon, peak values of Nice and IWC of 30 ppmv and 1000 ppmv are detected around the cold point tropopause (CPT). Above the CPT, ice particles that are convectively injected can locally add a significant amount of water available for exchange with the stratosphere. We found IWCs of up to 8 ppmv in the Asian monsoon in comparison to only 2 ppmv in the surrounding tropics. Also, the highest RHice inside of the clouds as well as in clear sky (120–150 %) are observed around and above the CPT. We attribute this to the high amount of H2O (3–5 ppmv) in comparison to 1.5–3 ppmv in other tropical regions. The supersaturations above the CPT suggest that the water exchange with the stratosphere is 10–20 % higher than expected in regions of weak convective activity and up to about 50 % in the Asian monsoon.

  • A microphysics guide to Cirrus – Part 2: Climatologies of clouds and humidity from observations
    Atmospheric Chemistry and Physics, 2020
    Co-Authors: Martina Kramer, Armin Afchine, Christian Rolf, Nicole Spelten, Paul Lawson, Sergey Khaykin, Thomas Kuhn, David Fahey, Eric Jensen, Alexey Lykov
    Abstract:

    This study presents airborne in-situ and satellite remote sensing climatologies of Cirrus clouds and humidity. The climatologies serve as a guide to the properties of Cirrus clouds, with the new in-situ data base providing detailed insights into boreal mid-latitudes and the tropics, while the satellite-borne data set offers a global overview. To this end, an extensive, quality checked data archive, the Cirrus Guide II in-situ data base, is created from airborne in-situ measurements during 150 flights in 24 campaigns. The archive contains meteorological parameters, IWC, Nice, Rice, RHice and H2O for each of the flights (IWC: ice water content, Nice: number concentration of ice crystals, Rice: ice crystal mean mass radius, RHice: relative humidity with respect to ice, H2O: water vapor mixing ratio). Depending on the specific parameter, the data base has extended by about a factor of 5–10 compared to the previous studies of Schiller et al. (2008), JGR, and Krämer et al. (2009), ACP. One result of our investigations is, that across all latitudes, the thicker liquid origin Cirrus predominate at lower altitudes, while at higher altitudes the thinner in-situ Cirrus prevail. Further, exemplary investigations of the radiative characteristics of in-situ and liquid origin Cirrus show that the in-situ origin Cirrus only slightly warm the atmosphere, while liquid origin Cirrus have a strong cooling effect. An important step in completing the Cirrus Guide II is the provision of the global Cirrus Nice climatology, derived by means of the retrieval algorithm DARDAR-Nice from ten years of Cirrus remote sensing observations from satellite. The in-situ data base has been used to evaluate and adjust the satellite observations. We found that the global median Nice from satellite observations is almost two times higher than the in-situ median and increases slightly with decreasing temperature. Nice medians of the most frequentl occuring Cirrus sorted by geographical regions are highest in the tropics, followed by austral/boreal mid-latitudes, Antarctica and the Arctic. Since the satellite climatologies enclose the entire spatial and temporal Nice occurrence, we could deduce that half of the Cirrus are located in the lowest, warmest Cirrus layer and contain a significant amount of liquid origin Cirrus. A specific highlight of the study is the in-situ observations of tropical tropopause layer (TTL) Cirrus and humidity in the Asian monsoon anticyclone and the comparison to the surrounding tropics. In the convectively very active Asian monsoon, peak values of Nice and IWC of 30 ppmv and 1000 ppmv are detected around the cold point tropopause (CPT). Above the CPT, ice particles that are convectively injected can locally add a significant amount of water available for exchange with the stratosphere. We found IWCs of up to 8 ppmv in the Asian monsoon in comparison to only 2 ppmv in the surrounding tropics. Also, the highest RHice inside of the clouds as well as in clear sky (120–150 %) are observed around and above the CPT. We attribute this to the high amount of H2O (3–5 ppmv) in comparison to 1.5–3 ppmv in other tropical regions. The supersaturations above the CPT suggest that the water exchange with the stratosphere is 10–20 % higher than expected in regions of weak convective activity and up to about 50 % in the Asian monsoon.

  • ml Cirrus the airborne experiment on natural Cirrus and contrail Cirrus with the high altitude long range research aircraft halo
    Bulletin of the American Meteorological Society, 2017
    Co-Authors: Christiane Voigt, Maxi Boettcher, Armin Afchine, Luca Bugliaro, Ulrich Schumann, Andreas Minikin, Ahmed Abdelmonem, Stephan Borrmann, Bernhard Buchholz, Anja Costa
    Abstract:

    AbstractThe Midlatitude Cirrus experiment (ML-Cirrus) deployed the High Altitude and Long Range Research Aircraft (HALO) to obtain new insights into nucleation, life cycle, and climate impact of natural Cirrus and aircraft-induced contrail Cirrus. Direct observations of Cirrus properties and their variability are still incomplete, currently limiting our understanding of the clouds’ impact on climate. Also, dynamical effects on clouds and feedbacks are not adequately represented in today’s weather prediction models.Here, we present the rationale, objectives, and selected scientific highlights of ML-Cirrus using the G-550 aircraft of the German atmospheric science community. The first combined in situ–remote sensing cloud mission with HALO united state-of-the-art cloud probes, a lidar and novel ice residual, aerosol, trace gas, and radiation instrumentation. The aircraft observations were accompanied by remote sensing from satellite and ground and by numerical simulations.In spring 2014, HALO performed 16 f...

  • the origin of midlatitude ice clouds and the resulting influence on their microphysical properties
    Atmospheric Chemistry and Physics, 2016
    Co-Authors: Anna Luebke, Armin Afchine, Anja Costa, Jensuwe Groos, Jessica Meyer, Christian Rolf, Nicole Spelten, L Avallone
    Abstract:

    Abstract. The radiative role of ice clouds in the atmosphere is known to be important, but uncertainties remain concerning the magnitude and net effects. However, through measurements of the microphysical properties of Cirrus clouds, we can better characterize them, which can ultimately allow for their radiative properties to be more accurately ascertained. Recently, two types of Cirrus clouds differing by formation mechanism and microphysical properties have been classified – in situ and liquid origin Cirrus. In this study, we present observational evidence to show that two distinct types of Cirrus do exist. Airborne, in situ measurements of cloud ice water content (IWC), ice crystal concentration (Nice), and ice crystal size from the 2014 ML-Cirrus campaign provide cloud samples that have been divided according to their origin type. The key features that set liquid origin Cirrus apart from the in situ origin Cirrus are higher frequencies of high IWC ( > 100 ppmv), higher Nice values, and larger ice crystals. A vertical distribution of Nice shows that the in situ origin Cirrus clouds exhibit a median value of around 0.1 cm−3, while the liquid origin concentrations are slightly, but notably higher. The median sizes of the crystals contributing the most mass are less than 200 µm for in situ origin Cirrus, with some of the largest crystals reaching 550 µm in size. The liquid origin Cirrus, on the other hand, were observed to have median diameters greater than 200 µm, and crystals that were up to 750 µm. An examination of these characteristics in relation to each other and their relationship to temperature provides strong evidence that these differences arise from the dynamics and conditions in which the ice crystals formed. Additionally, the existence of these two groups in Cirrus cloud populations may explain why a bimodal distribution in the IWC-temperature relationship has been observed. We hypothesize that the low IWC mode is the result of in situ origin Cirrus and the high IWC mode is the result of liquid origin Cirrus.

  • a microphysics guide to Cirrus clouds part 1 Cirrus types
    Atmospheric Chemistry and Physics, 2015
    Co-Authors: Martina Kramer, Anna Luebke, Armin Afchine, Anja Costa, Jessica Meyer, Christian Rolf, Nicole Spelten, Martin Zoger, J B Smith, R L Herman
    Abstract:

    Abstract. The microphysical and radiative properties of Cirrus clouds continue to be beyond understanding and thus still represent one of the largest uncertainties in the prediction of the Earth's climate (IPCC, 2013). Our study aims to provide a guide to Cirrus microphysics, which is compiled from an extensive set of model simulations, covering the broad range of atmospheric conditions for Cirrus formation and evolution. The model results are portrayed in the same parameter space as field measurements, i.e., in the Ice Water Content-Temperature (IWC-T) parameter space. We validate this Cirrus analysis approach by evaluating Cirrus data sets from 17 aircraft campaigns, conducted in the last 15 years, spending about 94 h in Cirrus over Europe, Australia, Brazil as well as South and North America. Altogether, the approach of this study is to track Cirrus IWC development with temperature by means of model simulations, compare with observations and then assign, to a certain degree, Cirrus microphysics to the observations. Indeed, the field observations show characteristics expected from the simulated Cirrus Guide. For example, high (low) IWCs are found together with high (low) ice crystal concentrations Nice. An important finding from our study is the classification of two types of Cirrus with differing formation mechanisms and microphysical properties: the first Cirrus type forms directly as ice (in situ origin Cirrus) and splits in two subclasses, depending on the prevailing strength of the updraft: in slow updrafts these Cirrus are rather thin with lower IWCs, while in fast updrafts thicker Cirrus with higher IWCs can form. The second type consists predominantly of thick Cirrus originating from mixed phase clouds (i.e., via freezing of liquid droplets – liquid origin Cirrus), which are completely glaciated while lifting to the Cirrus formation temperature region (