A new model to simulate and predict the properties of a large ensemble of contrails as a function of given air traffic and meteorology is described. The model is designed for approximate prediction ...of contrail cirrus cover and analysis of contrail climate impact, e.g. within aviation system optimization processes. The model simulates the full contrail life-cycle. Contrail segments form between waypoints of individual aircraft tracks in sufficiently cold and humid air masses. The initial contrail properties depend on the aircraft. The advection and evolution of the contrails is followed with a Lagrangian Gaussian plume model. Mixing and bulk cloud processes are treated quasi analytically or with an effective numerical scheme. Contrails disappear when the bulk ice content is sublimating or precipitating. The model has been implemented in a "Contrail Cirrus Prediction Tool" (CoCiP). This paper describes the model assumptions, the equations for individual contrails, and the analysis-method for contrail-cirrus cover derived from the optical depth of the ensemble of contrails and background cirrus. The model has been applied for a case study and compared to the results of other models and in-situ contrail measurements. The simple model reproduces a considerable part of observed contrail properties. Mid-aged contrails provide the largest contributions to the product of optical depth and contrail width, important for climate impact.
Aviation alters the composition of the atmosphere globally and can thus drive climate change and ozone depletion. The last major international assessment of these impacts was made by the ...Intergovernmental Panel on Climate Change (IPCC) in 1999. Here, a comprehensive updated assessment of aviation is provided. Scientific advances since the 1999 assessment have reduced key uncertainties, sharpening the quantitative evaluation, yet the basic conclusions remain the same. The climate impact of aviation is driven by long-term impacts from CO
2 emissions and shorter-term impacts from non-CO
2 emissions and effects, which include the emissions of water vapour, particles and nitrogen oxides (NO
x
). The present-day radiative forcing from aviation (2005) is estimated to be 55 mW m
−2 (excluding cirrus cloud enhancement), which represents some 3.5% (range 1.3–10%, 90% likelihood range) of current anthropogenic forcing, or 78 mW m
−2 including cirrus cloud enhancement, representing 4.9% of current forcing (range 2–14%, 90% likelihood range). According to two SRES-compatible scenarios, future forcings may increase by factors of 3–4 over 2000 levels, in 2050. The effects of aviation emissions of CO
2 on global mean surface temperature last for many hundreds of years (in common with other sources), whilst its non-CO
2 effects on temperature last for decades. Much progress has been made in the last ten years on characterizing emissions, although major uncertainties remain over the nature of particles. Emissions of NO
x
result in production of ozone, a climate warming gas, and the reduction of ambient methane (a cooling effect) although the overall balance is warming, based upon current understanding. These NO
x
emissions from current subsonic aviation do not appear to deplete stratospheric ozone. Despite the progress made on modelling aviation's impacts on tropospheric chemistry, there remains a significant spread in model results. The knowledge of aviation's impacts on cloudiness has also improved: a limited number of studies have demonstrated an increase in cirrus cloud attributable to aviation although the magnitude varies: however, these trend analyses may be impacted by satellite artefacts. The effect of aviation particles on clouds (with and without contrails) may give rise to either a positive forcing or a negative forcing: the modelling and the underlying processes are highly uncertain, although the overall effect of contrails and enhanced cloudiness is considered to be a positive forcing and could be substantial, compared with other effects. The debate over quantification of aviation impacts has also progressed towards studying potential mitigation and the technological and atmospheric tradeoffs. Current studies are still relatively immature and more work is required to determine optimal technological development paths, which is an aspect that atmospheric science has much to contribute. In terms of alternative fuels, liquid hydrogen represents a possibility and may reduce some of aviation's impacts on climate if the fuel is produced in a carbon-neutral way: such fuel is unlikely to be utilized until a ‘hydrogen economy’ develops. The introduction of biofuels as a means of reducing CO
2 impacts represents a future possibility. However, even over and above land-use concerns and greenhouse gas budget issues, aviation fuels require strict adherence to safety standards and thus require extra processing compared with biofuels destined for other sectors, where the uptake of such fuel may be more beneficial in the first instance.
The COVID‐19 pandemic led to a 72% reduction of air traffic over Europe in March–August 2020 compared to 2019. Modeled contrail cover declined similarly, and computed mean instantaneous radiative ...contrail forcing dropped regionally by up to 0.7 W m−2. Here, model predictions of cirrus optical thickness and the top‐of‐atmosphere outgoing longwave and reflected shortwave irradiances are tested by comparison to Meteosat‐SEVIRI‐derived data. The agreement between observations and modeled data is slightly better when modeled contrail cirrus contributions are included. The spatial distributions and diurnal cycles of the differences in these data between 2019 and 2020 are partially caused by differences in atmospheric and surface conditions, particularly for solar radiation in the spring of 2020. Aviation signals become discernible in the observed differences of these data between 2019 and 2020 when subtracting numerical weather prediction model results that approximate the atmosphere and surface conditions without contrails.
Plain Language Summary
Aircraft flying in cold and humid air masses induce contrails which warm the Earth‐atmosphere system by reducing the terrestrial radiation out into space and cool by increasing the Earth’s albedo. Previous studies found that the warming effects dominate and that contrails may contribute most of the present radiative forcing of climate change induced by aviation. The COVID‐19 pandemic led to a worldwide and long‐duration reduction of air traffic. This paper compares model predictions and satellite‐observed cirrus properties and irradiances over Europe for 6 months in 2019 and 2020. The models account for changes in the atmosphere and at the Earth’s surface in the two half‐years. Model and observation results show about 90% correlation and 20% mean normalized deviations. The agreement between observed and modeled optical cirrus thickness and terrestrial irradiances improves slightly when the modeled contrail cirrus contributions are included. Solar radiation changes show a larger variability because of large changes in the lower atmosphere and at the Earth surface. Since worldwide traffic activity has stayed at low levels after August 2020, the comparisons may be extended. Further model studies, including the effects of other emissions, are needed for a more comprehensive understanding of the observed changes.
Key Points
Air traffic reduction during the COVID‐19 pandemic is used for testing aviation contrail cirrus and related radiative forcing modeling
Cirrus optical depth and top‐of‐atmosphere irradiances from satellite observations and model results show reasonable correlations
Aviation contrail signatures are identifiable in spite of strongly different atmosphere and surface conditions in 2019 and 2020
The uptake of water by contrails in ice-supersaturated air and the release of water after ice particle advection and sedimentation dehydrates the atmosphere at flight levels and redistributes ...humidity mainly to lower levels. The dehydration is investigated by coupling a plume-scale contrail model with a global aerosol-climate model. The contrail model simulates all the individual contrails forming from global air traffic for meteorological conditions as defined by the climate model. The computed contrail cirrus properties compare reasonably with theoretical concepts and observations. The mass of water in aged contrails may exceed 106 times the mass of water emitted from aircraft. Many of the ice particles sediment and release water in the troposphere, on average 700 m below the mean flight levels. Simulations with and without coupling are compared. The drying at contrail levels causes thinner and longer-lived contrails with about 15 % reduced contrail radiative forcing (RF). The reduced RF from contrails is on the order of 0.06 W m-2, slightly larger than estimated earlier because of higher soot emissions. For normal traffic, the RF from dehydration is small compared to interannual variability. A case with emissions increased by 100 times is used to overcome statistical uncertainty. The contrails impact the entire hydrological cycle in the atmosphere by reducing the total water column and the cover by high- and low-level clouds. For normal traffic, the dehydration changes contrail RF by positive shortwave and negative longwave contributions on the order of 0.04 W m-2, with a small negative net RF. The total net RF from contrails and dehydration remains within the range of previous estimates.
The April–May, 2010 volcanic eruptions of Eyjafjallajökull, Iceland caused significant economic and social disruption in Europe whilst state of the art measurements and ash dispersion forecasts were ...heavily criticized by the aviation industry. Here we demonstrate for the first time that large improvements can be made in quantitative predictions of the fate of volcanic ash emissions, by using an inversion scheme that couples a priori source information and the output of a Lagrangian dispersion model with satellite data to estimate the volcanic ash source strength as a function of altitude and time. From the inversion, we obtain a total fine ash emission of the eruption of 8.3 ± 4.2 Tg for particles in the size range of 2.8–28 μm diameter. We evaluate the results of our model results with a posteriori ash emissions using independent ground-based, airborne and space-borne measurements both in case studies and statistically. Subsequently, we estimate the area over Europe affected by volcanic ash above certain concentration thresholds relevant for the aviation industry. We find that during three episodes in April and May, volcanic ash concentrations at some altitude in the atmosphere exceeded the limits for the "Normal" flying zone in up to 14 % (6–16 %), 2 % (1–3 %) and 7 % (4–11 %), respectively, of the European area. For a limit of 2 mg m−3 only two episodes with fractions of 1.5 % (0.2–2.8 %) and 0.9 % (0.1–1.6 %) occurred, while the current "No-Fly" zone criterion of 4 mg m−3 was rarely exceeded. Our results have important ramifications for determining air space closures and for real-time quantitative estimations of ash concentrations. Furthermore, the general nature of our method yields better constraints on the distribution and fate of volcanic ash in the Earth system.
This paper is one of a series addressing the need for simple, yet accurate, methods for the estimation of cruise fuel burn and other important aircraft performance parameters. Here, a previously ...published, constant Reynolds number model for turbofan-powered, civil transport aircraft is extended to include Reynolds number effects. Provided the variation of temperature with pressure is known, the method is applicable to flight in any atmospheric conditions. For a given aircraft, cruising in a given atmosphere, there is a single Mach number and Flight Level pair, at which the fuel burn per unit distance travelled through the air has an absolute minimum value. Both these quantities depend upon the Reynolds number, which, in turn, depends upon the aircraft weight and the atmospheric vertical temperature profile. Simple, explicit expressions are developed for all parameters at the optimum condition. These are shown to be in close agreement with numerical solutions of the governing equations. It is found that typical operational mass and temperature profile variations can change cruise fuel burn rate by several percent. In the International Standard Atmosphere, when the speed and altitude deviate from their optimum values, the fuel burn penalty is reduced slightly relative to the constant Reynolds number case. By way of example, the method is used to estimate the minimum fuel, speed-versus-height trajectory for cruise in a realistic atmosphere. For each aircraft, cruise fuel burn is found to be governed by six independent parameters. All are constants. Two are simple, involving only size and weight, whereas four are complex and must be determined by either theoretical, or empirical, means. The estimation of these quantities will be considered in Part 2.
A new parameterized analytical model is presented to compute the instantaneous radiative forcing (RF) at the top of the atmosphere (TOA) produced by an additional thin contrail cirrus layer (called ...“contrail” below). The model calculates the RF using as input the outgoing longwave radiation and reflected solar radiation values atTOAfor a contrail-free atmosphere, so that the model is applicable for both cloud-free and cloudy ambient atmospheres. Additional input includes the contrail temperature, contrail optical depth (at 550 nm), effective particle radius, particle habit, solar zenith angle, and the optical depth of cirrus above the contrail layer. The model parameters (5 for longwave and 10 for shortwave) are determined from least squares fits to calculations from the “libRadtran” radiative transfer model over a wide range of atmospheric and surface conditions. The correlation coefficient between model and calculations is larger than 98%. The analytical model is compared with published results, including a 1-yr simulation of global RF, and is found to agree well with previous studies. The fast analytical model is part of a larger modeling system to simulate contrail life cycles (“CoCiP”) and can allow for the rapid simulation of contrail cirrus RF over a wide range of meteorological conditions and for a given size-dependent habit mixture. Ambient clouds are shown to have large local impact on the net RF of contrails. Net RF of contrails may both increase and decrease and even change sign in the presence of higher-level cirrus, depending on solar zenith angle.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A simple yet physically comprehensive and accurate method for the estimation of the cruise fuel burn rate of turbofan powered transport aircraft operating in a general atmosphere was developed in ...part 1. The method is built on previously published work showing that suitable normalisation reduces the governing relations to a set of near-universal curves. However, to apply the method to a specific aircraft, values must be assigned to six independent parameters and the more accurate these values are the more accurate the estimates will be. Unfortunately, some of these parameters rarely appear in the public domain. Consequently, a scheme for their estimation is developed herein using basic aerodynamic theory and data correlations. In addition, the basic method is extended to provide estimates for cruise lift-to-drag ratio, engine thrust and engine overall efficiency. This step requires the introduction of two more independent parameters, increasing the total number from six to eight. An error estimate and sensitivity analysis indicates that, in the aircraft’s normal operating range and using the present results, estimates of fuel burn rate are expected to be in error by no more than 5% in the majority of cases. Initial estimates of the characteristic parameters have been generated for 53 aircraft types and engine combinations and a table is provided.
The eruption of the Eyjafjallajökull volcano, Iceland, in April and May 2010 caused unprecedented disruptions of European air traffic showing that timely monitoring of volcanic ash and SO2 dispersion ...as well as the corresponding plume heights are important for aviation safety. This paper describes the observations of SO2 and BrO columns in the eruption plume and the determination of the SO2 plume height using the GOME‐2 satellite instrument. During the eruptive period in May 2010, SO2 total columns of up to ∼20 DU and BrO columns of ∼7.7 × 1013 molec/cm2 were detected. The BrO/SO2 ratio estimated from the GOME‐2 observations of the Eyjafjallajökull eruption varies from 1.1 × 10−4 to 2.1 × 10−4. The SO2 plume heights estimated from the GOME‐2 observations on 5 May range from 8–13 km and mostly agree within 1–3 km with visual observations, radar data and modeling results. Furthermore, the GOME‐2 SO2 observations are compared with in situ measurements of the DLR Falcon aircraft on 17 and 18 May 2010 and with Brewer instruments at Valentia, Ireland and Hohenpeissenberg, Germany. The SO2 columns derived from the Falcon profile measurements range from 0.6–4.7 DU and the comparison with the GOME‐2 measurements shows a good agreement, mainly within 1 DU. The Brewer observations at Hohenpeissenberg also agree well with the GOME‐2 measurements with a daily average SO2 column of ∼1.3 DU during the overpass of the SO2 cloud on 18 May, whereas the Brewer instrument at Valentia shows up to 50% higher SO2 columns (∼8 DU) on 11 May.
Key Points
SO2 and BrO in the eruption plume of Eyjafjallajokull using GOME‐2
Direct retreival of the SO2 plume height from GOME‐2 measurements
Comparison of GOME‐2 data with model simulations, Falcon and Brewer observations
The investigation of the impact of aircraft parameters on contrail properties helps to better understand the climate impact from aviation. Yet, in observations, it is a challenge to separate aircraft ...and meteorological influences on contrail formation. During the CONCERT campaign in November 2008, contrails from 3 Airbus passenger aircraft of types A319-111, A340-311 and A380-841 were probed at cruise under similar meteorological conditions with in situ instruments on board DLR research aircraft Falcon. Within the 2 min-old contrails detected near ice saturation, we find similar effective diameters Deff (5.2–5.9 μm), but differences in particle number densities nice (162–235 cm−3) and in vertical contrail extensions (120–290 m), resulting in large differences in contrail optical depths τ at 550 nm (0.25–0.94). Hence larger aircraft produce optically thicker contrails. Based on the observations, we apply the EULAG-LCM model with explicit ice microphysics and, in addition, the Contrail and Cirrus Prediction (CoCiP) model to calculate the aircraft type impact on young contrails under identical meteorological conditions. The observed increase in τ for heavier aircraft is confirmed by the models, yet for generally smaller τ. CoCiP model results suggest that the aircraft dependence of climate-relevant contrail properties persists during contrail lifetime, adding importance to aircraft-dependent model initialization. We finally derive an analytical relationship between contrail, aircraft and meteorological parameters. Near ice saturation, contrail width × τ scales linearly with the fuel flow rate, as confirmed by observations. For higher relative humidity with respect to ice (RHI), the analytical relationship suggests a non-linear increase in the form (RHI-12/3. Summarized, our combined results could help to more accurately assess the climate impact from aviation using an aircraft-dependent contrail parameterization.
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