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Der Beitrag des Flugverkehrs zum Tagesgang der Zirrenbedeckung und der ausgehenden langwelligen Strahlung über dem Nordatlantischen Flugkorridor
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In this study, a substantially improved version of the Meteosat cirrus detection algorithm (MeCiDA2) will be presented, which now allows application to the full earth disc visible by the Meteosat satellite. As cirrus clouds have an influence on the radiation budget of the earth, their optical properties and their global coverage has to be monitored at the global scale using instruments aboard geostationary satellites. Since MeCiDA was optimised for the area of Europe only, various changes were necessary to handle the variable conditions found over the full Meteosat disc. Required changes include the consideration of the viewing angle dependency and of the sensitivity of the 9.7 μm channel to the ozone column. To this end, a correction is implemented that minimises the influence of the variability of the stratospheric ozone. The evaluation of the proposed improvements is carried out by using MeCiDA applied to MODIS (moderate resolution imaging spectrometer) data to address viewing angle-dependent cirrus detection, and by additionally comparing it to the cloud optical properties MOD06 cirrus product. The new MeCiDA version detects less cirrus than the original one for latitudes larger than 40°, but almost the same amount elsewhere. MeCiDA's version for MODIS is more sensitive than that for SEVIRI (spinning enhanced visible and infrared imager) with cirrus occurrences higher by 10%, and the new MeCiDA provides almost the same cirrus coverage (±0.1) as given by the cloud phase optical properties from MODIS for latitudes smaller than 50°. Finally, the influence of sub-pixel clouds on the SEVIRI cirrus detection has been examined: more than 60% of the undetected SEVIRI cirrus pixels have a cirrus coverage smaller than 0.5.
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.
Rising global air traffic and its associated contrails have the potential for affecting climate via radiative forcing. Current estimates of contrail climate effects are based on coverage by linear contrails that do not account for spreading and, therefore, represent the minimum impact. The maximum radiative impact is estimated by assuming that long-term trends in cirrus coverage are due entirely to air traffic in areas where humidity is relatively constant. Surface observations from 1971 to 1995 show that cirrus increased significantly over the northern oceans and the United States while decreasing over other land areas except over western Europe where cirrus coverage was relatively constant. The surface observations are consistent with satellite-derived trends over most areas. Land cirrus trends are positively correlated with upper-tropospheric (300 hPa) humidity (UTH), derived from the National Centers for Environmental Prediction (NCEP) analyses, except over the United States and western Europe where air traffic is heaviest. Over oceans, the cirrus trends are negatively correlated with the NCEP relative humidity suggesting some large uncertainties in the maritime UTH. The NCEP UTH decreased dramatically over Europe while remaining relatively steady over the United States, thereby permitting an assessment of the cirrus-contrail relationship over the United States. Seasonal cirrus changes over the United States are generally consistent with the annual cycle of contrail coverage and frequency lending additional evidence to the role of contrails in the observed trend. It is concluded that the U.S. cirrus trends are most likely due to air traffic. The cirrus increase is a factor of 1.8 greater than that expected from current estimates of linear contrail coverage suggesting that a spreading factor of the same magnitude can be used to estimate the maximum effect of the contrails. From the U.S. results and using mean contrail optical depths of 0.15 and 0.25, the maximum contrail-cirrus global radiative forcing is estimated to be 0.006-0.025 W m-2 depending on the radiative forcing model. Using results from a general circulation model simulation of contrails, the cirrus trends over the United States are estimated to cause a tropospheric warming of 0.2°-0.3°C decade-1, a range that includes the observed tropospheric temperature trend of 0.27°C decade-1 between 1975 and 1994. The magnitude of the estimated surface temperature change and the seasonal variations of the estimated temperature trends are also in good agreement with the corresponding observations.
The Japanese Advanced Meteorological Imager (JAMI) introduces next
generation technology geosynchronous earth orbit (GEO) imagers for
operational meteorological remote sensing. Raytheon Santa Barbara Remote
Sensing is building JAMI for Space Systems/Loral as the imager subsystem
for Japan's MTSAT-1R system. JAMI represents the best balance between
heritage and newer space-qualified technology and meets all Japan
Ministry of Transport MTSAT requirements from beginning to end of life
with considerable margin, using a simple, inherently low risk design.
The advanced technology built into this imager benefits operational
meteorological imaging for Japan, East Asia and Australia by enabling
significantly better radiometric sensitivity and absolute accuracy,
higher spatial resolution and faster full disk coverage times than
available from current GEO imagers. JAMI is on schedule for an on time
or early delivery to Space Systems/Loral.
Understanding the role of contrails in the Earth's radiation budget
requires an accurate characterization of their macrophysical and
microphysical properties, such as cloud top temperature, optical depth,
and effective particle size. These properties are derived from 2006
MODerate-resolution Imaging Spectroradiometer data over the Northern
Hemisphere using a bi-spectral, infrared-only retrieval technique.
Contrail temperature is estimated using a quadratic relationship of
flight track pressure with latitude. The results reveal distinct
seasonal trends in contrail microphysical properties, with slightly
greater mean optical depths and slightly smaller particle sizes during
summer. The average contrail optical depth and particle effective
diameter are 0.216 and 35.7 µm, respectively. Although fewer
contrails occurred at night, there are no appreciable diurnal
differences in their retrieved properties. These results should help to
fill the gap in our knowledge of contrail properties and will be
valuable for model validation.
The physical and optical properties of persistent contrails were studied
with the measurements made by the Moderate Resolution Imaging
Spectroradiometer (MODIS) and the Cloud-Aerosol Lidar and Infrared
Pathfinder Satellite Observations (CALIPSO) lidar. MODIS data were used
to determine the contrail locations on the basis of their artificial
shapes easily distinguished from natural cirrus, and the so-identified
contrails were analyzed with collocated CALIPSO lidar data. Statistics
of the geography, geometry, meteorology, and optical properties are
reported for approximately 3400 persistent contrails observed over North
America, the North Atlantic Ocean, and Europe. The majority of the
detected contrails appear in ice-supersaturated air with temperatures
lower than -40°C. On average, contrails have significantly larger
backscattering coefficients and slightly higher linear depolarization
ratios (LDRs) than neighboring cirrus clouds. Depolarization tends to be
strong when ice crystals are small, and LDR is approximately 0.4-0.45
for young contrails and contrail cores. The mean LDR for the detected
contrails increases with decreasing temperature and is not strongly
dependent on the lidar pointing angle. The backscattering properties
suggest that contrails are primarily composed of small, randomly
oriented ice crystals but may also contain a few horizontally oriented
plates. Most contrails are optically thin with a mean (median) optical
thickness of approximately 0.19 (0.14); however, optically thicker
contrails do exist and tend to occur in warmer and more humid ambient
air. The mean value and range of the observed LDR data are consistent
with theoretical predictions based on a mixture of nonspherical ice
crystals randomly oriented in the atmosphere.
A new Rapid Retrieval of upwelling fluxes from MSG/SEVIRI (RRUMS) is
presented. It has been developed to observe the top-of-atmosphere
irradiances of small scale and rapidly changing features that are not
sufficiently resolved by specific Earth radiation budget sensors. Our
retrieval takes advantage of the spatial and temporal resolution of
MSG/SEVIRI and provides outgoing longwave and reflected shortwave
radiation only by means of a combination of SEVIRI channels. The
longwave retrieval is based on a simple linear combination of brightness
temperatures from the SEVIRI infrared channels. Two shortwave retrievals
are presented and discussed: the first one based on a multilinear
parameterisation and the second one based on a neural network. The
neural network method is shown to be slightly more accurate and simpler
to apply for the desired purpose. Both LW and SW algorithms have been
validated by comparing their results with CERES and GERB irradiance
observations. While being less accurate than their dedicated
counterparts, the SEVIRI-based methods have two major advantages
compared to CERES and GERB: their higher spatial resolution and the
better temporal resolution. With our retrievals it is possible to
observe the radiative effect of small-scale features such as cumulus
clouds, cirrus clouds, or aircraft contrails. The spatial resolution of
SEVIRI is 3 km × 3 km in the sub-satellite point, remarkably
better than that of CERES (20 km) or GERB (45 km). The temporal
resolution is 15 min (5 min in the rapid-scan mode), the same as GERB,
but significantly better than that of CERES which, being on board of a
polar orbiting satellite, has a temporal resolution as low as 2
overpasses per day.
EUMETSAT and ESA initiated in 2000 joint preparatory activities for the
formulation and definition of the Meteosat Third Generation (MTG)
geostationary system, to ensure continuity and improvement of current
Meteosat Second Generation (MSG) services. MTG will become the backbone
of the European operational meteorological applications taking the relay
from MSG by 2017, and warranting the continuation of the earth imagery
mission supported by the Spin Enhanced Visible and Infrared Imager
(SEVIRI). The early program definition phases were devoted to the
discussion and consolidation of end user requirements and their
priorities in meteorology fields as Nowcasting and Very Short Term
Weather Forecasting (NWC), Medium/Short Range global and regional
Numerical Weather Prediction (NWP), Climate and Air Composition
Monitoring and the identification of the relevant observation
techniques. In the system conceptualization process, the following
missions have been analyzed: • Full Disc High Spectral resolution
Imagery (FDHSI) • High Resolution and Fast Imagery (HRFI) •
Lightning detection Mission (LI) • IR Sounding Mission (IRS) •
UV-VIS-NIR Sounding Mission as a payload complement (UVN). After
pre-phase A mission studies (2003-2006), where preliminary instrument
concepts were investigated allowing the consolidation of the most
critical and demanding technical requirements, phase A studies were
launched at the beginning of February (2007-2008) addressing both the
space segment system feasibility and ground and operations programmatic
aspects. The space segment, phase A level, studies covered the entire
suite of optical instruments identified in the preliminary assessments
including: 1) a flexible combined imager for both FDHSI and HRFI
missions; 2) a Fourier Transform Spectrometer for IRS observations; and
3) a lightning detector sensor. The study of concepts and implementation
of the UVN mission are covered by the efforts of ESA and the European
Union (EU) in the framework of the Global Monitoring for Environment and
Security (GMES) Sentinel 4 program. This paper provides an overview of
the outcome of the MTG System analyses at the end of phase A confirming
its technical feasibility, the key characteristics of the intended
missions, and the progress accomplished in the definition of the
satellite optical payloads.
This paper articulates trends in the environmental im- pact of military aviation between 1960 and 2000. The fo- cus is on community noise, local air quality, and global climate impacts and the discussion is restricted to fixed- wing aircraft. Comparisons are made to trends within the commercial air transport industry. The unique features of military aircraft technology and operations responsible for the differences in environmental impacts are described. The discussion also considers the effects of environmental restrictions on the deployment and combat readiness of military aviation services. Regulations designed to mitigate environmental impacts from military and civil aviation are also reviewed. The analysis shows that military aviation has been responsible for a small and decreasing fraction of total fossil fuel use in the United States. Further, when averaged nationally, contributions to local air quality impacts and community noise have decreased over the period consid- ered. These trends are a result of historical reductions in fleet sizes and number of operations. However, since base closures were largely responsible for these reductions, the impacts at any given installation may not reflect overall trends. Community noise and air quality are expected to be a growing concern for military aviation due to increasing urbanization, increasing public and regulatory attention, and use of training spaces for larger, multi-service opera- tions involving longer range, higher speed weapon sys- tems.
An update is provided on the Earth's global annual mean energy budget in the light of new observations and analyses. In 1997, Kiehl and Trenberth provided a review of past estimates and performed a number of radiative computations to better establish the role of clouds and various greenhouse gases in the overall radiative energy flows, with top-of-atmosphere(TOA) values constrained by Earth Radiation Budget Experiment values from 1985 to 1989, when the TOA values were approximately in balance. The Clouds and the Earth's Radiant Energy System (CERES) measurements from March 2000 to May 2004 are used at TOA but adjusted to an estimated imbalance from the enhanced greenhouse effect of 0.9 W m(-2). Revised estimates of surface turbulent fluxes are made based on various sources. The partitioning of solar radiation in the atmosphere is based in part on the International Satellite Cloud Climatology Project (ISCCP) FD computations that utilize the global ISCCP cloud data every 3 h, and also accounts for increased atmospheric absorption by water vapor and aerosols. Surface upward longwave radiation is adjusted to account for spatial and temporal variability. A lack of closure in the energy balance at the surface is accommodated by making modest changes to surface fluxes, with the downward longwave radiation as the main residual to ensure a balance. Values are also presented for the land and ocean domains that include a net transport of energy from ocean to land of 2.2 petawatts (PW) of which 3.2 PW is from moisture (latent energy) transport, while net dry static energy transport is from land to ocean. Evaluations of atmospheric re-analyses reveal substantial biases.
Three contrail systems were analyzed with geostationary satellite data to document the conversion of the contrails to cirrus clouds. Two unique contrails, a pair of figure eights and a NASA DC-8 oval, were tracked for more than 7 hours. A cluster of contrails from commercial aircraft lasted over 17 hours. The figure eights produced a cirrus cloud having a maximum extent of 12,000 km²; the commercial cluster reached an area of ∼35,000 km². The contrail-cirrus were thin with optical depths between 0.2 and 0.5. In all cases, cloud particle size increased as the contrails developed into cirrus clouds. The climatic impact of contrails will be greater than would be estimated if only linear contrails, those typically observed in satellite imagery, are considered. Additional research is required to obtain reliable statistics on contrail growth and lifetime.
Widespread persistent contrails over the western Great Lakes during 9 October 2000 were examined using commercial flight data, coincident meteorological data, and satellite remote sensing data from several platforms. The data were analyzed to determine the atmospheric conditions under which the contrails formed and to measure several physical properties of the contrails, including areal coverage, spreading rates, fall speeds, and optical properties. Most of the contrails were located between 10.6 and 11.8 km in atmospheric conditions consistent with a modified form of the Appleman contrail formation theory. However, the Rapid Update Cycle-2 analyses have a dry bias in the upper-tropospheric relative humidity with respect to ice (RHI), as indicated by persistent contrail generation during the outbreak where RHI 85%. The model analyses show that synoptic-scale vertical velocities affect the formation of persistent contrails. Areal coverage by linear contrails peaked at 30000 km2, but the maximum contrail-generated cirrus coverage was over twice as large. Contrail spreading rates averaged around 2.7 km h-1, and the contrails were visible in the 4-km Geostationary Operational Environmental Satellite (GOES) imagery approximately 1 h after formation. Contrail fall speed estimates were between 0.00 and 0.045 m s-1 based on observed contrail advection rates. Optical depth measurements ranged from 0.1 to 0.6, with consistent differences between remote sensing methods. Contrail formation density was roughly correlated with air traffic density after the effects of competing cloud coverage, humidity, and vertical velocity were considered. Improved tropospheric humidity measurements are needed for realistic simulations of contrail and cirrus development.
This work examines changes in cirrus cloud cover in possible association with aviation activities at congested air corridors. The analysis is based on the latest version of the International Satellite Cloud Climatology Project D2 data set and covers the period 1984&ndash1998. Over areas with heavy air traffic, the effect of large-scale modes of natural climate variability such as ENSO, QBO and NAO as well as the possible influence of the tropopause variability, were first removed from the cloud data set in order to calculate long-term changes of observed cirrus cloudiness. The results show increasing trends in cirrus cloud coverage, between 1984 and 1998, over the high air traffic corridors of North America, North Atlantic and Europe, which in the summertime only over the North Atlantic are statistically significant at the 99.5% confidence level (2.6% per decade). In wintertime however, statistically significant changes at the 95% confidence level are found over North America, amounting to +2.1% per decade. Statistically significant increases at the 95% confidence level are also found for the annual mean cirrus cloud coverage over the North Atlantic air corridor (1.2% per decade). Over adjacent locations with lower air traffic, the calculated trends are statistically insignificant and in most cases negative both during winter and summer in regions studied. Moreover, it is shown that the longitudinal distribution of decadal changes in cirrus cloudiness along the latitude belt centered at the North Atlantic air corridor, parallels the spatial distribution of fuel consumption from highflying air traffic, providing an independent test of possible impact of aviation on contrail cirrus formation. Results from this study are compared with other studies and different periods of records and it appears as evidenced in this and in earlier studies that there exists general agreement on the aviation effect on high cloud trends.
Persistent contrails are believed to currently have a relatively small but significant positive radiative forcing on climate. With air travel predicted to continue its rapid growth over the coming years, the contrail warming effect on climate is expected to increase. Nevertheless, there remains a high level of uncertainty in the current estimates of contrail radiative forcing. Contrail formation depends mostly on the aircraft flying in cold and moist enough air masses. Most studies to date have relied on simple parameterizations using averaged meteorological conditions. In this paper we take into account the short-term variability in background cloudiness by developing an on-line contrail parameterization for the UK Met Office climate model. With this parameterization, we estimate that for the air traffic of year 2002 the global mean annual linear contrail coverage was approximately 0.11%. Assuming a global mean contrail optical depth of 0.2 or smaller and assuming hexagonal ice crystals, the corresponding contrail radiative forcing was calculated to be less than 10 mW m-2 in all-sky conditions. We find that the natural cloud masking effect on contrails may be significantly higher than previously believed. This new result is explained by the fact that contrails seem to preferentially form in cloudy conditions, which ameliorates their overall climate impact by approximately 40%.
The low-temperature aerosol and cloud chamber AIDA (Aerosol Interactions and Dynamics in the Atmosphere) of Forschungszentrum Karlsruhe was used to investigate the effect of sulfuric acid coating on the ice nucleation efficiency of soot aerosol particles from a spark discharge generator. The uncoated (sulfuric acid-coated) soot aerosol showed a nearly lognormal size distribution with number concentrations of 300-5000 cm-3 (2500-56,000 cm-3), count median diameters of 70-140 nm (90-200 nm), and geometric standard deviation of 1.3-1.4 (1.5-1.6). The volume fraction of the sulfuric acid coating to the total aerosol volume concentration ranged from 21 to 81%. Ice activation was investigated in dynamic expansion experiments simulating cloud cooling rates between about -0.6 and -3.5 K min-1. At temperatures between 186 and ~235 K, uncoated soot particles acted as deposition nuclei at very low ice saturation ratios between 1.1 and 1.3. Above 235 K, ice nucleation only occurred after approaching liquid saturation. Coating with sulfuric acid significantly increased the ice nucleation thresholds of soot aerosol to saturation ratios increasing from ~1.3 at 230 K to ~1.5 at 185 K. This immersion mode of freezing nucleates ice well below the thresholds for homogeneous freezing of pure sulfuric acid solution droplets measured in previous AIDA experiments. A case study indicated that in contrast to the homogeneous freezing the nucleation rate of the immersion freezing mechanism depends only weakly on relative humidity and thereby the solute concentration. These results show that it is important to know the mixing state of soot and sulfuric acid aerosol particles in order to properly assess their role in cirrus formation.
The frequency of cloud detection and the frequency with which these clouds are found in the upper troposphere have been extracted from NOAA High Resolution Infrared Radiometer Sounder (HIRS) polar-orbiting satellite data from 1979 to 2001. The HIRS/2 sensor was flown on nine satellites from the Television Infrared Observation Satellite-Next Generation (TIROS-N) through NOAA-14, forming a 22-yr record. Carbon dioxide slicing was used to infer cloud amount and height. Trends in cloud cover and high-cloud frequency were found to be small in these data. High clouds show a small but statistically significant increase in the Tropics and the Northern Hemisphere. The HIRS analysis contrasts with the International Satellite Cloud Climatology Project (ISCCP), which shows a decrease in both total cloud cover and high clouds during most of this period.
The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) is a two-wavelength polarization lidar that performs global profiling of aerosols and clouds in the troposphere and lower stratosphere. CALIOP is the primary instrument on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite, which has flown in formation with the NASA A-train constellation of satellites since May 2006. The global, multiyear dataset obtained from CALIOP provides a new view of the earth's atmosphere and will lead to an improved understanding of the role of aerosols and clouds in the climate system. A suite of algorithms has been developed to identify aerosol and cloud layers and to retrieve a variety of optical and microphysical properties. CALIOP represents a significant advance over previous space lidars, and the algorithms that have been developed have many innovative aspects to take advantage of its capabilities. This paper provides a brief overview of the CALIPSO mission, the CALIOP instrument and data products, and an overview of the algorithms used to produce these data products.
High-level cirrus clouds can evolve¹, ² from the condensation trails of aircraft, which form as the mixture of warm, humid exhaust gases and colder, drier air exceeds water saturation³. In addition, the particles in exhaust plumes from aircraft may allow ice nucleation at lower supersaturations than those required under natural conditions⁴. This mechanism is sensitive to environmental conditions, but may occur downstream of the exhaust aerosol source regions. Here I show that cirrus clouds increased in occurrence and coverage in the main air-traffic flight corridors between 1982 and 1991.
ERA-Interim is the latest global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). The ERA-Interim project was conducted in part to prepare for a new atmospheric reanalysis to replace ERA-40, which will extend back to the early part of the twentieth century. This article describes the forecast model, data assimilation method, and input datasets used to produce ERA-Interim, and discusses the performance of the system. Special emphasis is placed on various difficulties encountered in the production of ERA-40, including the representation of the hydrological cycle, the quality of the stratospheric circulation, and the consistency in time of the reanalysed fields. We provide evidence for substantial improvements in each of these aspects. We also identify areas where further work is needed and describe opportunities and objectives for future reanalysis projects at ECMWF.
The CM-SAF is aiming at the provision of satellite-derived geophysical parameters suited for climate monitoring. After a five year development phase the CM-SAF entered the so called Initial Operations Phase (IOP) in January 2004 which will lead to the full operations phase expected for early 2007. CM-SAF produces a climatology of cloud parameters (e.g. cloud fraction, cloud top temperature, etc.), surface radiation fluxes and surface albedo, radiation fluxes at the top of the atmosphere, and atmospheric water vapor. The products are currently derived from data of instruments on-board the polar orbiting NOAA satellites and the geostationary Meteosat Second Generation (MSG) satellite. During the IOP data from the instruments on-board the Metop satellite will be integrated into the products. As the CM-SAF has currently only a mandate for regional climate monitoring the area covers Europe and part of the North Atlantic Ocean. The coverage will be extended to the whole MSG disk as well as the Inner Arctic area during the IOP. Operational production has started in January 2005 using NOAA data for cloud and surface radiation products as well as Meteosat 8 and CERES data for top of atmosphere radiation fluxes. The water vapor product consists of total as well as layered precipitable water constructed from the ATOVS system and SEVIRI estimates and will be operational available in late 2005.
Validation of cloud properties retrieved from
passive spaceborne imagers is essential for cloud and climate applications but complicated due to the large differences in scale and observation geometry between the satellite footprint and the independent ground based or airborne observations. Here we illustrate and demonstrate an alternative approach: starting from the output of the COSMOEU weather model of the German Weather Service realistic three-dimensional cloud structures at a spatial scale of 2.33 km are produced by statistical downscaling and microphysical
properties are associated to them. The resulting data
sets are used as input to the one-dimensional radiative transfer model libRadtran to simulate radiance observations for all eleven low resolution channels of MET-8/SEVIRI. At this point, both cloud properties and satellite radiances are known such that cloud property retrieval results can be tested and
tuned against the objective input “truth”. As an example, we validate a cloud property retrieval of the Institute of Atmospheric Physics of DLR and that of EUMETSAT’s Climate Monitoring Science Application Facility CMSAF. Cloud detection and cloud phase assignment perform well. By both retrievals 88% of the pixels are correctly classified as clear or cloudy. The DLR algorithm assigns the correct thermodynamic phase to 95% of the cloudy pixels and the CMSAF retrieval to 84%. Cloud top temperature is slightly overestimated by the DLR code (+3.1K mean difference with a standard deviation of 10.6 K) and to a very low extent by the CMSAF code (−0.12K with a standard deviation of 7.6 K).Both retrievals account reasonably well for the distribution of optical thickness for both water and ice clouds, with a tendency to underestimation. Cloud effective radii are most difficult to evaluate but the APICS algorithm shows that realistic histograms of occurrences can be derived (CMSAF was not evaluated in this context). Cloud water path, which is a combination of the last two quantities, is slightly underestimated by APICS, while CMSAF shows a larger scattering.
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 mW/m2 to 25.6 mW/m2. 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 with 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.
The libRadtran software package is a suite of tools
for radiative transfer calculations in the Earth’s atmosphere.
Its main tool is the uvspec program. It may be used to compute
radiances, irradiances and actinic fluxes in the solar and
terrestrial part of the spectrum. The design of uvspec allows
simple problems to be easily solved using defaults and included
data, hence making it suitable for educational purposes.
At the same time the flexibility in how and what input
may be specified makes it a powerful and versatile tool for
research tasks. The uvspec tool and additional tools included
with libRadtran are described and realistic examples of their
use are given. The libRadtran software package is available
from http://www.libradtran.org.
A method designed to track the life cycle of
contrail-cirrus using satellite data with high temporal and
spatial resolution, from its formation to the final dissolution
of the aviation-induced cirrus cloud is presented. The method
follows the evolution of contrails from their linear stage until
they are undistinguishable from natural cirrus clouds. Therefore,
the study of the effect of aircraft-induced clouds in the atmosphere is no longer restricted to linear contrails and can
include contrail-cirrus. The method takes advantage of the
high spatial resolution of polar orbiting satellites and the high
temporal resolution of geostationary satellites to identify the
pixels that belong to an aviation induced cloud. The high spatial
resolution data of the MODIS sensor is used for contrail detection, and the high temporal resolution of the SEVIRI
sensor in the Rapid Scan mode is used for contrail tracking.
An example is included in which the method is applied to the
study of a long lived contrail over the bay of Biscay.
This paper defines the meteorological state of the atmosphere which will give rise to the formation of condensation trails (contrails) as the exhaust from an aircraft engine mixes with and saturates the environment. Three basic assumptions were made with regard to the formation of visible contrails: (1) contrails are composed of ice crystals; (2) water vapor cannot be transformed into ice without first passing through the liquid phase, thus necessitating an intermediate state of saturation with respect to water; (3) a minimum visible water content of 0.004 gm/m3 is required for a faint trail and 0.01 gm/m3 for a distinct trail. This last requirement proved of no importance in determining whether or not a trail would form, but did affect its persistence.
Curves were constructed showing the critical temperature for the formation of a visible trail as a function of the pressure and relative humidity of the environment and the amount of air entrained into the exhaust. It is shown that these curves are applicable to any aircraft which has the same water to heat ratio in its exhaust as the case discussed in this report. In general this ratio is fairly constant regardless of the type of airplane, control settings, or fuel. The major exception occurs with aircraft powered by reciprocating engines in which case a considerable portion of the heat produced may be dissipated outside of the trail. A separate, but similar, study would be necessary for each aircraft with a significantly different proportion of such heat loss.
On the occasion of the 50th anniversary of the Institute of Atmospheric Physics of the German Aerospace Center (DLR), this book presents more than 50 chapters highlighting results of the institute’s research.
The book provides an up-to-date, in-depth survey across the entire field of atmospheric science, including atmospheric dynamics, radiation, cloud physics, chemistry, climate, numerical simulation, remote sensing, instruments and measurements, as well as atmospheric acoustics.
The authors have provided a readily comprehensible and self-contained presentation of the complex field of atmospheric science. The topics are of direct relevance for aerospace science and technology. Future research challenges are identified.
The radiative forcing from aviation-induced cirrus is derived from observations and models.
The annual-mean diurnal cycle of airtraffic in the North Atlantic region (NAR) exhibits two peaks in early morning and afternoon with different peak times in the western and eastern parts of the NAR. The same "aviation fingerprint" is found in eight years (2004-2011) of Meteosat observations of cirrus cover and outgoing longwave radiation (OLR). The observations are related to airtraffic data with linear response models assuming the background atmosphere without aviation to be similar to that observed in the South Atlantic.
The change in OLR is interpreted as aviation-induced longwave radiative forcing (LW RF).
The data analysis suggests a LW RF of about 600—900 mW m-2 regionally.
A detailed contrail-cirrus model for given global meteorology and airtraffic in 2006 gives similar results. The global RF is estimated from the ratio of global and regional RF as derived from three models. The extrapolation implies about 100--160 mW m-2 global LW RF. The models show large differences in the shortwave/longwave RF-magnitude ratio.
One model computes a ratio of 0.6, implying an estimate of global net RF of about 50 (40-80) mW m-2. Other models suggest smaller ratios, with less cooling during day, which would imply considerably larger net effects. The sensitivity of the results to the accuracy of the observations, traffic data, models and the estimated background is discussed.
[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.
Methods for detecting linear contrail pixels in satellite infrared
images are described. An objective contrail detection algorithm has been
developed and extensively applied to data from various polar and
geostationary satellite sensors. The method uses the contrast in
brightness temperatures near 11 and 12 μm wavelengths and detects
linear contrails using image processing techniques. The paper discusses
the development of the algorithms, detection efficiency, false alarm
rate, some of the results, and their validation. The contrail detection
algorithm detects only a fraction of all contrail cirrus. Progress is
expected from combining spatiotemporal satellite data in correlation
with traffic and meteorological data.
Air traffic effects high cloudiness and therefore the Earth's radiation
budget by producing contrail cirrus. Contrail cirrus comprise of
line-shaped contrails and irregularly shaped ice clouds that originate
from them. The warming effect of contrail cirrus is disproportionally
large at night, since at daytime the cooling due to the short wave cloud
albedo effect acts toward compensating the long wave warming effect.
Therefore it has been suggested to restrict air traffic to daytime in
order to reduce its climate impact. The potential for reducing the
contrail cirrus radiative forcing by shifting air traffic to daytime
depends on the diurnal cycle of contrail cirrus coverage which is in
turn determined by the diurnal cycle of air traffic and the contrail
cirrus lifetimes. Simulations with a global atmospheric general
circulation model indicate that the annual mean contrail cirrus coverage
may be almost constant over the day even in areas where air traffic is
close to zero at night. A conceptual model describing the temporal
evolution of contrail cirrus coverage reveals that this is due to the
large variability in contrail cirrus lifetimes in combination with the
spreading of contrail cirrus. This large variability of lifetimes is
consistent with observational evidence but more observations are needed
to constrain the contrail lifetime distribution. An idealized mitigation
experiment, shifting nighttime flights to daytime, indicates that
contrail cirrus radiative forcing is not significantly changed.
This work is two pronged, discussing 1) the morphology of contrails and their transition to cirrus uncinus, and 2) their microphysical and radiative properties. It is based upon the fortuitous occurrence of an unusual set of essentially parallel contrails and the unanticipated availability of nearly simultaneous observations by photography, satellite, automated ground-based lidar, and a newly available database of aircraft flight tracks. The contrails, oriented from the northeast to southwest, are carried to the southeast with a component of the wind so that they are spread from the northwest to southeast. Convective turrets form along each contrail to form the cirrus uncinus with fallstreaks of ice crystals that are oriented essentially normal to the contrail length. Each contrail is observed sequentially by the lidar and tracked backward to the time and position of the originating aircraft track with the appropriate component of the wind. The correlation coefficient between predicted and actual time of arrival at the lidar is 0.99, so that one may identify both visually and satellite-observed contrails exactly. Contrails generated earlier in the westernmost flight corridor occasionally arrive simultaneously with those formed later closer to the lidar to produce broader cirrus fallstreaks and overlapping contrails on the satellite image. The minimum age of a contrail is >2 h and corresponds to the longest time of travel to the lidar. The lag between the initial formation of the contrail and its first detectability by Moderate-Resolution Imaging Spectroradiometer (MODIS) is ≈33 min, thus accounting for the distance between the aircraft track and the first detectable contrail by satellite. The lidar also provides particle fall speeds and estimated sizes, optical extinction coefficients, optical thickness (tau = 0.35), and ice water path (IWP = 8.1 g m-2). These values correspond to the lower range of those found for midlatitude cirrus by Heymsfield et al. The ice water per meter of length along the cloud lines is 103 104 times that released by typical jet aircraft. The synthesis of these findings with those of prior investigators provides confidence in the present results. Various authors find that contrail-generated cirrus such as reported here contribute to net regional warming.
ERA-40 is a re-analysis of meteorological observations from September 1957 to August 2002 produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) in collaboration with many institutions. The observing system changed considerably over this re-analysis period, with assimilable data provided by a succession of satellite-borne instruments from the 1970s onwards, supplemented by increasing numbers of observations from aircraft, ocean-buoys and other surface platforms, but with a declining number of radiosonde ascents since the late 1980s. The observations used in ERA-40 were accumulated from many sources. The first part of this paper describes the data acquisition and the principal changes in data type and coverage over the period. It also describes the data assimilation system used for ERA-40. This benefited from many of the changes introduced into operational forecasting since the mid-1990s, when the systems used for the 15-year ECMWF re-analysis (ERA-15) and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis were implemented. Several of the improvements are discussed. General aspects of the production of the analyses are also summarized.
Though presently small in magnitude, aviation's future impact on climate will likely increase with the absence of effective mitigation measures. With the exception of CO(2) emissions, climate impacts of aviation emissions are quite uncertain, and there are scientific gaps that need to be addressed to guide decision making. An objective of the Next Generation Air Transportation System is to limit or reduce aviation's impact on climate. Therefore, the Federal Aviation Administration has developed the Aviation Climate Change Research Initiative (AC-CRI) to address key scientific gaps and reduce uncertainties while providing timely scientific input to advance and implement mitigation measures. This paper provides a brief overview of the priority-driven research areas that ACCRI has identified and that need to be pursued to better characterize aviation's impact on climate change.
Data from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on board the first Meteosat Second Generation (MSG) satellite have been available since February 2003. Four MSG satellites are planned to ensure an operational service until at least 2018. A software package, which derives from MSG/SEVIRI imagery a set of 12 products useful for nowcasting purposes, has been developed cooperatively by the Satellite Application Facility for supporting NoWCasting and very short range forecasting (SAFNWC) and is distributed by EUMETSAT.This paper describes the cloud mask (CMa) and type (CT) algorithms implemented in this SAFNWC/MSG software package. A multispectral thresholding technique has been used: the test sequence depends on illumination conditions and geographical location whereas most thresholds are dynamically computed from ancillary data (atlas, climatology maps, numerical weather prediction (NWP) model forecast fields) using radiative transfer models. These algorithms have been prototyped using GOES‐8 and MODIS imagery before being applied to MSG‐1/SEVIRI. The cloud mask and type can be extracted in any area inside the MSG full disk. Preliminary validation results obtained from a comparison with surface observations using a few months of MSG‐1/SEVIRI data show good performances.
By means of a scanning backscatter and depolarization lidar. contrails have been investigated for ages between a few seconds and 60 min. At environmental temperatures less than or equal to -60 degrees C the depolarization measured in the contrails rises from about 0.1 to 0.5 with time, whereas at higher temperatures around -50 degrees C already the youngest contrails exhibit depolarization values of about 0.5. This indicates a strong dependence of the aerosol formation and growth on the environmental temperature which might influence their behavior in the atmosphere.
After reviewing the indirect evidence for the regional climatic impact of contrail-generated cirrus clouds (contrail-cirrus), the author presents a variety of new measurements indicating the nature and scope of the problem. The assessment concentrates on polarization lidar and radiometric observations of persisting contrails from Salt Lake City, Utah, where an extended Project First ISCCP (International Satellite Cloud Climatology Program) Regional Experiment (FIRE) cirrus cloud dataset from the Facility for Atmospheric Remote Sensing has captured new information in a geographical area previously identified as being affected by relatively heavy air traffic. The following contrail properties are considered: hourly and monthly frequency of occurrence; height, temperature, and relative humidity statistics; visible and infrared radiative impacts; and microphysical content evaluated from in situ data and contrail optical phenomenon such as halos and coronas. Also presented are high-resolution lidar images of contrails from the recent SUCCESS experiment, and the results of an initial attempt to numerically simulate the radiative effects of an observed contrail. The evidence indicates that the direct radiative effects of contrails display the potential for regional climate change at many midlatitude locations, even though the sign of the climatic impact may be uncertain. However, new information suggests that the unusually small particles typical of many persisting contrails may favor the albedo cooling over the greenhouse warming effect, depending on such factors as the geographic distribution and patterns in day versus night aircraft usage.
In the spring of 1994, the first of the National Oceanic and Atmospheric
Administration's (NOAA's) next generation of geostationary satellites,
GOES-I, is scheduled for launch. The introduction of this major
component of NOAA's modernization represents a significant advance in
geostationary remote sensing. All major components of the GOES-1 system
are new or greatly improved: 1) the satellite is earth oriented to
improve instrument performance; 2) sounding and imaging operations are
now performed by different and separate instruments; 3) a five-band
multispectral radiometer with higher spatial resolution improves imaging
capabilities; 4) a sounder with higher radiometric sensitivity enables
operational temperature and moisture profile retrieval from
geostationary altitude for the first time; 5) a different data format is
used to retransmit raw data to direct receive users; and 6) a new ground
data processing system handles the high data volume and distributes
advanced products to a variety of users.This article describes the
features of the GOES-I spacecraft and instruments, imaging and sounding
schedules, data handling systems, and remote sensing products.
Simulations of GOES-1 imager and sounder products are presented and
compared with GOES-7 products. The simulations show that GOES-1 derived
product images, and sounder products should be significant improvements
in both frequency of coverage and accuracy.
Aviation induced cirrus (AIC) cover is identified from mean diurnal cycles of cirrus cover and air traffic density in the North Atlantic flight corridor. Traffic data for this region show an aviation “fingerprint” with two maxima during morning eastbound and afternoon westbound traffic. The same aviation fingerprint is found in cirrus cover. Cycle differences between west and east domain parts allow separating between aviation and natural diurnal changes. Cirrus cover is derived from 8 years of Meteosat infrared data. Linear contrail cover is estimated from the same data. Background cirrus without aviation impact is estimated from cirrus observations over the South Atlantic and from numerical weather prediction forecast. The cirrus cover cycle is well approximated by linear response to traffic density with fitted delay times of 2.3–4.1 h, implying AIC cover of 1–2%, more than expected from recent models.
A parametrization for ice supersaturation is introduced into the ECMWF Integrated Forecast System (IFS), compatible with the cloud scheme that allows partial cloud coverage. It is based on the simple, but often justifiable, diagnostic assumption that the ice nucleation and subsequent depositional growth time-scales are short compared to the model time step, thus supersaturation is only permitted in the clear-sky portion of the grid cell.
Results from model integrations using the new scheme are presented, which is demonstrated to increase upper-tropospheric humidity, decrease high-level cloud cover and, to a much lesser extent, cloud ice amounts, all as expected from simple arguments. Evaluation of the relative distribution of supersaturated humidity amounts shows good agreement with the observed climatology derived from in situ aircraft observations. With the new scheme, the global distribution of frequency of occurrence of supersaturated regions compares well with remotely sensed microwave limb sounder (MLS) data, with the most marked errors of underprediction occurring in regions where the model is known to underpredict deep convection. Finally, it is also demonstrated that the new scheme leads to improved predictions of permanent contrail cloud over southern England, which indirectly implies upper-tropospheric humidity fields are better represented for this region. Copyright
Crystal size and optical depth of optically thin cirrus clouds and contrails over the North Sea and Adriatic Sea on the 18th of October 1989 are retrieved by comparison of NOAA AVHRR/2 brightness temperatures of channel 4 (9.97 m–11.56 m) and channel 5 (11.075 m–12.76 m) with one dimensional radiative transfer calculations. Measured brightness temperatures in all three infrared channels and their differences show higher values for contrails than for cirrus. The radiative properties of young contrails are consistent only, if smaller crystal size than those given for natural cirrus are adopted for the calculations. However, there is a continuous transition in radiative parameters between clouds classified as natural cirrus or contrails. For the test areas ice clouds are classified with respect to optical depth and mean crystal size. Finally infrared fluxes and heating rates in the spectral range 4 m–40 m are calculated for an atmosphere with a 500 m thick contrail or cirrus uncinus. At given ice content a far stronger atmospheric warming is found for a contrail with relatively small ice crystals: up to 80 K/day at cloud base for an ice content of 0.05 gm–3 compared to 10 K/day for a cirrus uncinus with large crystals.
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.
Aviation makes a significant contribution to anthropogenic climate forcing. The impacts arise from emissions of greenhouse gases, aerosols and nitrogen oxides, and from changes in cloudiness in the upper troposphere. An important but poorly understood component of this forcing is caused by ‘contrail cirrus’—a type of cloud that consist of young line-shaped contrails and the older irregularly shaped contrails that arise from them. Here we use a global climate model that captures the whole life cycle of these man-made clouds to simulate their global coverage, as well as the changes in natural cloudiness that they induce. We show that the radiative forcing associated with contrail cirrus as a whole is about nine times larger than that from line-shaped contrails alone. We also find that contrail cirrus cause a significant decrease in natural cloudiness, which partly offsets their warming effect. Nevertheless, net radiative forcing due to contrail cirrus remains the largest single radiative-forcing component associated with aviation. Our findings regarding global radiative forcing by contrail cirrus will allow their effects to be included in studies assessing the impacts of aviation on climate and appropriate mitigation options.
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.
Aviation emissions contribute to the radiative forcing (RF) of climate. Of importance are emissions of carbon dioxide (CO2), nitrogen oxides (NOx), aerosols and their precursors (soot and sulphate), and increased cloudiness in the form of persistent linear contrails and induced-cirrus cloudiness. The recent
Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) quantified aviation’s RF contribution for 2005 based upon 2000 operations data. Aviation has grown strongly over the past years, despite world-changing events in the early 2000s; the average annual passenger traffic growth
rate was 5.3% yr-1 between 2000 and 2007, resulting in an increase of passenger traffic of 38%. Presented
here are updated values of aviation RF for 2005 based upon new operations data that show an increase in traffic of 22.5%, fuel use of 8.4% and total aviation RF of 14% (excluding induced-cirrus enhancement) over the period 2000–2005. The lack of physical process models and adequate observational data for aviationinduced cirrus effects limit confidence in quantifying their RF contribution. Total aviation RF (excluding induced cirrus) in 2005 was ~55mW m-2 (23–87mW m-2, 90% likelihood range), whichwas 3.5% (range 1.3–10%, 90% likelihood range) of total anthropogenic forcing. Including estimates for aviation-induced cirrus RF increases the total aviation RF in 2005–78 mW m-2 (38–139 mW m-2, 90% likelihood range),
which represents 4.9% of total anthropogenic forcing (2–14%, 90% likelihood range). Future scenarios of
aviation emissions for 2050 that are consistent with IPCC SRES A1 and B2 scenario assumptions have been
presented that show an increase of fuel usage by factors of 2.7–3.9 over 2000. Simplified calculations of total aviation RF in 2050 indicate increases by factors of 3.0–4.0 over the 2000 value, representing 4–4.7% of total RF (excluding induced cirrus). An examination of a range of future technological options shows that substantive reductions in aviation fuel usage are possible only with the introduction of radical technologies. Incorporation of aviation into an emissions trading system offers the potential for overall (i.e., beyond the aviation sector) CO2 emissions reductions. Proposals exist for introduction of such a system at a European level, but no agreement has been reached at a global level.