Contrails - Research, comments and links
Contrails and Aviation-cirrus
Clouds (01)
Clouds and the climate system
Clouds play a critical role in the Earth's hydrologic cycle and in the energy balance of the climate system. They have a strong effect on solar heating by reflecting part of the incident solar radiation back to space. An increase in the average albedo of the Earth-atmosphere system by only 10 percent could decrease the surface temperature to that of the last ice age. Clouds affect the thermal cooling by intercepting part of the infrared radiation emitted by the Earth and atmosphere below the cloud, and re-emitting part of this radiation back to the surface. Global change in surface temperature is highly sensitive to cloud amount and type. Increasing low-level and middle-level clouds has a net cooling effect because they reflect more solar radiation and have a relatively small effect on infrared radiation. On the other hand, increased high clouds will have a warming effect by virtue of their low temperature and reduced cooling to space. High cirrus also act as a natural cloud seeder and strongly modulate the radiatively-important upper tropospheric water vapor budget. Given the sensitivity of the global climate to clouds, it is not surprising that the largest uncertainty in model estimates of global warming is due to clouds.
Climate models and remote sensing depend on plane-parallel models. These employ ``effective" cloud parameters, such as cloud liquid water content, which depend on the macrophysical and microphysical properties of clouds. Inhomogeneous fractal cloud models are used to study the dependence of effective cloud parameters on macrostructural parameters such as the variance and wavenumber spectra of cloud liquid water. Determination of both macrophysical and microphysical cloud properties on horizontal scales from a few tens of meters to hundreds of kilometers, based on measurements taken from surface, aircraft and satellite platforms, allow plane-parallel and fractal cloud models to be tested and tuned for various meteorological conditions. Fractal cascades designed for various cloud types generate cloud layers having a range of inhomogeneities, and Monte Carlo methods then determine the radiative properties of such clouds. Fractal clouds are generally less reflective than plane-parallel clouds which have the same total cloud liquid water, and equivalently fractal clouds contain more liquid water than plane-parallel clouds which have the same reflectivity. When tuned to have realistic inhomogeneities, fractal clouds provide a connection between local measurements made in real clouds and idealized plane-parallel clouds employed by large-scale models.
Computations of cloud reflection, absorption and transmission for highly inhomogeneous clouds rely on various 3-dimensional radiative transfer techniques, such as Monte Carlo, spherical-harmonic discrete ordinates, or diffusion. An Intercomparison of 3D Radiation Codes (I3RC) is now underway to determine the efficiency and relative accuracy of the various methods.
Measurements of cloud radiative properties are conducted using airborne scanning radiometers and imaging spectrometers. For example, the Cloud Absorption Radiometer (CAR) is a multi-wavelength scanning radiometer that measures the angular distribution of scattered radiation. The retrieved cloud properties from these measurements are compared with simultaneous in situ measurements of cloud microphysics. The methods have been used to develop remote sensing capability from spaceborne platforms, to study cloud properties in regional areas, and to study the interaction of clouds with aerosol particles and their combined climatic impact. An extensive series of field observations since 1990 have been made with the MODIS Airborne Simulator. Recent activity involves measuring and studying the impact of ship effluents on cloud properties. Existing on a small scale, ship tracks provide a useful laboratory for the study of cloud microphysical changes as well as tests of instrumentation and remote sensing and retrieval algorithms. The extrapolation of ship track measurements to the global-scale climate is a difficult problem which is still being studied.
The effect of cirrus clouds on climate and chemistry
EPA
Identifier: U91-5367
Title:
The effect of cirrus clouds on climate and chemistry
Institution: University of Colorado at
Boulder
Proposed Start Date:
The effect of cirrus clouds on climate and chemistry has recently
become a focus of scientific interest. Cirrus clouds play a dual role in the
earth's radiation budget, increasing the earth's albedo while simultaneously
decreasing emission of infrared radiation to space. It is believed that these
combined effects cause a net warming at the earth's surface. Cirrus clouds may
also play a role in heterogeneous chemistry in the upper troposphere,
particularly in mid-latitude ozone depletion. Determining the conditions under
which cirrus clouds form is thus essential for accurate modeling of climate
and chemistry in the atmosphere. It is thought that cirrus clouds form
naturally in the upper troposphere, when highly dilute sulfate aerosols cool
and become supersaturated with respect to ice. These cloud particles freeze
homogeneously when water vapor reaches ice supersaturations of approximately
1.5. It has been suggested that cirrus clouds could also form from
heterogeneous nucleation on insoluble solids. A recent focus of study has been
on the formation of ice clouds on soot particles, a by-product of fossil fuel
combustion at the surface and from aircraft emissions throughout the
atmosphere. For such heterogeneous nucleation to be efficient, soot must serve
as a suitable nucleus for ice formation. If it does serve as an effective
nucleus, soot from anthropogenic sources may play an important role in the
formation of cirrus clouds, thereby affecting the clouds' impact on the
earth's radiation budget and the heterogeneous chemistry which occurs on these
clouds. Soot may also serve as a reactive surface for heterogeneous chemistry
throughout the troposphere. With an atmospheric lifetime of 4 - 12 months,
soot could play a major role in tropospheric chemistry.
- To begin to understand the effects of cloud type on radiative energy.
- To help understand how clouds affect the Earth's climate.
Soot particles are believed to be hydrophobic, and so they must be chemically processed for heterogeneous nucleation of ice to be efficient. However, the mechanism of soot activation in the atmosphere is still unresolved, and little laboratory work has been done to investigate this process. I am conducting nucleation studies of H2SO4/H2O, (NH4)HSO4/H2O and NH4)2SO4/H2O with compositions representative of the upper troposphere on soot aerosols. These studies are done under temperature and humidity conditions representative of the upper troposphere. In my experiments, a fluidized bed is used to generate a constant output of dry, solid soot particles. These particles pass through two virtual impactors so that a narrow size range of particles can be selected, and then they pass over a heated H2SO4/H2O solution. Supersaturated H2SO4 vapor may condense on the soot particles heterogeneously. Single particles are then sampled using scanning electron microscopy to determine if the soot has been coated with H2SO4 and/or H2O. After determining if the soot is coated, the soot/H2SO4/H2O aerosols are cooled in a flow tube to upper tropospheric temperatures, and their physical properties are observed. A dew-point hygrometer and a mass spectrometer are used to determine water vapor, allowing for determination of aerosol composition, and Fourier transform infrared spectroscopy is used to determine aerosol phase, allowing for the detection of ice crystallization. From these experiments, I expect to be able to qualitatively determine how efficiently H2SO4, H2O and NH3 condense on soot. This is important for understanding the environment and hence the reactivity and toxicity of soot in the troposphere. I will also quantitatively determine the efficiency of soot as a heterogeneous nucleus for ice in sulfate solution aerosols. From these data, an accurate determination of the extent to which heterogeneous nucleation occurs in cirrus cloud formation can be made, providing valuable insight into determining the effect of anthropogenic soot on atmospheric chemistry and climate.
Last Updated: October 9, 1998
Columns & Rubrieken Columns Karel Knip
Ongeforceerd kan het nu verder naar een ander klimaatprobleem waarvoor lezer Robert C. van W. in Amstelveen al vele jaren en in wisselende toonaard aandacht vraagt: de toenemende hoeveelheid vliegtuigsporen aan de hemel. Van W. ziet in de condensstrepen ('contrails'), die op nare dagen makkelijk uigroeien tot hemelbedekkende sluierbewolking, het bewijs dat het vliegverkeer het klimaat rechtstreeks be�nvloedt. Al een jaar of vijf maakt hij foto-opnamen als het weer heel erg is, en het AW-docucentre bezit inmiddels een fraaie collectie.
Can Airplanes Create Clouds and Cause the Climate to Change?
The ghostly white trails following airplanes and rockets through the sky, called contrails, are probably adding to global warming, according to scientists at NASA�s Langley Research Center, Hampton, Va. Atmospheric scientist Patrick Minnis uses GOES to track contrails that are formed when water vapor turns to ice in the exhaust of aircraft and rockets. The contrails often turn into cirrus clouds, a thin, wispy type of cloud made of ice crystals. While some clouds tend to help cool the globe and negate the affects of global warming, thin cirrus clouds are heat trappers, holding in more heat than they reflect back into space.
Because clouds come and go with the wind, GOES� clear, constant perspective is the only way to keep tabs on the changing contrails. The Imager, an instrument aboard GOES, can tell one cloud type from another by the cloud�s temperature, revealing to scientists which clouds are doing the heating, and which are doing the cooling. The work is part of a NASA�s Atmospheric Effects of Aviation Project to study the global and regional affects of contrails and the clouds they form. https://hyperion.gsfc.nasa.gov/AEAP
Another part of the aircraft-climate equation is pollution from airplanes and rockets. Anne Thompson, an atmospheric scientist at NASA�s Goddard Space Flight Center, Greenbelt, Md., uses GOES to guide her research into the top of the troposphere, the part of the atmosphere 5.5 to 7.5 miles (9-12 kilometers) above the Earth. The sky over the Atlantic Ocean has become a superhighway for air traffic, and in 1997, Thompson tested the air there from a NASA DC-8 to see the affect of airliner exhaust.
But pollution can also get to the troposphere during a thunderstorm, sending up man-made smog from below. GOES can identify where thunder clouds are, helping Thompson tell where thunderstorms are causing the pollution, and where smog is just the result of jet exhaust. Pollution in the troposphere is made up of gases that can trap heat from the sun and add to global warming, said Thompson. So knowing how airliners and rockets add to the picture is important for climate research. The study is also part of NASA�s Atmospheric Effects of Aviation Project.
Climate and Clouds: What�s the Connection?
If temperatures rise globally, what will the affect be on clouds, the Earth�s natural shade-makers? Since 1995, NASA Goddard climate researcher Gyula Molnar has used GOES to keep watch over low-lying stratus clouds blanketing the Eastern Pacific Ocean along the Peruvian, Chilean, and Baja California coasts. When the climate changed with El Ni�o in 1997 and the Eastern Pacific sea surface warmed up, the blanket of clouds became thinner and full of larger holes, allowing more of the sun�s heat to further warm the ocean.
Many climate scientists predict that sea surface temperatures around the globe will heat up with man-made global warming. If marine stratus clouds around the globe act like the clouds in the Eastern Pacific, the Earth�s land and sea surfaces could be in for a lot more heat during the predicted global warming. Molnar has used GOES to get an update every three hours since 1995 on the extent and brightness of clouds in the Eastern Pacific.
How Do Clouds Affect Radiative Energy?
One objective of the U.S. Department of Energy's Atmospheric Radiation
Measurement (ARM) Project is to determine the various radiative properties
of different cloud types. For example, because cumulus clouds form closer
to the ground than do cirrus clouds, they emit more radiation according to
the Stefan-Boltzmann law. The effect of cloud type on Earth's radiation
budget is one of the great unanswered questions of climatology. In this
exercise, students will begin to understand the complex interactions
between clouds, the atmosphere and the surface energy budget.
"But did the clouds form because the colder air had a lower holding capacity for water vapor than the warm air? If you believe a legion of teachers (from grade school to university), TV weather broadcasters, and endless textbook writers, this is the reason. They speak of the air being saturated and one even published an illustration of the air being wrung out like a sponge as the temperature dropped (sigh...). Unfortunately, it is not true. Sure, a cloud may form as the temperature drops, but not because some mystical holding capacity of the air has decreased."[..]
The air (mainly nitrogen and oxygen) no more has a holding capacity for water vapor, than, say, water vapor has for nitrogen. The atmosphere is a mixture of gases. While saturation (which involves bonds between different molecules) is a real phenomenon in liquids it does not describe the interaction of atmospheric constituents.[..]
"Water molecules are constantly coursing back and forth between phases (another word for the three states: vapor, liquid, and solid). If more molecules are leaving a liquid surface than arriving, there is a net evaporation; if more arrive than leave, a net condensation. It is these relative flows of molecules which determine whether a cloud forms or evaporates, not some imaginary holding capacity that nitrogen or oxygen have for water vapor.[..]
The rate at which vapor molecules arrive at a surface of liquid (cloud drop) or solid (ice crystal) depends upon the vapor pressure.[..]
But don't ever teach nonsense by claiming that the air has a temperature-dependent holding capacity for water vapor.[..]"
Before writing me with a question about this page, please check the Bad Clouds FAQ to see if the issue has already been addressed satisfactorily.
Source: Bad Clouds
https://www-loa.univ-lille1.fr/~boucher/preprints/contrail/node1.html
1. Introduction
Cloudiness is one of the meteorological parameters, with temperature and precipitation, which is the most perceptible to our common sense. It has been observed for a long time and is potentially indicative of climate change. Variations and trends in cloudiness have been reported by several authors over various regions and time periods (Angell and Korshover, 1975; Angell et al., 1984; Angell, 1990; Elliott and Angell, 1997, Henderson-Sellers, 1989, 1992; Karl and Steurer, 1990; Plantico et al., 1990; Seaver and Lee, 1987). Few studies examined specifically the trends in high-level clouds. Some authors have nevertheless attributed the increased cloudiness to jet aircraft operations which began in the 1960s (Machta and Carpenter, 1971; Changnon, 1981; Liou et al., 1990). [..]
There are two mechanisms suggested to increase high cloudiness from aviation: i) the formation of contrails and their subsequent transformation into cirrus (Schumann and Wendling, 1990; Minnis et al., 1998a) and ii) the later development of cirrus from exhaust aerosols (Jensen and Toon, 1997). As evidences in favour for the first mechanism, it has been observed that condensation trails (contrails) can advect great distances and appear to observers as natural cirrus (Minnis et al., 1998a). Contrails form when the mixture of the warm and humid exhaust gases and the cold and less humid ambient air exceeds water saturation (Schumann, 1996). To be of climatic importance, this mechanism requires that natural cirrus would not have appeared in place of these contrail-cirrus clouds. Ground-based observations of persistent and non-persistent contrails reported by Minnis et al. (1997) show that this may indeed be the case. The probability for contrail occurrence when cirrus are not observed is 7.3%, smaller than the probability for contrail occurrence when cirrus are present (24.8%), but still important enough to induce an additional cirrus coverage from aviation. The second mechanism is supported by the fact that if the soot particles injected by jet aircraft are good ice nuclei, they can allow ice nucleation at lower supersaturations than those required under natural conditions, resulting in an increase in the areal coverage of cirrus clouds (Jensen and Toon, 1997). This mechanism is difficult to quantify as it depends on environmental conditions (i.e., how often the upper troposphere is supersaturated with respect to ice without cirrus formation) and particle properties (i.e., their ice nuclei activation spectrum). While the first mechanism is localised in or close to the main flight corridors, the second mechanism can occur well away downstream from the source regions.Minnis et al. (1997) computed a significant (positive) correlation between mean contrail frequency over the United States and aviation fuel use (on 3[..]
Boucher Olivier
6/29/1998
www-loa.univ-lille1.fr/~boucher/
preprints/contrail/node1.html - 8k -
Cloud Radiative Processes
https://es.epa.gov/ncerqa_abstracts/fellow/98/prenni.html
Clouds play a critical role in the Earth's hydrologic cycle and in the energy balance of the climate system. They have a strong effect on solar heating by reflecting part of the incident solar radiation back to space. An increase in the average albedo of the Earth-atmosphere system by only 10 percent could decrease the surface temperature to that of the last ice age. Clouds affect the thermal cooling by intercepting part of the infrared radiation emitted by the Earth and atmosphere below the cloud, and re-emitting part of this radiation back to the surface. Global change in surface temperature is highly sensitive to cloud amount and type. Increasing low-level and middle-level clouds has a net cooling effect because they reflect more solar radiation and have a relatively small effect on infrared radiation. On the other hand, increased high clouds will have a warming effect by virtue of their low temperature and reduced cooling to space. High cirrus also act as a natural cloud seeder and strongly modulate the radiatively-important upper tropospheric water vapor budget. Given the sensitivity of the global climate to clouds, it is not surprising that the largest uncertainty in model estimates of global warming is due to clouds.
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