Interesting articles about contrail research

[skephu]

Thanks to the chemtrail theory, I got interested in the science of contrails, and I sometimes browse the latest articles on Google Scholar. So I thought a thread in which we report on the latest findings or interesting new articles could be useful.

I just found this one:

Bernhardt, J. and Carleton, A. M. (2015):
The impacts of long-lived jet contrail ‘outbreaks’ on surface station diurnal temperature range.
Int. J. Climatol.. doi: 10.1002/joc.4303

Multiple persistent jet aviation contrails – contrail ‘outbreaks’ – occur frequently over certain portions of the Continental United States (CONUS). The artificial cloudiness generated by contrail outbreaks alters the atmospheric radiation budget, potentially impacting the surface air temperature, particularly the diurnal temperature range (DTR), or difference between daytime maximum and nighttime minimum temperatures. This study evaluates the hypothesis that contrail outbreaks reduce the DTR relative to clear-sky conditions. We utilize a database of longer-lived (>4 h duration) jet contrail outbreaks for the CONUS previously determined from interpretation of high-resolution satellite imagery, for the January and April months of 2008 and 2009. The outbreak impact on DTR was determined by comparing maximum and minimum temperatures at pairs of surface weather stations (one outbreak and one non-outbreak) across two regions of climatologically high outbreak frequency; the South in January, and Midwest in April. We ensured that each station pair selected had broadly similar land use-land cover, soil moisture, and synoptic air mass conditions. For outbreaks in the South (January), there was a statistically significant reduction of DTR at the outbreak versus non-outbreak stations. This result was similar to that obtained for a smaller subset of outbreaks for which lower-level clouds could be confirmed as being absent (from North American Regional Reanalysis (NARR) output). For the Midwest (April), the results are mixed; statistically different for satellite-retrieved outbreaks, but not significantly different for the NARR-validated dataset. These results suggest that persistent jet contrails should be considered in short-term weather forecasting, and for their potential influence on the climatology of more frequently impacted areas.

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[skephu]

Recently, a new method for contrail cirrus prediction has been developed. It's called CoCiP, and it is described in this paper:

Schumann, U:
A contrail cirrus prediction model
Geosci. Model Dev., 5, 543-580, 2012

Abstract:

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.

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Some of the interesting figures:

Contrail forming flight paths (cyan) for global traffic between 03:00–06:00 UTC 6 June 2006. Contrails existing at 06:00 UTC that day are identified by red lines. Those parts of the tracks where these contrails originated are shown in black

Optical depth of contrail cover:

 

[skephu]

A more recent conference paper also shows the limitations of the CoCiP contrail prediction method:

Schumann U et al.:
Contrail Cirrus Forecasts for the ML-CIRRUS Experiment and Some Comparison Results

Abstract:

Model simulations with the contrail cirrus prediction model CoCiP driven by numerical weather prediction (NWP) data provided from the European Centre for Medium Range Forecasts (ECMWF) and global aircraft waypoint data show a mean computed cover (for optical depth larger than 0.1) of 0.23% globally, and 5.4% over mid Europe (Schumann and Graf, JGR, 2013). The computed mean longwave radiative forcing (RF) reaches 3 W m-2 over mid Europe (10°W-20°E and 40°N-55°N), and 0.13 W m-2 globally. The global net RF is about 40-60% smaller because of compensating shortwave cooling induced by contrails during daytime. The results depend on several model details such as the number of ice particles forming from aircraft soot emissions, the contrail plume dispersion, ice particle sedimentation etc., all influencing contrail life time and their optical properties. The quantitative results depend also strongly on ambient relative humidity, vertical motion and on ice water content of other cirrus predicted by the NWP model. In order to test and possibly improve this and other contrail models, high-quality observations are needed to which multi-parameter model output can be compared. The Mid-Latitude Cirrus Experiment ML-CIRRUS was performed (see C. Voigt et al., this conference) with a suite of in-situ and Lidar instruments for airborne measurements on the research aircraft HALO. Before and during the mission, CoCiP was run daily to provide 3-days forecasts of contrail cover using operational ECMWF forecasts and historical traffic data. CoCiP forecast output was made available in an internet tool twice a day for experiment planning. The one-day and two-day contrail forecasts often showed only small differences. Still, most recent forecasts and detailed satellite observations results were transmitted via satellite link to the crew for onboard campaign optimization. After the campaign, a data base of realistic air traffic data has been setup from various sources, and CoCiP was rerun with improved ECMWF-NWP data (at one-hour time resolution). The model results are included in the HALO mission data bank, and the results are available for comparison to in-situ data. The data are useful for identifying aircraft and other sources for measured air properties. The joint analysis of observations and model result has basically just started. Preliminary results from comparisons with lidar-measured extinction profiles, in-situ measured humidity, nitrogen oxides, and aerosol and ice particle concentrations, and with meteorological observations (wind, temperature etc.) illustrate the expected gain in insight. The contrail forecasts have been checked by comparison to available data including satellite data and HALO observations. During the campaign, it became obvious that predicted contrail cirrus cover compared qualitatively mostly well with what was found when HALO reached predicted cirrus regions. From the analysis of the measured data, some examples of significant correlation between model results and observations have been found. However, the quantitative agreement is not uniform. As expected, nature is far more variable than a model can predict. The observed optical properties of cirrus and contrails vary far more in time and space than predicted. Local values were often far higher or lower than mean values. A one-to-one correlation between local observations and model results is not to be expected. This inhomogeneity may have consequences for the climate impact of aviation induced cloud changes.

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[Jay Reynolds]

Ulrich Schumann I had some email conversations with him nearly 15 years ago when I was doing background work trying to understand contrail physics. He has that much experience with the "chemtrails" hoax. Not quite as cool as Hermann Mannstein, though.

 

[Henk001]

Still under review, but with a refreshing new take on the relation between contrails and climate change: instead of looking at the effect of contrails on climate, they model the effect of climate change on the occurrence of contrails untill the end of the 21st century:http://www.earth-syst-dynam-discuss.net/6/317/2015/esdd-6-317-2015.html

Ice-supersaturation (ISS) in the upper-troposphere and lower stratosphere is important for the formation of cirrus cloud and long-lived contrails. We analyse projected changes to 250 hPa ISS distribution and frequency over the twenty-first century using data from the RCP8.5 simulations of a selection of CMIP5 models. The models show a global-mean annual-mean decrease in ISS frequency of 4% by the end of the twenty-first century, relative to the present-day period 1979–2005. Changes are analysed in further detail for three sub-regions where air traffic is already high and increasing (Northern Hemisphere mid-latitudes) or expected to increase (tropics and Northern Hemisphere polar regions). The largest change is seen in the tropics, where a reduction of around 9% in ISS frequency by the end of the century is driven by the strong warming of the upper troposphere. In the Northern Hemisphere mid-latitudes the multi-model mean change is an increase in ISS frequency of 1%; however the sign of the change is not only model-dependent but also has a strong latitudinal and seasonal dependence. In the Northern Hemisphere polar regions there is an increase in ISS frequency of 5% in the annual-mean. These results suggest that over the 21st century climate change may have large impacts on the potential for contrail formation; actual changes to contrail cover will also depend on changes to the volume of air traffic, aircraft technology and flight routing.

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[skephu]

This is an old paper from 1971 which presents some observations pointing to the possibility that contrails may influence precipitation patterns by ice crystals from contrails falling into lower clouds and seeding them. I don't really know what more recent research has revealed about this, but it is known that ice crystals from contrails can grow as big as 2 mm in diameter and fall out of the contrail into lower clouds.

Dingle, AN: Man-Made Climatic Changes: Seeding by Contrails
Science 173.3995 (1971): 461-462.

 

[skephu]

An interesting paper about how contrails change the hydrological cycle in the atmosphere:

Schumann, U., Penner, J. E., Chen, Y., Zhou, C., & Graf, K. (2015). Dehydration effects from contrails in a coupled contrail–climate model. Atmospheric Chemistry and Physics, 15(19), 11179-11199.
PDF

Abstract. 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 lev-
els. 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 cir-
rus 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 lev-
els. Simulations with and without coupling are compared.
The drying at contrail levels causes thinner and longer-lived
contrails with about 15 % reduced contrail radiative forc-
ing (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 dehy-
dration 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 hydro-
logical cycle in the atmosphere by reducing the total water
column and the cover by high- and low-level clouds. For nor-
mal 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.

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It's interesting and counter-intuitive that the reduction in relative humidity causes longer-lived contrails. I think this is because in the drier air, ice particles grow slower, remain smaller, and therefore fall slower as well. But I guess this only applies if the RHi still remains above 100%.

The paper also states:

Falling ice particles may enhance pre-
cipitation from mixed-phase or warm clouds at lower alti-
tudes by increasing humidity and thus the liquid water con-
tent or by the Wegener–Findeisen–Bergeron process, both of
which are thought to increase the likelihood of precipitation
(Murcray, 1970; Korolev and Mazin, 2003; Yun and Penner,
2012).

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[Marin B]

This isn't recent, but it might be useful since it cites a lot of early papers and so provides somewhat of a review on the study of contrails.

James Q. DeGrand ,Andrew M. Carleton ,David J. Travis, and Peter J. Lamb: A Satellite-Based Climatic Description of Jet Aircraft Contrails and Associations with Atmospheric Conditions, 1977–79. Journal of Applied Meteorology, 39, 1434–1459 (2000)

Here's another from 2000, that is interesting because it has a world map showing contrail coverage in 1992 and predicted coverage for 2050:
Richard Miake-Lye, Ian Waltz, David Fahey, Howard Sesoky, and Chowen Wey: Aviation and the Changing Climate. Aerospace America, Sept. 2000, p 35-39.

 

[Henk001]

There are a number of articles that deal with mitigating the climate impact of contrail cirrus or cirrus clouds in general. Two interesting aspects I would like to put forward.
1. Contrary to the chemtrail belief, cirrus, and contrail cirrus in particular, have a warming effect, not cooling. So the idea of chemtrails as a way of cooling the warming earth is nonsense.
2. Cloud seeding of cirrus clouds is proposed in a number of articles to reduce the warming effect of (contrail) cirrus. Which means that, ironically, climate-engineering is proposed to reduce the effect of contrails (and cirrus in general).
A few examples:

Abstract. Cirrus clouds, thin ice clouds in the upper troposphere, have a net warming effect on Earth's climate. Consequently, a reduction in cirrus cloud amount or optical thickness would cool the climate. Recent research indicates that by seeding cirrus clouds with particles that promote ice nucleation, their lifetimes and coverage could be reduced. We have tested this hypothesis in a global climate model with a state-of-the-art representation of cirrus clouds and find that cirrus cloud seeding has the potential to cancel the entire warming caused by human activity from pre-industrial times to present day. However, the desired effect is only obtained for seeding particle concentrations that lie within an optimal range. With lower than optimal particle concentrations, a seeding exercise would have no effect. Moreover, a higher than optimal concentration results in an over-seeding that could have the deleterious effect of prolonging cirrus lifetime and contributing to global warming.

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Storelvmo et al: Cirrus cloud seeding has potential to cool climate
http://onlinelibrary.wiley.com/doi/10.1029/2012GL054201/full (GRL 2013)

Abstract. Greenhouse gases and cirrus clouds regulate outgoing longwave radiation (OLR) and cirrus cloud coverage is predicted to be sensitive to the ice fall speed which depends on ice crystal size. The higher the cirrus, the greater their impact is on OLR. Thus by changing ice crystal size in the coldest cirrus, OLR and climate might be modified. Fortunately the coldest cirrus have the highest ice supersaturation due to the dominance of homogeneous freezing nucleation. Seeding such cirrus with very efficient heterogeneous ice nuclei should produce larger ice crystals due to vapor competition effects, thus increasing OLR and surface cooling. Preliminary estimates of this global net cloud forcing are more negative than –2.8 W m–2 and could neutralize the radiative forcing due to a CO2 doubling (3.7 W m–2). A potential delivery mechanism for the seeding material is already in place: the airline industry. Since seeding aerosol residence times in the troposphere are relatively short, the climate might return to its normal state within months after stopping the geoengineering experiment. The main known drawback to this approach is that it would not stop ocean acidification. It does not have many of the drawbacks that stratospheric injection of sulfur species has.

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Mitchell&Finnegan: Modification of cirrus clouds to reduce global warming
http://iopscience.iop.org/article/10.1088/1748-9326/4/4/045102/fulltext/#erl314272s4(ERL 2009)

Abstract. Aircraft contrails and the cirrus clouds arising from them contribute substantially to aviation-induced climate forcing. The share of aviation in anthropogenic climate change can be reduced by avoiding contrail cirrus formation. The mitigation potential of altering the contrail formation stage is explored using a microphysical model to show how reductions in soot particle number emissions from jet engines, reductions in mean soot particle size, and a decrease in the supersaturation of aircraft exhaust plumes substantially lowers the optical depth of young contrails thereby decreasing the occurrence, lifetime, and radiative impact of contrail cirrus. The improved scientific understanding of initial ice formation processes allows atmospheric effects of mitigation options related to contrail cirrus to be investigated in unprecedented detail, especially those associated with the use of alternative aviation fuels. This study will enable a leap forward toward more reliable simulations addressing global climatic effects of contrail-induced cloudiness.

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Kärcher: The importance of contrail ice formation for mitigating the climate impact of aviation
http://onlinelibrary.wiley.com/doi/10.1002/2015JD024696/full (JGR 2016)