Wind farms and fuel additives possible
catalysts in the generation of spreading aviation contrails
by Dr Chris Barnes, Bangor Scientific and Educational Consultants, July
Since approximately 1997, sky watchers have noticed dramatic
changes in the behaviour of aviation contrails, particularly those under busy
air-lanes. The period has seen
contrails which spread out much more into elaborate shapes and patterns which
can under some conditions persist in the sky and even transform into cirrus
cloud. Rarely do contrails remain as the
fine pencil line of old. The present
author has also noticed contrails which spread out and produce fall-streaks
over part of the sky and then leave gaps with no contrail at all and then leave
line contrails towards the horizon.
These days the sun often looks more ‘halogenic’
as well. This together with the
observation of more cases of crepuscular rays and other rare optical
phenomena is an indicator of more
aerosols in the atmospheric environment and a greater range in size and shape
distribution in water droplets and ice crystals. Of course there will be others who never look
up and have noticed no significant difference in our skies.
The author has previously advanced hypotheses as to the cause
of spreading and persistent contrails and has discussed their weather and
climate implications (http://www.drchrisbarnes.co.uk/AIRWARM.htm). For example;
contrails may form easier and persist longer due to new types of
aircraft engine, the so called high bypass ratio, see Schumann (2000) and more
advanced aviation fuel with flame retardant and cleanser/lubricant properties,
see below. Also high sulphur fuels cause
longer contrails with more tendency to persist, see Schumann et al (1996) and
there is a threshold below which changing fuel sulphur concentration makes no discernible
visible effect, Busen and Schumann (1995). Aircraft density in the major flight corridors
is much higher so there is much more ice nucleation material, sulphate and
black carbon present. Aircraft can also
fly closer together due to wave avoidance technologies. Contrails are always likely to form in
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=206049&fileId=S0022112003007808. All these factors affect the type and number
density of contrails formed. Also
because of AMDAR (weather data collection technology employed on aircraft) they are required to make small, discrete,
jumps in cruise altitude. This too may change the form and shape of contrails. AMDAR has included information on atmospheric
super-saturation since 2006 (see Gierens et al 2008) so
may has the potential to be used in contrail avoidance strategy. However, the purpose of this paper is to
consider if wind farms are the main
catalyst or at least an additional
catalyst in the generation of such new
families of contrails. Jet fuels also contain mixtures of antioxidants,
detergent/dispersants, and metal deactivators, see Zarbarnick
and Grinstead (1994). In more detail; Additives
may be included in aviation fuels to improve fuel performance - generally by
eliminating undesirable effects - or to meet specific requirements of certain
aircraft or airline operators. They are added in quantities that are often only
measurable in parts per million.
The additive content of jet fuels varies considerably,
depending on whether the fuel is for civil or military use. Additive packages
for Avgas, on the other hand, are fairly standard. Only additives that have
been through a detailed and comprehensive evaluation and approval process are
Tetra-ethyl lead is added to improve the anti-knock
characteristics of Avgas. There are pressures to eliminate this additive on
environmental grounds. Alternative ways of boosting the octane rating of Avgas
have still to be found however.
Antioxidants (gum inhibitors) must be used in Avgas to
prevent the formation of gum and other antioxidation
products. Jet fuels, which are inherently more stable than gasolines,
may contain them, depending on the treatment process used during manufacture.
A metal deactivator - now rarely used - may be added to
nullify the effects of dissolved trace metals, especially copper, which can
impair the thermal stability of jet fuels.
Corrosion inhibitors can be used to reduce corrosion in fuel
system and improve the lubricity - lubricating
properties - of jet fuels.
Fuel system icing inhibitors reduce the freezing point of any
water that may be in the fuel system and prevent the formation of ice crystals
that could restrict fuel flow. They are mandatory in military Jet but are not
used in civil aircraft that have fuel heaters. They may be added to either Jet
or Avgas during the fuelling of small aircraft.
Static dissipater additives minimise the hazardous effects of
static charges that build up during movement of jet fuels. They are sometimes
used in Avgas as well, see Shell Global Website. Since the
precise balance and composition of these may vary from one type of fuel to
another, this too could potentially impact form and ice crystal size of contrails
especially if aerosol is released but
there appears to be nothing documented in the scientific literature. Although many aviation fuel manufacturers prefer to
list their fuel additives as 'trade secret', this is extremely unhelpful to
climate and atmospheric scientists. An extensive
'data mining' type search of the
scientific and patent literature suggest that ammonium, calcium aluminium and barium salts of dinonylnaphthalenesulfonic
acid would be the types of compounds used for corrosion inhibition and static dispersion.
acid has a micelle like structure and can be used for extracting metals from
aqueous organic mixtures, see amongst
others http://www.sciencedirect.com/science/article/pii/0022190279803656. Such
are 'Thermooxidatively' stable compositions, see http://www.google.com/patents/US5169564. In preventing static build up and corrosion
in aircraft engines, metal complex organic micelles will be released to the
atmosphere. It has recently been proposed that natural aerosols are organic aerosols in an ‘inverted micelle’ form consisting of an
aqueous core that is encapsulated in an inert, hydrophobic organic monolayer.
The organic materials that coat the aerosol particles are surfactants of
biological origin, see Barney Ellison et al (2012). Kulmala et al
(2004) have postulated that biogenic aerosol cools the planet in an negative
feedback response to increasing CO2, http://www.atmos-chem-phys.net/4/557/2004/acp-4-557-2004.pdf. Possibly the aerosol being inadvertently
released by the modern aircraft fleet may
act in a way similar to that of natural organic aerosol. If this is the case
ways could be conceived to enhance the process if SRM or large scale
geo-engineering were ever to be required.
Contrails and Wind
Lewellen and Lewellen
(2001) have shown the fraction of the initial contrail ice crystals surviving,
their spatial distribution, and the ice mass distribution are all sensitive to
the aircraft type, ambient humidity, assumed initial ice crystal number, and
ambient turbulence conditions and that there is a significant range of
conditions for which a smaller transport such as a B737 produces as significant
a persistent contrail as a larger transport such as a B747, even though the
latter consumes almost five times as much fuel.
Contrail horizontal extent is known to increase due to the wind shear,
see Jensen et al. Duda
et al (2004) showed that persistent contrail formation density was roughly
correlated with air traffic density. Liou and Ou reached a similar conclusion for the abundance of ‘high
Can wind farms
Wind farms are both sinks of energy and sources of
turbulence, see Roy 2004.
Large-scale use of wind power can alter local and global
climate by extracting kinetic energy and altering turbulent transport in the
atmospheric boundary layer, see Kieth et al, who also
showed that added turbulence intensity occurred downstream of a wind farm is
found for 7 of the 19 cases. Van
den berg (2007) states that atmospheric stability cannot, with respect to modern, tall wind turbines,
be viewed as a ‘small perturbation to a basic neutral state’. Barnes ( ref) has already suggested that
wind farms may be causing freak rainfall events in the uk. Wang and Prinn (2010) suggest that wind farms will cause alterations of the global
distributions of rainfall and clouds.
Since contrails are specialised clouds it is logical to suggest that
these too will be affected. Barrie and
Kirk –Davidoff (2010) calculate
significantly impact on the
atmospheric circulation due to the additional surface roughness forcing. This
forcing could be changed deliberately by adjusting the attitude of the
turbines. Induced perturbations involve substantial changes in the track and
development of cyclones over the North Atlantic, and the magnitude of the
perturbations rise above the level of forecast uncertainty. Clearly if storm tracks and circulation are
potentially so dramatically affected then so would be provision of CCN for contrails and
contrail cirrus. Wind farms also affect
the hydrometeorology of an area up to 18–23 km downwind, see Roy 2010. Large-scale deployment of wind power
may alter climate through alteration of surface roughness. Previous research
using GCMs has shown large-scale impacts of surface roughness perturbations but
failed to elucidate the dynamic mechanisms that drove the observed responses in
surface temperature. Using the NCAR Community Atmosphere Model in both its
standard and aqua planet forms, the authors have explored the impact of
isolated surface roughness anomalies on the model climate. A consistent Rossby wave response in the mean winds to roughness
anomalies across a range of model implementations is found. This response
generates appreciable wind, temperature, and cloudiness anomalies. The
interrelationship of these responses is discussed, and it is shown that the
magnitude of the responses scales with the horizontal length scale of the
roughened region, as well as with the magnitude of the roughness anomaly. These
results are further elucidated through comparison with results of a series of
shallow-water model experiments, see Kirk Davidoff and Kieth.
Seismic noise, infra-sound and AGW
Wind farms are also large
emitters of seismic noise, see Auld et al (2014). They will effect waves of the
ocean if offshore and emit infrasound.
A natural source of infrasound is microbaroms
or sea wave signals at approximately 0.2 Hz and 120dB. Microbarom wind
wave interaction can be two way and involve all levels of the troposphere, stratosphere and
thermosphere, see amongst other Garces 2004. Microbaroms provide a natural atmopsheric
probe, see Donn and Rind (1971). AGW is one coupling
mechanism for processes in the various parts of the atmosphere. Caveleri et al
(2012)has extensively addressed the problem in 'Wind Waves in the Coupled Climate System'. Gregory (2009) has discussed the rare phenomenon of
helical contrails over the sea. The present author has often observed such
'DNA like' trails in Bangor Wales which is a coastal city but feels that wind
farm turbulence could also explain them.
Wind farms emit infra-sound comb
spectra as harmonics of the blade
crossing frequency. This infra-sound has been detected 60km from wind farms,
see Pepyne Klaiber
(2012)(ams.confex.com). Although,perhaps, some 30 dB down on microbaroms . Liska has also observed long range 2Hz infrasound from
hydro-power stations (1974). Kulichkov (2004) discussed long range mesopheric
sound propagation in detail. Tidal
components have been observed by radar at Stratospheric and Mesopheric
heights, see Woodman and Guillen ( 1974).
There is thus no reason to suppose that Wind Farm infra=sound components
would not be present at or below these heights, say the UTLS for example where
many contrails are found.
Arrowsmith et al
(2010) describes the Siesmo-Acoustic wave-field as a
new paradigm in the study of geophysical phenomena and several natural and
anthropogenic sources are mentioned but
wind farms are perhaps erroneously omitted?
Contrails spread in upper atmosphere wind shear which is also the mechanism for infra-sound refraction, see Georges and Beasley (1977). It stands to reason therefore that wind turbine infra-sound will alter the shape and form of contrails.
Is this new family of
contrails 'planet friendly'
There is evidence to suggest that many
forms of contrails cool the planet by
day and warm it by night. There is
further evidence to suggest that NOx injection by aircraft
may also produce a somewhat unexpected cooling effect. Presumably if the contrails are spread out
more as a result of propagating disturbances from wind farms this may add to
the predicted cooling effects. However all other aircraft emissions are
highly undesirable either because of their climate warming effects or because
of their potential to be environmentally toxic.
Testing the wind farm hypothesis
Clearly not all the world's wind farms
and flight corridors correspond but it would be instructive to look at those
which do and then to contrast contrail coverage in heavily used flight
corridors where there are no wind farms. A crude visual geographic meta-analysis
can readily be done by using public domain mapping
take from the internet.
The world distribution of major wind farms is shown on the left. Contrail coverage is shown on the right together with the combined effect of increasing aircraft efficiency i.e. higher by-pass ratios. Clearly the east /west US/Europe routes are the most heavily used. The hypothesis would appear to be supported in that in every individual country the contrail coverage increases significantly over land where wind farms are in operation. Of course, to some extent, an abundance of internal flights in these regions in addition to international flights cannot be ruled out as being equally causative and further research will be required.
Some evidence has been provided that
wind farms may modify aircraft contrails but further work remains. Similarly aviation fuel additives may be
crucial in altering the types and balance of atmospheric aerosol. In the interests of scientific understanding
and possibly for all occupants of this planet it would be useful if fuel manufacturers
would disclose the chemical composition of all of their additives.
If flying is restricted to the daytime it may
be more climatically friendly. In a changing global environment no stone should be left unturned to make sure
that there are no unpleasant or irreversible climactic surprises lurking
in the near future.