Persistent contrails laid down at night-time in North Wales gave a high probability of large local warming with 3 day  delays on the other hand those laid down in the daytime  often resulted in cooling after an  average 4.8 day delay  and in association with cooling particular physical  features of contrail cirrus   seemed to herald excessive precipitation, by Dr Chris Barnes, Bangor Scientific and Educational Consultants 

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Persistent contrails with a variety of distinct temperature and hydrological effects have been noted but overall the present trend in North Wales is towards cooling.   New nano-particles in the marine boundary layer could be the pre-cursor.   Warming persistent contrails, those laid down at circa 8 pm,  appeared to be capable of causing an average 8.2C rise in ground level  daytime air   temperature over a 3 day period.  Cooling persistent contrails, those laid down in daytime  were capable of causing an average of 7.1 C cooling in 4.8 days.  The difference is ascribed to photochemistry and initiation of  low level stratospheric ozone depletion in the day time case. Other differences can be in particle entrainment and ice crystal size and morphology.      The findings quite staggering suggest that at least in North Wales aviation controls the entire microclimate. A global extension of the model would seem feasible.     Weather and climate control using contrails as first proposed by Murcray in 1970 would now seem within human kind's grasp.   Two new climate negative feedback mechanisms are also explained and introduced in this work. 



There has been much debate concerning the climatic effect of persistent contrails.  The present author has very recently shown that in North Wales during 2005-2007 these contrails had a variety of distinct temperature and hydrological effects, including warming, cooling and cooling with excessive rainfall (1).    Yet overall there appeared to be a slight cooling effect, meaning at least in North Wales, cooling event must presently be outweighing warming events.


It has been suggested that flying at night should be avoided (2). This present work suggests that we should perhaps re-examine this notion in that too much daytime flying might tip the balance towards excessive     sive cooling especially of regions under busy air lanes and could also sicken populations by reducing u/v and vitamin D.

There  has been huge volumes of literature on contrails but very few on the direct effects of solar radiation on contrail formation and persistence.      Very recently indeed this has stated to change. For instance Myhre and  Stordal (2001) (3) have shown  that the solar forcing is negative and the magnitude maximizes for high solar zenith angles and that altering the time for aircraft traffic has the potential for reducing the radiative forcing due to contrails, and under certain assumptions could give a net zero forcing.


The separate warming and cooling effects effect observed by  Barnes (1) might be elegantly be accounted for by the observation of Birmili and  Wiedensohler (2000) (4) who have found new nano-particle formation in the polluted continental boundary layer based on 1.5-year observations of the particle size distribution, meteorological and gas phase parameters. These events of new particle formation involve significant ultrafine particle number concentrations (>104 cm−3 in the size range 3–11 nm) and were observed on 20% of all days, pointing out that a frequent particle production from gaseous precursors can occur despite a relatively high pre-existing particle surface area. The maximum in the observed particle size in their distributions was mostly above 3 nm, suggesting the actual particle nucleation to take place upwind of the measurement site. A particle growth analysis yielded 2.3±1.4 h as an upper limit of the time for the particles to grow from the critical cluster size till the observation of the peak in ultrafine number concentration. On 80% of the significant events of new particle formation (though not on all), SO2 concentrations increased considerably (by an average factor of 7), most likely by entrainment from aloft. Particle surface area was, on average, higher on event days compared to non-event days, indicating only a weak competition between condensation onto the pre-existing particle surface area and the new particle formation process. The highest statistical correlation was found between the events of new particle formation and solar radiation, indicating a high degree of meteorological control


   Experimental and results (warming)

Accurate whole sky ground level manual observations were maintained throughout the 2005 and 2006 period from the author’s home in North Wales and daytime temperatures were also recorded.

The data is summarised below and then specific cases will be discussed in more detail.

Date of trail

 Time to change

T start C

T end C

Rise C

Type of Trails








3 days






3 days




air lane north west


2 days




air lane  north west


3 days




whole sky








4 days




3 days




whole sky









Only data from persistent trials laid down after 8 pm has been used and with the exception of one event in January 2007, mainly data from 2005 and 2006 has been used.  

As can be seen from the table very significant temperature rises are seen on average 3 days after the appearance of night time persistent contrails in the summer months of the two test years.


Discussion of warming results

The case on the 14th of July is interesting because the trails were created in the form of arcs and circles which suggests the activities of either research or military aircraft.   These trails spread into cirrus which produced halos and late night sun dogs just before sunset.  Due to the skewed areal distribution of contrail cirrus perfect sun dogs are rarely created. Those seen are often lop-sided or one sided and very smeared.  Green and pink cloud iridescence was associated with the contrail cirrus formed after the event of March 2005.


The average daytime temperature rise as a result of or coinciding with the trails is a very significant +10c. 


It is tempting to presume these are just the effects of a warm front or warm air sector.   However it is indisputable that the largest change occurs after the invasions of whole sky persistent contrails on 16th July 2006.


The work strongly supports the work of Stuber et al 2005 (5) and the notion that flying at night causes warming.

The result also strongly supports the hypothesis of Meerkötter (1999) (6) and Stuber and Forster 2007 (7).

On the other hand there may be instances where it would be useful to have an element of predictable control over local weather.  The Russians and Chinese would appear to be experts in this type of field, see for example Taubenfeld (1967)(8) , Hoffmann (2002)(9) and  Bolonkin (2007) (10).


Other than basic heat trapping yielding positive climate forcing, explanations for the behaviour of bi-directional climate forcing behaviour of persistent contrails often feature reference to cloud microphysics in terms of ice crystal size and morphology, these are usually fairly short term issues.   Given the time scale of the observed effects here one needs to look at the physical chemistry of what is going on.  Nitric acid and NAT are known to evolve in both the troposphere and stratosphere over the time scales involved (11). Perhaps a process rather like that in PSC causes the warming or perhaps the aerosol is re-absorbed in the troposphere and creates additional natural cirrus causing further warming. 


Experimental and results:  cooling

The results have been acquired and dealt with in a similar manner to these for warming.  More of the cooling events seemed to happen in 2007. The results are shown below:



temp change Celsius

Days to effect

Rain/flood event Y/N










































It is tempting to ascribe cooling to the simple passage of a cold front but the timescales for the effects observed are far too long and should be measured in hours rather than days for the passage of a front.   The average time for cooling to take effect observed here is about 4.8 days.    It is known that immediate surface cooling can happen  by shadow effect  under an optically dense persistent contrail patch (12), longer term cooling could be related to stratospheric ozone depletion.     Lacis  et al  (1990) (13) have described  a simple method for evaluating the radiative forcing of surface temperature caused by changes in the vertical distribution of ozone. Their  method employs a parameterization based on one-dimensional radiative-convective equilibrium calculations; these calculations predict that the surface temperature should warm in response to both decreases in ozone above 30 km and increases in ozone below 30 km.  Ozone changes due to aircraft and persistent contrails are expected to be taking place  below 30 km.   Meilinger et al (2005) (14) have computed the effects of persistent contrails on various atmospheric components and gases including ozone.  They show that tropospheric ozone recovers with 24 h  during a persistent contrail outbreak but stratospheric ozone is still falling even at the end of the second day.  Taken with the method of Andrew and Lacis (13) this would be sufficient to account for the observed drops in temperature tabulated above.      



Flooding events

 Frich et al ( 2002) (15) have noted coherent spatial patterns in such events, commencing in the second half of the twentieth century.    It would seem logical to the present author that there may be a connection here date wise  with the growth of jet aviation and also as world air- lanes operate in similar patterns. 

It also seems logical that increased differential surface temperatures as observed above and particularly of the sea  could intensify convection and bring about pin point flooding events, see for example Lebeaupin, V Ducrocq (16).    However, we also need to understand more about the long range transport of Saharan  dust in this aspect as well, see Chaboureau et al (2011) (17).   The author has noted that the contrail cirrus which precedes flooding events often takes on a very distinctive comb-like appearance.    


Conclusions and Accounting for UK’s changed climate

What appears absolutely clear from the above observations is that aviation would now completely appear to be controlling the UK's weather and local climate in North Wales. There is considerable and very up to date theoretical support for this. It is doubted that these findings are  presently utilised elsewhere and hopefully they will become an asset to  climatologists and weather forecasters not just in the UK but hopefully, the World over.


An extension of the  hypotheses outlined above  is  in that it is  proposed these results could begin to be used to account for the recent changes in UK Climate trends announced by the Met Office.


London and the South East of Britain are officially getting warmer.  North Wales is officially getting much colder.  Quite simply, the former has lots of night flying, whereas North Wales has predominantly daytime flying.   Negative climate forcing is thought to dominate for daytime persistent contrails.


Human kind has often striven to control nature from the days as early as those of King Canute.  It would seem our desire to have more and more global  travel is impacting phenomenally on the World's weather and climate.  Recently Haywood et al (2009)(18) noted that a single aircraft operating in conditions favourable for persistent contrail formation appears to exert a contrail-induced radiative forcing some 5000 times greater (in W m−2 km−1) than recent estimates of the average persistent contrail radiative forcing from the entire civil aviation fleet. In his study he posed the question that there was  the need to establish whether similar events are common or highly unusual for a confident assessment of the total climate effect of aviation.


It would seem from the results and explanations of the work presented above and previously by Barnes (19)  that huge perturbations of weather and radiative forcing by aviation are indeed common as perhaps Haywood feared (by interpretation of the language used).  Thus further it would appear we are inadvertently controlling the weather on a routine almost predictable basis.  


Extra and unsung climate feedback mechanisms involving CO2 and aircraft. 

A final thought relates to new particle events as yet other and unsung negative feedback mechanisms against CO2 induced warming.  Firstly and  simply warming results in more turbulence and turbulence results in more  new particle events, see Wehner and Seiebert  (2010) (20) which if they are in daytime and of the SO2 entrained variety will cause a lot of cooling via the mechanisms described above.     Such new particle events are also enhanced by vertical motion of the atmosphere, see Young  et al (2007) (21). To the present author it seems ironic that a person, although a qualified scientist and engineer, yet one with no formal training  in meteorology or climate science has had to provide the missing links in this highly complex puzzle. It can be only hoped that these findings will be used for the benefit of human kind. Both turbulence and vertical motion are provided by heavy air traffic  so here we have two potential and hitherto totally unsung climate feedback mechanisms.   Another example of this principle is the formation of cloud banks above operational wind farms, see photograph ( Barnes 2013 ) (1).    Vertical motion of aircraft in the atmosphere  is probably far more quantised and less random than it used to be as a result of  AVOSS, AMDAR and satellite based contrail avoidance systems.  This may actually aid the incorporation of these findings into cloud, weather and climate  parameterization models.      


Link with planetary waves

There are known planetary waves with periods of 3–4-days, 6–8-days and 12–16-days  as evidenced by oscillations in the zonal winds, see Takahashi et al (22). Grytsai et al (23) have recorded planetary waves in total Ozone concentration for which  stationary components the amplitudes are 38.3, 4.8, 1.8,1.2, 0.7 DU, respectively.  The figure of 4.8 DU is remarkably close to the 4.8 day average for contrail (ozone) cooling described in this present work.





The author wishes to acknowledge Mr P Van Doorn of TORRO for interesting and stimulating discussions on weather and contrails.  Further the author wishes to acknowledge his wife for coping with the author's apparent but now justified eccentricity in sky gazing.






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© DR CHRIS BARNES 22ND JUNE  2013  -  This work is published on the internet today but anyone wishing to use any part hereof must contact me first.