Contrail (or rather persistent contrail) optical phenomena; a new weather lore, an eight year study. By Dr Chris Barnes, Bangor Scientific and Educational Consultants, e-mail scienceconsultants@yahoo.co.uk - July 2013

Dr Barnes Homepage http://www.drchrisbarnes.co.uk

Abstract

'Traditional weather lore is defined and briefly reviewed. Contrails, persistent contrails and attendant cirrus aviaticus present an opportunity for an investigation of a new type of weather lore (in this case UK based) based on some of the specific and often hitherto rare, no less so, optical phenomena which they bring. The phenomena considered are: White haze, Brown CZA (circum-zenith arc); Smeared sun dogs (often lop sided) containing usually red-yellow end of spectrum only (or brown); Salmon red/teal blue edge iridescence, Pink /green iridescence (also often seen in contrail before it spreads into cirrus); Solar and lunar haloes; ‘Whiter than white’ pink at dusk contrails and Hole punch clouds. It is shown that each of these specific phenomena bring about repeatable changes in temperature and weather type, usually within periods of 0.5 -3 days. Each specific change can be explained by contrail and cloud microphysics. On a more serious note the particular types of iridescence colours, in particular, are indicators of ice crystal size and by using multiple nationwide or worldwide observers it might be possible to get a better handle on the effects of aviation on global climate change on this basis alone and/or inform the use of contrail technology as a less radical method for CO2 offset geo-engineering than some of those possibilities hitherto proposed.

Introduction

Weather lore, a body of informal folklore related to the prediction of the weather, goes back at least to Biblical times. It is in Earth's middle latitudes, between roughly 30° to 60° North and South, that a significant portion of humanity's daily activities take place, also the region where the variations defined by meteorologists as 'weather' take place. Weather folklore, therefore, refers to this mid-latitude region of daily variability. Weather lore concerning the appearance of the sky, the conditions of the atmosphere, the type or movement of the clouds, and the direction of the winds may have a scientific basis and likely can predict the weather. Many weather proverbs are nothing more than familiar rhymes, light-hearted ditties or imaginative contradictions. Some have survived the test of careful observation and scientific reasoning to become reliable guides to coming weather change. Only those sayings which prophesy daily change, usually pertaining to sky appearance, cloud movement or wind change, have any hope of success. Lore involving key dates or anniversaries or suggesting monthly or seasonal change can only be right by chance.

Old weather proverbs and saws have their inception in atmospheric conditions. Properly interpreted, these conditions give accurate information on what is likely to happen in the next few hours. For instance, a red sky means rain or dry weather according to the time of the day it occurs. The principle is based on certain optics and conditions of the atmosphere. Another example: smoke hovering near the surface of the ground indicates heavy moisture in the air. When it ascends straight up there is little likelihood of rain.

David Phillips, Senior Climatologist, Environment Canada [1] has provided a listing of some of the more reliable weather proverbs which are:

The moon and the weather may change together,

But a change of the moon, will not change the weather.

A ring around the sun or moon, means rain or snow coming soon.

When grass is dry at morning light

Look for rain before the night.

Dew on the grass, rain won't come to pass.

Sea gull, sea gull, sit on the sand,

It's never good weather while you're on the land.

When sea-gulls fly to land, a storm is at hand.

Rain before seven, fine before eleven.

Evening red and morning grey, two sure signs of one fine day.

The sudden storm lasts not three hours

The sharper the blast, the sooner 'tis past.

The higher the clouds the better the weather.

Cold is the night when the stars shine bright.

Sound travelling far and wide, a stormy day betide.

When the forest murmurs and the mountain roars,

Then close your windows and shut your doors.

When leaves show their undersides, be very sure that rain betides.

Chimney smoke descends, our nice weather ends.

When the night goes to bed with a fever, it will awake with a wet head.

When stars shine clear and bright,

We will have a very cold night.

When the ditch and pond offend the nose,

Then look out for rain and stormy blows.

Three days rain will empty any sky.

The farther the sight, the nearer the rain.

Rain long foretold, long last,

Short notice, soon will pass.

The sharper the blast, the sooner 'tis past.

If bees stay at home, rain will soon come,

If they flay away, fine will be the day.

The first and last frosts are the worst.

When clouds look like black smoke a wise man will put on his cloak.

A rainbow afternoon,

Good weather coming soon.

A rainbow in the morning, is the shepherd's warning

A rainbow at night is the shepherd's delight.

When the chairs squeak, it's of rain they speak.

Catchy drawer and sticky door,

Coming rain will pour and pour.

The winds of the daytime wrestle and fight,

Longer and stronger than those of the night.

Dust rising in dry weather is a sign of approaching change.

Sun sets Friday clear as bell,

Rain on Monday sure as hell.

No weather's ill if the wind be still.

The squeak of the snow will the temperature show.

When smoke hovers close to the ground, there will be a weather change.

When down the chimney falls the soot

Mud will soon be underfoot.

When the sun shines while raining,

it will rain the same time again tomorrow.

When the wind blows from the west, fish bite best.

When it blows from the east, fish bite least.

If salt is sticky,

And gains in weight;

It will rain

Before too late.

Red sky at night, sailor's delight;

Red sky in morning, sailor take warning.

When clouds appear like rocks and towers,

The Earth's refreshed by frequent showers.

When the wind is in the east, 'tis neither good for man nor beast.

The more cloud types present, the greater the chance of rain or snow.

Persistent contrails are for some a blight of the skies, an omen of climate change, or even perhaps portend of doom? For instance; it is reputed that the Hopi Indians had a saying that 'the end of the world will come when there are 'cobwebs' in the skies' [2]. We could take this to mean contrail lines. Still the end of the World did not come when the Mayan calendar reset recently so perhaps we ought not worry unduly!

For the present author, persistent contrails and their behaviour present both a scientific challenge and a personal fascination. Sometimes they can foul up the sky and make it look downright ugly but other times the ensuing cirrus they generate can not only exhibit truly stunning detail and beauty with shapes akin to DNA helices and even mystical beings like angels and Christ on the cross. From a scientific standpoint they can expose the hitherto unseen gravity wave turbulent motions of the upper atmosphere. Living near mountain ranges one can see the resultant manifold GW diffraction patterns which also occur. Such patterns are often seen from space or by means of radar but rarely from earth until the advent of heavy air traffic. One of the only references/examples I have been able to find to compliment my own observations is at http://www.planetpals.com/weather_phenomena.html [3].

Contrail cirrus or cirrus ‘aviaticus’ as it is sometimes known can either cool or warm the planet depending on the ice crystal size and distribution. These same ice crystals can give rise to some hitherto very rare optical phenomenon not usually seen at mid- latitudes.

Since optical phenomena have been used in the past in weather lore, the purpose of this present work is to explore if the appearance of various types of contrail specific optical phenomena as viewed from earth can used as predictors of changes in local weather type. Persistent contrails or so called contrail outbreaks are usually associated with jet streams, frontal systems and mountain wave clouds, see Nunez (2014) [4]. Recently, I have shown persistent contrails can apparently outbreak in heavy air traffic in the absence of such triggers.

Experimental

For the period 2005-2013 I have kept careful but basic metrological records at my home in Bangor, Wales which is very close to two major air corridors. Days with persistent contrails and unusual optical phenomena have also been logged. I have manually mined all this data in search of predictive relationships with a view to establishing a 21st Century 'contrail weather lore'. The optical effects seen and considered are:

1. White haze

2. Brown CZA ( circum-zenith arc)

3. Smeared sun dogs ( often lop sided) containing usually red-yellow end of spectrum only (or brown)

4. Salmon red/teal blue edge iridescence

5. Pink /green iridescence (also often seen in contrail before it spreads into cirrus)

6. Solar and lunar haloes

7. ‘Whiter than white’, pink at dusk contrails

8. Hole punch clouds

Results

The results are presented below in an easy to understand and self-explanatory table which catalogues the type of weather brought proceeding each phenomenon in terms of precipitation and temperature change and the average time to effect the said change.

Date(s)	Opt. Effect	Weather	Av. T change	Av. Time
		brought	Centigrade	for change days

Apr-13	White haze	Rain	minus 1.5C	2.25 days

Jul-13	Brown CZA	Sun	1.75C	1.75 days
Aug-07	Brown CZA	Sun	2.0C	2 days

10 events	Smeared	Sun	4.2C	2.6 days
2005-2013	Sun dogs

4 events	salmon/teal	Rain	minus 4.25C	2days +/-1day
2005-2013	iridescence

6 events	pink/green	Rain	minus 3.75C	3 days
2005-2013	iridescence


3 events	Haloes	Rain	plus 2.7 C	2 days
2005-2013


14/15/7/2013	ultra white	Fog	minus 10C!	0.5 Day
	pink at dusk


23/02/2010	Hole punch	Mixed	plus 9 C!	1 Day

Discussion

The results for each type of phenomenon are discussed systematically below.

Haze

Haze is often found ahead of cold fronts and contains mainly sulphate aerosol [5]. Sulphate aerosol has a general cooling effect and the mid and low level clouds associated with frontal rainfall will have a considerable cooling effect. The typical time for a frontal system moving in to Britain from the Atlantic is of the order of 3 days, see Peters and Christianson 2002 [6]. Thus the result found here for white haze is elegantly explained.

CZAS and Sun Dogs

CZAS (Circumzenithal arcs) with a 120° parhelion and a 22° parhelion within persistent contrails can occur. These phenomena result from hexagonal plate-shaped ice crystals oriented horizontally with diameters between 300 μm and 2 mm. From observations by Sussmann 1997 [7] and reinvestigation of previous reports, they conclude that a subset of the population in persistent contrails can consist of highly regular, oriented, hexagonal plates or columns comparable to the most regular crystals in natural cirrus clouds. This is explained by measured ambient humidity below the formation conditions of natural cirrus. The resulting strong azimuthal variability of the scattering phase function impacts the radiative transfer through persistent contrails. Zhang et al (2013 ) [8] state that net cloud radiative forcing is positive for most cirrus cloud types unless they have a large number of ice crystals with a dimension <30 microns. Clearly this is not the case when CZAS are observed which accounts for the observed warming which follows. Thus the observation with CZAS is explained.

MI Mishchenko, A Macke - Applied optics, 1999 - opticsinfobase.org [9] state that only particles with with diameters greater than 100–200 μm can become horizontally oriented. Mallmann et al point out that Sun dog produced by plate crystals with their hexagonal faces roughly horizontally oriented. Thus a similar argument on warming to that advanced for CZAS above is relevant.

Cloud Edge effects Coronas and Iridescence

Shaw and Neiman (Applied Optics, Vol. 42, Issue 3, pp. 476-485 (2003)) [10] have used Fraunhofer diffraction theory and meteorological data to determine the nature of cloud-particle distributions and the mean particle sizes required for interpreting photographs of coronas and iridescence in mountain wave clouds. Traditional descriptions of coronas and iridescence usually explain these optical phenomena as diffraction by droplets of liquid water. Their analysis shows that the photographed displays have mean particle sizes from 7.6 to 24.3 μm, with over half the cases requiring diffraction by small (~20 μm) quasispherical ice particles rather than liquid water droplets. Previous documentation of coronas produced by ice particles are limited to observations in cirrus clouds that appear to be composed of small ice crystals, whereas our observations suggest that coronas and iridescence quite often can be created by tiny quasispherical ice particles that might be unique to mountain wave clouds. Furthermore, we see that the dominant colors in mountain wave-cloud coronas are red and blue, rather than the traditionally described red and green.

With the observation of salmon red and teal blue or with pink and green noted on the edges of some of the contrail cirrus in this study, it would appear that such colours are not unique to just mountain wave clouds. This can be explained if droplets or ice crystals of appropriate sizes are available. Sometimes the same pink and green colours are seen in young contrails. I have also witnessed this effect. The available diffraction-corona theory for the interpretation of the cloud iridescence phenomenon has been reviewed by Sassen (1979) ( now only available (mysteriously) at one web site in the WHOLE WIDE WORLD ( light and colour in NATURE) [11] and applied to photographic observations of an iridescent contrail. He concluded that simple-diffraction theory qualitatively explains the occurrence of corona and iridescence under the cloud microphysical conditions with which these phenomena are typically associated, and that the theoretical predictions of cloud droplet diameters of 1–3 µm during initial contrail formation appear to be reasonable for a highly supersaturated environment. In some cases particularly for aerodynamic contrails freezing to tiny crystals occurs very quickly and can lead to persistent contrails and cirrus (Karcher et al) (Kärcher, B., B. Mayer, K. Gierens, U. Burkhardt, H. Mannstein, R. Chatterjee, 2009: Aerodynamic Contrails: Microphysics and Optical Properties.J. Atmos. Sci., 66, 227–243.) [12] These conditions and ice crystals less than about 20 microns in size are likely to lead to environmental cooling rather than warming, see Zhang et al. This is consistent with the falls in temperature observed.

Haloes

Ice crystals of a similar size can also bring about lunar and solar haloes of the type where the moon or sun appears as being viewed through a clear circular hole in a thick sheet. These are much rarer and have only been seen on three occasions during this present study. They were first observed and explained by Sassen et al (1998) Applied Optics, Vol. 37, Issue 9, pp. 1477-1485 (1998) [13]. A high (14.0-km), cold (−71.0 °C) cirrus cloud was studied by Sassesn using ground-based polarization lidar and millimeter radar and aircraft probes on the night of 19 April 1994 from the Cloud and Radiation Testbed site in northern Oklahoma. A rare cirrus cloud lunar corona was generated by this 1–2-km-deep cloud, thus providing an opportunity to measure the composition in situ, which had previously been assumed only on the basis of lidar depolarization data and simple diffraction theory for spheres. In this case, corona ring analysis indicated an effective particle diameter of ~22 μm. A variety of in situ data corroborates the approximate ice-particle size derived from the passive retrieval method, especially near the cloud top, where impacted cloud samples show simple solid crystals. Sassesn et al [13] concluded that the homogeneous freezing of sulfuric acid droplets of stratospheric origin is assumed to be the dominant ice-particle nucleation mode acting in corona-producing cirrus clouds and speculated that this process results in a previously unrecognized mode of acid-contaminated ice-particle growth and that such small-particle cold cirrus clouds are potentially a radiatively distinct type of cloud.

In aviation cirrus it is possible that the aircraft emissions themselves could supply all that is required. Cirrus often forms near the tropo-pause before connective rainfall, see T. J. Garrett et al ( 2004) [14].

Presumably the cloud edge events were experienced before the passage of a cold front hence the fall in temperature and evident precipitation, whereas the haloes were seen before the passage of a warm front hence the increase of temperature into the warm sector.

Pink Contrails at Dusk

Pink contrails at dusk are probably caused by the same phenomenon which makes a red sky. A red sky suggests the atmosphere is loaded with dust and moisture particles which may under anti-cyclonic conditions produce fogs, see for example http://www.loc.gov/rr/scitech/mysteries/weather-sailor.html [15]. Fogs and low clouds are notorious for lowering temperature.

Chinese weather engineers have shown it is feasible to produce artificial fogs covering areas of square kilometres, see http://en.cnki.com.cn/Article_en/CJFDTOTAL-QXKX200704007.htm [16].

Hole Punch Clouds

Heymsfield et al ( 2010) [17] have discussed the production of holes and channels in altocumulus clouds by two commercial turboprop aircraft is documented for the first time. They have provided an unprecedented dataset combining in situ measurements from microphysical probes with remote sensing measurements from cloud radar and lidar operating from the National Science Foundation (NSF)/NCAR C-130 aircraft, as well as ground-based NOAA and Colorado State University (CSU) radars, is used to describe the radar/lidar properties of a hole punch cloud and channel and the ensuing ice microphysical properties and structure of the ice column that subsequently developed. Ice particle production by commercial turboprop aircraft climbing through clouds much warmer than the regions where contrails are produced has the potential to significantly modify the cloud microphysical properties and effectively seed them under some conditions.

They also conclude some jet aircraft may also be producing hole punch clouds when flying through altocumulus with supercooled droplets at heights lower than their normal cruise altitudes, where contrails can form. Commercial aircraft can therefore generate ice and affect the clouds at temperatures as much as 30°C warmer than the −40°C contrail formation threshold temperature. Similar observations have been made by C Westbrook, O Davies - Weather, 2010 - Wiley Online Library.

Heymsfield (2011) [17] also concludes that hole-punch and canal clouds have been observed for more than 50 years, but the mechanisms of formation, development, duration, and thus the extent of their effect have largely been ignored. The holes have been associated with inadvertent seeding of clouds with ice particles generated by aircraft, produced through spontaneous freezing of cloud droplets in air cooled as it flows around aircraft propeller tips or over jet aircraft wings. Model simulations indicate that the growth of the ice particles can induce vertical motions with a duration of 1 hour or more, a process that expands the holes and canals in clouds. Global effects are minimal, but regionally near major airports, additional precipitation can be induced.

In any event any kind of seeding is a hap -hazard operation which possibly accounts for the observation of a mixed local weather type at the time of observation of extensive hole punch type clouds near the author's residence.

It remains unclear as to why there was such a huge increase in temperature associated with the hole punch situation, however, Altostratus decks may be associated with any weather type and in any event this was, unlike most of the other phenomena reported in this study, being only a 'one-off' observation.

Conclusions

The work presented above is useful in two ways. Firstly, it yields a method for the ground observer to predict changes in local weather. Secondly and more seriously the differing optical effects described above will allow ground observers to assess qualitatively and to some extent quantitatively the effects of aviation cirrus and even cirrus in general according to different sizes and shapes of ice crystals which has long been of contention. If a large number of ground observers throughout the country/Europe/the world were to act collaboratively and log their data then doubtless a better understanding of the climate impact of aviation cirrus might be gleaned. The UK Met Office, WMO and NASA ought, perhaps, to look into organising this on a global scale. Perhaps data could be acquired through school and college science projects.

References

1. http://wightdruids.com/index.php?option=com_content&view=article&id=104:weather-lore&catid=40:eisteddfod&Itemid=121

2. http://www.iawwai.com/NorthAmericanProphecies.html

3. http://www.planetpals.com/weather_phenomena.html

4. http://commons.erau.edu/cgi/viewcontent.cgi?article=1009&context=mcnair

5. http://www.spc.noaa.gov/publications/corfidi/haze.html

6. http://www.cmth.ph.ic.ac.uk/people/k.christensen/papers/published/Leipzig.pdf

7. http://worldwidescience.org/topicpages/v/vapor+cirrus+clouds.html

8. http://www.atmos-chem-phys.net/13/4963/2013/acp-13-4963-2013.pdf

9. MI Mishchenko, A Macke - Applied optics, 1999 - opticsinfobase.org

10. http://www.opticsinfobase.org/ao/abstract.cfm?uri=AO-42-3-476

11. http://www.philiplaven.com/links2.html