Spectacular contrail outbreak over Wellington
On the afternoon of Monday 19 July 2010, a neat set of four persistent contrails moved across the Cook Strait area.
NASA’s MODIS Rapid Response System captured the contrails in the image stream from the Aqua space craft which was over Wellington at about 2:20 pm. You can see the image on the MODIS web site here: http://rapidfire.sci.gsfc.nasa.gov/subsets/?subset=NewZealand.2010200.aqua.1km
Here’s part of the MODIS image.
MODIS Aqua satellite image in true colour at about 2:20 pm 19 July 2010.
Several things to notice:
- There is a contrail in the upper left (labelled NZ152) oriented more or less west-east. I think this was made by Air New Zealand Flight NZ152 which arrived in Wellington at 2:30 pm that afternoon from Melbourne.
- Then there are four contrails oriented northeast – southwest over Marlborough and Cook Strait. These are labelled 1, 2, 3, 4. Contrails 2 (and possibly 4) are casting shadows on the ground and sea. The shadows are labelled 2s and 4s.
- The contrail furthest west (labelled 1) must have come from an aircraft which was on a different route from those that made the other three because it is not parallel with them. This contrail also extends southwest into north Canterbury.
- The two furthest east appear to converge slightly towards the north. I suspect this is because the (westerly) wind was increasing to the south and so the contrails are being rotated anticlockwise a little.
I took some photos of these contrails from the roof of the MetService building in Kelburn, Wellington at 2:45 pm Monday 19 July 2010, just 25 minutes after this MODIS image. Also, MetService’s web-cam at Christchurch Airport caught the southern end of the easternmost contrail (labelled 1 in the MODIS image) as it moved across Canterbury Plains.
Two contrails over Wellington Harbour at 2:45 pm on Monday 19 July 2010. This view is towards the north. One contrail (the eastern one on the right) is partly obscured behind the lower cumulus cloud. These two contrails are the eastern most ones in the satellite image.
These two contrails are the western two in the satellite image. This photo was taken at 2:45 pm on Monday 19 July 2010.
Christchurch Airport web-cam photos looking northeast. This is an animation of images at 10 minute intervals from 2 pm to 4:40 pm.
Around Wellington, the wind at the level of the contrails was quite a strong westerly, which explains why the contrails moved quickly across the sky from west to east. The wind in the atmosphere was also increasing with height; this spreads the contrails out enough to make them visible in satellite images. These contrails could still be seen in a lower resolution infra-red satellite image at 5:00 pm when they were 230 km east of Wellington.
In New Zealand, the long distance air routes are all more or less northeast – southwest. Thus, it is easy to see how several aircraft travelling these routes can create a set of parallel contrails. In Europe and North America the air routes are in all directions, and regular grid patterns of contrails are sometimes seen. Sometimes, the contrails in these grid patterns spread out to form a big sheet of high cloud: cirrus or cirrostratus.
This was one of the best and most persistent contrail outbreaks I have observed for some time. Contrails are interesting to watch and sometimes, as with these, there are fascinating details and patterns in the ice clouds as they evolve.
Keep watching.
Hi,
Is it possible to view the Metservice Christchurch (and others?) webcam online? I also heard that Metservice have/are getting some SnapitHD webcams, will they be available online to the public?
Hello zakalwe,
We have webcams at Christchruch, Dunedin and Hamilton Airports. They were installed for the benefit of our aviation forecasters, so the field of view is of the sky in a certain direction. We intend to install them at other airports… Paraparaumu will be the hot spare, and proabaly others.
The images are not yet available on our web site but we appreciate the interest and we are looking into it now.
They are pretty nifty units; they have an IR mode night time. I don’t know about SnapitHD webcams – we have installed these M12D systems http://www.mobotix.com/other/file/51870/mx_m12d_outdoor_en_200.pdf
“These are not the ‘droids you’re looking for.”
Good work Ross!
These were shot on the same day over kaikoura looking over the ranges.
Mind the chemtrailer comments.
http://chemtrailsoverkaikoura.ning.com/photo/photo/slideshow?albumId=4744723:Album:3355
Thanks RAC,
No, the pilot didn’t forget his lunch, or leave his dog in the car. Too funny!
Christchurch had unexpected fog which closed the airport from about 8:30 AM. Those would be two flights that departed from Auckland and had to divert back there when they learnt of the fog development. The fog eventually cleared at about 1 PM. The other flight further west is probably to Queenstown. They often take that route.
I am pretty sure other photos of this persistent contrail outbreak will turn up.
[...] · Leave a Comment Spectacular contrail outbreak over Wellington Written by Ross Marsden on July 26th, [...]
Hello Northland New Zealand Chemtrails Watch,
Thanks for the reference from your interesting site.
I’m fairly certain that these are contrails. Look, I’ll go way out on a limb here and state as a fact; these are contrails.
Hi Ross, I would like to learn more about what you call “satuarted with respect to ice”
This subject interests me greatly any help would be much appreciated.
Thanks.
Here is a very good video of these contrails over Nelson on the 19th.
RAC, this is a great find! Wow!
I am so impressed by the interest that people are showing in meteorology, aviation and the environment. People in Northland, Nelson, Kaikoura. I would not be surprised, now, if at least one video turns up from Canterbury or Taranaki from that day.
And it’s easy to share all the information now. There is excellent quality, low cost consumer photographic equipment available; there are Internet facilities and services like YouTube, WordPress, and NASA’s excellent MODIS satellite imagery. All this was just not possible 10, 15 years ago.
And the science behind these clouds is easily accessible too: you only need to Google contrail formation, and there it is.
Thanks, RAC. I will answer your question about saturation with respect to ice later this morning… if all goes to plan.
Saturation with respect to ice…
Chris wrote about saturation a while ago.
In the penultimate paragraph, he talks about the situation where water vapour has access to liquid water and an equilibrium being reached between water molecules evaporating and condensing. When there is equilibrium in that water-vapour situation, the air is said to be saturated with respect to water. We are usually talking about the water-vapour situation so we not explicitly say “with respect to water” all the time.
Saturation is expressed as a pressure; actually the partial pressure of water vapour – that part of the total pressure that is exerted by the water vapour component of the air mixture. The saturation vapour pressure only depends on the temperature. The relative humidity (RH) is the ratio of the actual vapour pressure to the saturation vapour pressure of the air. So, if the vapour pressure is half of the saturation vapour pressure at some temperature, then the RH is 50%. This is why the RH is so dependent on temperature.
If there is no water present where the air is becoming saturated, for condensation to occur there needs to be some condensation nuclei. The earth’s atmosphere has an abundance of condensation nuclei consisting of smoke particles (from vegetation burning and volcanoes), salt particles (from ocean spray), and dust. Because of this abundance, condensation occurs in the atmosphere at saturation with no trouble at all. Without these nuclei very high supersaturation would be needed before what is called homogeneous nucleation and spontaneous condensation occurs.
What about ice, then?
The situation with ice is much the same as with water except that we are working at temperatures below freezing, and we are considering equilibrium in the exchange of water molecules between the solid phase (ice) and vapour. The latent heat of vaporisation from the solid phase is higher than that from liquid, so obviously (well, I hope it’s obvious!) the saturation vapour pressure with respect to ice will be different – in fact it is lower. See Clausius-Clapeyron equation for why that is so. Note that this relation is non-linear – that makes it interesting in a mixing situation (which is a linear process) such as exhaling on a cold day, advection or mixing fogs, and contrails.
Again, for deposition to occur, there needs to be freezing nuclei. In our atmosphere there is a veritable dearth of freezing nuclei – there is almost none (apart from ice itself) – and this is why there can be large volumes of the atmosphere (often the upper tropopause) that where the air is so moist that it is super-saturated with respect to ice (and cloud free), but not so moist that it is saturated with respect to water (and cloudy).
How did these regions get like this? Simply by being cooled; by long slow gradual upward motion (and thus cooling) usually upstream of a depression, or on the equator-ward side of polar or subtropical jet streams.
It is in these ice-supersaturated regions that persistent jet-exhaust contrails are found, and it is also where aerodynamic contrails can form.
This has been a long reply. The reward for reading it is to find the link to an excellent recent (and controversial) example of an aerodynamic contrail. Enjoy.
Thanks Ross, you can see why a pressure drop on the upper trailing edge of a wing has the influence it does in the formation of aerodynamic contrails.
You would have to be a right Crakka to think this is chemical being sprayed from a nozzle.
The biggest drop in pressure is over the main part of the wing, not the trailing edge. See:
Airfoils and Airflow and this good Wikipedia entry about aircraft wings.
You might very well think that; I couldn’t possibly comment.
Thanks for clearing that up Ross. I’m allways happy to learn from people that are more intelligent than myself in the field I’m inquiring about.
Certain facts in my article above have been questioned by a member of the exclusive Mysterious New Zealand forum.
In a post on Friday 6 August 2010, Senior Member raupaka quotes me saying, “There is a contrail in the upper left (labelled NZ152) oriented more or less west-east. I think this was made by Air New Zealand Flight NZ152 which arrived in Wellington at 2:30 pm that afternoon from Melbourne.”
Then he says, “buzzzzzzzz … wrong! He is usually quite pedantic about information – or, he pretends to be. I watched that trail forming … it was heading westward. If he had taken a closer look at the trail itself he could have determined direction … or, he could have checked out the flights … but, he didn’t. Tsk Tslk. Some folk would have us believe anything … sheeeez, I dunno!!”
At the time, I used some contacts in the travel industry to find out what the trans-Tasman movements were from Wellington. Now, to check this more carefully since it is being questioned, I obtained the international movements at Wellington Airport that day, Monday 19 July 2010.
Here are all the westbound flights to Australia from Wellington; the times are in NZST:
6:00AM NZ151 to MEL A320
6:00AM QF118 to SYD B737-400
6:45AM NZ145 to SYD A320
7:15AM DJ67 to BNE B737
3:00PM QF38 to MEL B737-400
3:35PM NZ163 to BNE A320
4:05PM QF48 to SYD B737-400
The morning ones are all too early for that MODIS image which was obtained at 2:20PM, and the afternoon ones are too late. Any contrail they produced would not be in a sattelite image aquired at the time this one was. So that east-west contrail could not be from any of these westbound aircraft.
Here are all the eastbound flights to Wellington from Australia on 19 July 2010:
12:05AM NZ166 from BNE A320
2:00PM QF47 from SYD B737-400
2:30PM NZ152 from MEL A320
2:35PM NZ142 from SYD A320
3:10PM QF37 from MEL B737-400
11:20PM DJ68 from BNE B737
11:55PM DJ56 from SYD B737
11:59PM QF117 from SYD B737-400
The only plausible candidates are QF47 or NZ142 from Sydney, or NZ152 from Melbourne. The alignment of the contrail is consistent with it being from the Melbourne flight. The arrival time of the Melbourne flight is consistent with the trail being captured in that MODIS image.
The appearance of parts of a contrail in satellite image is more dependant on the amount of wind shear affecting those parts than their relative age. Since we don’t know much about the wind structure out there, and in particular how it may vary along the trail, nothing can be deduced from the trail’s appearance about the direction the aircraft was travelling.
I think that’s pedantic enough. I’m pretty sure that the east-west trail is from NZ152.
Senior Member raupaka has replied to my comment immediately above…
http://www.mysteriousnewzealand.co.nz/forums/viewtopic.php?p=9822#9822
… and humbly apologised.
Apology accepted.
About determining the contrail direction from its appearance:
raupaka disagrees with my paragraph above about this where I said, “The appearance of parts of a contrail in satellite image[s] …” etc.
The relative age of the ends of a contrail can only be judged from spreading (alone) if you assume that the wind shear is the same all the way along.
Determining direction from the progression of diffusion is another matter. The rate of diffusion will be more or less the same all the way among, and at any point the amount will depend on the age.
Diffusion cannot be observed in satellite images; from the ground it is readily assessed and a direction determination can usually be made from such observations, as raupaka says.
My comments in my previous comment only apply to satellite observations.
I hope this is clear enough now.