I snapped this photo a few days ago. You will see a contrail zipping across the bottom of the picture. It was a day when the sky was slashed with contrails.
There were some interesting cloud formations too. This vertical cloud (intersecting the horizontal contrail) looks like a contrail from an aerobatic airplane. I liked how it hung there suspended.....like a big piece of unravelled toilet paper!
My question is the title - why are contrails more vivid some days?
Psychrometrics or psychrometry are terms used to describe the field of engineering concerned with the determination of physical and thermodynamic properties of gas-vapor mixtures. The term derives from the Greek psuchron (ψυχρόν) meaning "cold"and metron (μέτρον) meaning "means of measurement
Although the principles of psychrometry apply to any physical system consisting of gas-vapor mixtures, the most common system of interest is the mixture of water vapor and air, because of its application in heating, ventilating, and air-conditioning and meteorology. In human terms, our comfort is in large part a consequence of, not just the temperature of the surrounding air, but (because we cool ourselves via perspiration) the extent to which that air is saturated with water vapor
... and on a similar note, how can it be that an airliner at cruising altitude can produce no trail at all?? It's rare, but I've seen this a few times, and it implies that the air for some reason despite the altitude is above freezing so that water in the exhaust is not condensing to form a trail.
Jet engine contrails can show whether it will rain
Paul Simons: Weather Eye
Why can you see your breath on a cold day? The air from your lungs is warm and moist and when this meets the cold air outside it condenses – the invisible water vapour in your breath turns into water droplets and makes a small cloud. The same happens when your breath fogs up a cold bathroom mirror or a cold windscreen in a car.
The same sort of thing explains how white streaks of clouds are left behind from highflying aircraft jets. These contrails are produced by jets at altitudes above about 8km (5 miles). The water vapour that shoots out of a hot jet engine exhaust hits the cold air outside and condenses into a ribbon of cloud. Because the air at these altitudes is so cold, generally less than minus 40C (-40F), only a small amount of liquid is needed for condensation before it freezes into ice crystals.
Contrails can give clues to what the weather will bring. A lack of any contrails from the aircraft is a sign that the high altitude atmosphere is very dry and the weather could stay fine. Short contrails that disappear quite quickly are indicate that the air is fairly moist. And a persistent contrail shows that the air is very moist and possibly a sign of an approaching weather front and rain.
QUOTE] how can it be that an airliner at cruising altitude can produce no trail at all?? It's rare, but I've seen this a few times,[/QUOTE]That was happening overhead today as the transatlantic traffic passed overhead, some were producing short trails, others none at all. There was a clue of course. The westbounds were producing contrails. Eastbounds were not.
My simplistic understanding is that contrails are formed when temperatures fall below minus 40C. Clearly today the westbounds were flying just inside that temperature range and the eastbound flights were outside it.
Obviously it's never as simple as that and the Times article mentioned moisture content of the air. Clearly that's another factor. Interestingly it was a cold crisp day here on the ground which appeared to point to lower moisture content. A quick check revealed a nice spread between the temperature and a very low dewpoint at the nearest big airport. Which appears to confirm my junk science hypothesis.
It was a beautiful day for flying which is all the more puzzling because my last day of the flying season was cancelled for bad weather???????????
Also, the number of contrails I saw when I first left India astonished me. That's when I realised the impact of what I'd always read as "hot-and-high" conditions in the subcontinent. I figure it's (relatively) hot even at that altitude in all but winter. And for most parts of India (Bombay and southwards) "winter" is at worst 15 degrees above zero on the ground.
It depends what we are putting in the mix down the chem plant. Since we started outsourcing a lot of the production to India & China we've had a few issues with quality control due to the inspectors being downsized and outside auditors are corrupt - we've been really worried the mix might not be up to strength. Anyway we've been spraying a bit more until the % strength is back to what it should be. If that batch that was bright red had got out though man - there would have been quite a palaver!