More Moisture Envelopes

[rpcrowe]

The unusually moist air resulted in some spectacular water envelopes as the jets sped by during the 2010 Airshow at Marine Corps Air Station Miramar, San Diego, California

[Shadowman]

Richard,

Excellent shots, didn't you say that you typically take these photos during the trial runs to avoid the crowds?

[JK6065]

very interesting Richard.
Could you tell some more about these water envelopes? Are these clouds and do they form like that because of turbulence or something?

[ScoutR]

Wow, great shots, I especially like #1 but the second shot is certainly dramatic.

Wendy

[rpcrowe]

Actually I don't shoot during trial runs. I never thought about doing it.

I don't really like shooting this particular airshow because it is usually backlit. There is also a considerable distance between the front row of the spectators to the runway along which the aircraft make their runs probably something like 100 or 150 yards or meters. I don't know the exact distance but it is further than many airshows I have visited. However, I understand that airshows have generally increased the distance between the performing aircraft and the spectators for safety purposes.

As far as the water envelope, I am not sure of the exact physics. Perhaps someone else can tell us? I think that the aircraft flying at high speed turns the invisible moisture in the air into visible water droplets which causes the cloud. It is really quite spectacular.

[Dave Humphries]

I think this is how it works ...

Any moisture in the atmosphere that is normally invisible (except on a foggy day) can 'suddenly' condense under two conditions; a fall in air temperatue or air pressure.

So I believe what happens here is that the dew point; the temperature and pressure that results in dew forming, is only just below the current air temperature and pressure (for the amount of moisture held in the air).

From now on, we'll ignore the temperature aspect as that isn't relevant here.

Aeroplanes fly by generating lift from the wings, which is formed by the speed of the air over the wing being faster than that under it, this reduces the air pressure above the wing, meaning the air below the wing forces it upwards - and well - the plane flies.

Under certain conditions, like these, this drop in air pressure above the wings is sufficient to condense the moisture forming "instant cloud", which evaporates again as soon as the plane's wing has passed. The effect you see, is the wing, or any other bits of airframe generating lift, are cloaked in this mist, which 'keeps up with' the plane.

You often see it even on airliners when they pass through the cloud base altitude on a day with not many clouds.

Not sure I explained that very well

Ooops, nearly forgot to say; good shots Richard,

[Colin Southern]

Hi Dave,

Well done

Keep in mind that if you compress a gas it heats up ... But if you expand a gas is cools down ... And the low pressure area above the wing allows the gas to expand. And as you cool the gas it's potential to hold water decreases ... And so relative humidity increases ... And when it reaches 100% vapor becomes visible ... And puts on a darn fine show for us

[Dave Humphries]

Keep in mind that if you compress a gas it heats up ... But if you expand a gas is cools down ... And the low pressure area above the wing allows the gas to expand. And as you cool the gas it's potential to hold water decreases ... And so relative humidity increases ... And when it reaches 100% vapor becomes visible ... And puts on a darn fine show for us

Very true, I thought I didn't have the whole story straight

From now on, we'll ignore the temperature aspect as that isn't relevant here.

Now I am wondering how wrong this bit is?

[RockNGoalStar]

The second one is particularly incredible!!

What lens do you use?

[Colin Southern]

Now I am wondering how wrong this bit is?

Not sure to be honest ... I think it's a question Sean might be (slightly!) over-qualified to answer! I've always thought of the two as being inter-related.

[rpcrowe]

I shot these with a Canon 40D and a 300mm f/4L IS lens. I used ISO 400 but, could easily (and perhaps should have) used ISO 200 or even ISO 100. I used AV and f/11 but, could and should have used f/5.6. I have one problem when looking directly into the sun. When I do, I have problems reading the exposure information in the viewfinder. I can't use the top LCD either since my eyeglasses are photogreys and they darken too far. I am going to buy a pair of granny half-glasses and wear then on a string around my neck. It may look like an old-lady lilrarian, but at least I will be able to see and read the LCD with exposure information.

[Shadowman]

Actually I don't shoot during trial runs. I never thought about doing it.

I don't really like shooting this particular airshow because it is usually backlit. There is also a considerable distance between the front row of the spectators to the runway along which the aircraft make their runs probably something like 100 or 150 yards or meters. I don't know the exact distance but it is further than many airshows I have visited. However, I understand that airshows have generally increased the distance between the performing aircraft and the spectators for safety purposes.

As far as the water envelope, I am not sure of the exact physics. Perhaps someone else can tell us? I think that the aircraft flying at high speed turns the invisible moisture in the air into visible water droplets which causes the cloud. It is really quite spectacular.

The crowd is why I thought about shooting prior to the actual show. I can't imagine being able to comfortably photograph in a crowd without getting jostled.