A Weather Question...

stormchaser

stormchaser

Well-Known Member
Yesterday while flying south of Dallas-Fort Worth, I noticed something that I frequently see when flying.

It's the layer between the clear skies above and the haze below. Anyone know what that is called?

It often is the area where small clouds develop, and this day was no exception. Perfect visibility on top, this VERY DEFINED LINE (almost like a higher horizon), and terrible visibility (and a different color to boot!) below. Clouds developed throughout the day yesterday on this line, but there was NO vertical development at all.

I notice this "fake horizon" on other days, too, but clouds don't always develop there. BUT if they are going to develop, I know where to find them...right on this line. But it's always a different color on top vs. below (good visibility vs. poor).

Saturation line? Dew point line? I'm trying to trick you into thinking I'm the earth even though I'm not line?

DSC09092.jpg
 
Swen said:
The Wiki knows all.

Inversions appear to act as a 'cap' to convection.
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Yes, there may be an inversion at work sometimes. But heating of the surface also results in air rising just due to buoyancy up to the convective condensation level, which is where you'll see the bases of those puffy clouds that form.

All of that particle-laden air rises and brings the particulate up with it to the CCL, and you get a pretty clear haze line on some days.
 
primate said:
All of that particle-laden air rises and brings the particulate up with it to the CCL, and you get a pretty clear haze line on some days.
Click to expand...

That haze line forms because of the inversion. Rising air cannot pass through the inversion, which causes those molecules to basically hit a ceiling. This is very noticeable in the San Francisco area. Without the inversion those particles keep rising and disperse over a much greater mass of air.

The reason you get the haze line some days and not others is that inversion. Particles rise from convective activity that is at work every single day. The amount present obviously varies from day to day but nevertheless particles will rise from that activity.


Edit: The CCL has little, if anything, to do with this phenomena. All that is is the point where air becomes saturated or the altitude where clouds begin to form. A great example disproving this would be any day where you see cumulus clouds forming, do you typically find haze below cumulus clouds? No, you don't. Yet the base of those clouds is the CCL.
 
Well, in some cases I guess it works that way, I agree that an inversion can result in this effect. But even without an inversion, any rising air reaches a level at which it will rise no further, due to it becoming equal in density and temperature to the surrounding air. And if it is moist air, which it usually is and consequently less dense, at some point (CCL), the moisture condenses and the latent heat of condensation is released in to the surrounding air, exhausting the latent energy in the air parcel, thus ending the rising action. So the rising air carrying the particulates reaches the level of equilibrium and doesn't rise any higher, so no particulates rise.
 
shdw said:
The CCL has little, if anything, to do with this phenomena. All that is is the point where air becomes saturated or the altitude where clouds begin to form. A great example disproving this would be any day where you see cumulus clouds forming, do you typically find haze below cumulus clouds? No, you don't. Yet the base of those clouds is the CCL.
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The original poster said that he sees clouds forming at the same layer as that haze line. How can we account for that then ? Air doesn't condense as it rises to a warmer level as it would in an inversion, so you won't see the cloud bases there in spite of the fact that the overlying air is warmer and moist. It will be higher than the inversion layer.

And ask any glider pilot if there is a level at which you encounter the top of vertical air movement. And that is not dependent upon an inversion.

Hey, I'm from Atlanta, I know from haze.
 
primate said:
The original poster said that he sees clouds forming at the same layer as that haze line. How can we account for that then ?
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Some upward moving particles move quick enough to pass through the inversion. It is typical with a weaker inversion, but still possible with stronger inversions. If you notice the haze layer and false horizon stop and just above that is where clouds form, just past the inversion.

The level where vertical movement stops varies drastically from 1 square mile of land to the next. If you are positioned over a huge square mile of pavement you will see vertical development many thousands of feet higher than that of a square mile of water. So why does an area with unequal heating have one defined horizon layer? There must be something that stops these stronger areas of lift from passing above weaker areas of lift.
 
shdw said:
That haze line forms because of the inversion. Rising air cannot pass through the inversion, which causes those molecules to basically hit a ceiling. This is very noticeable in the San Francisco area. Without the inversion those particles keep rising and disperse over a much greater mass of air.

The reason you get the haze line some days and not others is that inversion. Particles rise from convective activity that is at work every single day. The amount present obviously varies from day to day but nevertheless particles will rise from that activity.
Click to expand...
This is correct. It's one of the few things I remember from Aviation Meteorology.
 
shdw said:
Some upward moving particles move quick enough to pass through the inversion. It is typical with a weaker inversion, but still possible with stronger inversions. If you notice the haze layer and false horizon stop and just above that is where clouds form, just past the inversion.
Click to expand...

That wouldn't account for cloud bases at the same level as the haze. If the air rises to the inversion layer, then if it rises any higher, it will be in warmer air. Water vapor will only condense into visible moisture if the ambient air temperature is at the dewpoint.

Air in the overlying layer such as occurs in a temperature inversion, is warmer than the underlying air. So condensation won't occur at that level. Vertical development such as a cumulus structure will definitely not occur into overlying warmer air, all the condensation action if it even gets started in the lower cooler air layer will halt at the warm air layer.

Inversions are characterized by multiple cloud layers, usually one below at the temp-dewpoint equivalency point, and one higher above the inversion layer as the temperature of rising air parcels once again arrives at the dewpoint level in the higher layer.
 
primate said:
That wouldn't account for cloud bases at the same level as the haze. If the air rises to the inversion layer, then if it rises any higher, it will be in warmer air. Water vapor will only condense into visible moisture if the ambient air temperature is at the dewpoint.
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You are picturing it wrong. Here:

2,000' = 22
3,000' = 21 (inversion start)
4,000' = 22 (inversion top)
5,000' = 19 (no more inversion)

The false horizon here would occur between 4 and 5 thousand feet. Air would begin to slow between 3 and 4 thousand feet from the non standard lapse rate beginning the inversion and would cap somewhere between 4 and 5 thousand feet. Any air particles that made it through to 5,000 feet, under the right conditions, could form clouds just above the inversion. It is very rare to ever see clouds form under an inversion, though it is possible.
 
Um, maybe the haze layer would sneak up into the warmer air layer a bit, can't say for sure. But you did argue that the inversion caps the haze layer, stopping upward air movement cold (no double entendre intended). So that sort of works against your original argument.

And I was mentioning CCL/LCL in an attempt to explain what the o.p. said he observed with cu bases at the haze layer. I can't recall ever seeing that, but hey, I haven't seen everything.

Of course, just in terms of why the air is rising in the first place, that explanation works. I do like your argument of why it is consistently at the same layer over a large area not being explained unless there is an inversion cap. Of course, you see well-defined haze layers in stable wx since the particles aren't disturbed and scattered by wildly varying convective action, implying that the lapse rate is stable across a large area, so you would get the same effect without an inversion cap.

And hey, thanks for helping me work on my post count, and motivating me to study weather for my upcoming glider practical !

Cheers
 
primate said:
Um, maybe the haze layer would sneak up into the warmer air layer a bit, can't say for sure. But you did argue that the inversion caps the haze layer, stopping upward air movement cold (no double entendre intended). So that sort of works against your original argument.
Click to expand...

It wasn't an argument, just trying to explain what you asked. It does stop the majority cold, and I rarely see clouds form above these inversions either though I have seen it. Typically I see them start forming when convective heating is enough for the air to start pushing through the weaker inversions, I will explain this later.

Maybe this will help: Think of the upward flowing air in this fashion for this to make sense picture a large clear bowl of vegetable oil.

Now take vinegar, dye it black, so you can see it, and eye droppers with 3 different water size drops. Remember, particles of air will vary in two ways that can effect their moment and thus how far they can penetrate the inversion layer, size and speed. Take one size of the eye drop and hold it low put a drop in note how far it goes, then higher and note how far, and higher once more. The higher you hold it the more speed you will allow the drops. Then repeat with the larger eye droppers to see the size change. You will notice those drops, will penetrate deeper into the oil just like air does into the inversion.

This requires a very specific day that often doesn't happen when you have inversions, thats why you rarely see it. The dew point of the particles has to at exactly the temperature that occurs just beyond the inversion. However, if you look at days where you find inversions the air is often not very saturated.

They occur typically on with high pressure systems on warmer (I would guess 50-70 degrees F) fall/spring months and select summer months during mid morning up to around noon to late afternoon depending on how hot the day is. Basically, before the sun has time to heat the ground up to the point where thermals break through any inversions thus dispersing the particles. That same sun, on hotter days, evaporates local water sources bringing the moisture needed for those late afternoon showers you see on hotter summer months.

On the hotter days, when the thermals begin to push through the inversion layer, with the now more saturated air from evaporation, is when I see the clouds the OP talks about forming. A couple hours later the haze is gone and out come the big puffy clouds, a few more hours pass and the thunderstorms roll through. Here in NJ we get at least a few days each week from March till October.

Hopefully this helps, I am not trying to say this is the only way it can happen. I am sure there are others, but inversions are certainly the most common. I personally have never heard of another reason for this or read it in any meteorology book I have looked at. That doesn't mean it isn't possible though.
Here is a picture:
316051601_ee82cf7ec8.jpg


Note the clouds in the distance settled on top of the inversion, they appear to be partially in the inversion, but take note that the earth is curved.
 
Not sure if it helps or not, but here are the clouds around 2:00 P.M. on that same day (right on that line). There was absolutely NO vertical development, and it certainly looks like they were "held down."

And here are the specs that day: 65 degrees F on the surface (at 800 feet MSL), 41 degrees F (5C) at 5500 feet MSL (which is the EXACT line of these clouds...where I was flying). Regretfully, I didn't fly any higher, so I don't know if it was warmer above this line or not! That would sure be interesting to know!

Thanks for the info.

DSC09107.jpg
 
That just sounds like a standard sunny day. Sun heats earth, earth heats air, air rises until it is cooled to the same temperature as surrounding air. As air cools it holds less water vapor, water condenses, heating the condensation. This condensation, clouds, will rise slightly higher than dry air until they reach like temp. If there is no orographic lifting or front passing, then there is nothing to cause extensive vertical development.

The math works out almost perfectly. At 800 feet its 65 at 5500 its 41. Thats a difference of 24 degrees through 4700 feet. That is a lapse rate of 5 degrees per thousand feet. Which for drier are is normal. Air stops rising, stops pulling up particles, you have a clearer sky above, hazy skies below.
 
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