Cloud formation tutorial.

[Furcifer]

Oh spare us - it's of almost no consequence at all other than shifting the dew point a tad.
and how would it ever apply to a clear air convection cell.

lol, now the greenhouse effect is almost of no consequence at all?

Given the topic is cloud formation factors that influence them might be "of consequence".

 

[MRC_Hans]

I think you overlooked and important part of this process, the absorption of infrared radiation by the cloud itself. I'm not sure if this was a deliberate part of the simplification or not?

Frankly, while this plays a sometimes important role, it is not central to the life of clouds. I also omitted the several different starting mechanisms.

"A simplistic explanation is that as the amount of heat energy is spread over a bigger volume, the temperature must fall."

This sentence seems awkward. I'm not sure why,perhaps it's just me.

It is a little blocky. Could you suggest a more elegant way to say it?

Just a little, hopefully constructive observations. An interesting explanation none the less.

Yes, thank you. I do consider putting it on my website, so suggestions for improvements are welcome.

Hans

 

[MRC_Hans]

I don't want anyone to bump this old thread (for obvious reasons), but it is interesting to say the least. I'm not sure if I really received a good answer about what causes that type of cloud formation. I'd like to hear what Hans thinks about it.

I think there is a good explanation in the thread. My knowledge of all this is that of an interested amateur. A former yachtsman, a solid basis knowledge of meteorology has been useful for me. Add to this the fact that I live in a country where the weather is notoriously unstable, then a generalist understanding of weather mechanisms helps you to know what to expect from the skies.

Hans

 

[MRC_Hans]

One note that might be added - thermals on a quiet day will often release in bubbles of hot air.

If the thermal column has a good source well heated by the sun say a parking lot the thermal will stay in place as long as there is sufficient sun.

In many cases tho the "bubble" releases and there is little or no flow from the ground but the process described of expansion and heat/energy conversion goes on regardless that the initial source is cut.

In my corent of the world, on a windy summer day, we often see 'could straits'; lanes of cumulus clouds, alternating with lanes of blue sky. The coud lanes follow the wind, so depending on your position, just a few miles apart, you may experience either a cloudy or a sunny day.

When seeing this on a sattelite photo, the mechanism becomes obvious: some spots in the landscape keep producing thermal bubbles, which, now self-sufficient, drift with the prevailing wind, producing a long line of clouds.

Hans

With an inversion layer, this process is stalled and the longer the inversion remains in place the more violent the energies when the thermals finally breakthrough.

So the end of a hot spell can often be the beginning of violent weather.
But its a good description of the energy transforms.

And those fluffy white clouds that look so innocent from below are boiling cauldrons of wind shear and lift and sink when you get up close and personal in a sailplane or light plane.....and a big enough brute even the heavies fly around.

It's wild in a turbulent thermal near cloud base - the energies are phenomenal.

When a big one goes skyward into a cumulonimbus with the anvil top....all mortals beware - Zeus is in foul mood.

Supercells can drive upwards to 40,000' and are an expanded version of what was so well described in the OP.

http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/supercell.rxml?hret=/guides/mtr/cld/cldtyp/vrt/cb.rxml

As the cloud expands at the thermocline the solar energy to the ground is reduced or cut off....all the sailplanes fall out, the clouds disperse after a bit, the ground warms and away the cycle goes again.

Much fun.....and very chilly at the thermocline which is marked by the cloud base...which is just the visible top of a cell process as a combination of temperature, moisture content and pressure combine to make the cloud form in a visible manifestation.

The same cell process tho can be in place with no visible cloud formation at the top.[/quote]

 

[macdoc]

In my corent of the world, on a windy summer day, we often see 'could straits'; lanes of cumulus clouds, alternating with lanes of blue sky. The coud lanes follow the wind, so depending on your position, just a few miles apart, you may experience either a cloudy or a sunny day.

Yes those are cloud streets in sailplane speak and a lovely thing to cruise along under.

I was in a Lark at about 7,000 feet cruising at 100 knots straight line and not losing any height and got bombarded by Monarch butterflies using the same highway. Memorable flight.

The cloud cover - or lack there of is called cycling in gliding circles and days can go through a number of cycles especially in June in the N Hemisphere.

The prevailing winds end up aligning the thermals with sink areas in between.
That is always going on but it's spotted instead of striped...

 

[TjW]

Actually yes it does. LCL is an approximation based on the initial relative humidity. As the cloud gains sensible heat (my mistake, earlier I said latent) from the incoming radiation the cloud base rises.

Certainly as the atmosphere warms cloudbase rises. It's generally higher in the afternoon.
Have you actually spent much time at cloudbase? If what you propose is true, then older cu would generally have higher bases. This isn't observed.

The bottom of the cloud is warmer than the top. If it wasn't, there wouldn't be a cu. There would be an inversion layer.

You need to describe a method of heat transfer that will move this absorbed sensible heat against the temperature gradient to delay condensation until the air reaches a higher altitude.

 

[macdoc]

You need to describe a method of heat transfer that will move this absorbed sensible heat against the temperature gradient to delay condensation until the air reaches a higher altitude.

exactly
and it's bloody freezing at thermocline on most occasions....

Some good information to lead to comprehension here

http://www.gliderpilot.org/WeatherThermalSoaringForecasts

from that site

On many days of course cumulus clouds form. So, how do we know if they will form, and if so, at what height? One way is simply to click the bottom right end of the sounding on the FSL site and see where the black line appears: If it is to the right of the temperature lapse curve cu will form, if to the left, they will not. The problem with this approach is that the RUC generally performs more poorly in forecasting surface DP's than do the various MOS forecasts or Accuweather and this frequently leads to botched cumulus forecasts. I prefer make use of either MOS or Accuweather T and DP forecasts. I take the difference in forecast surface DP and T (both in Fahrenheit), divide that difference by 4.4, then multiply the quotient by 1,000 to get the height of the cumulus cloudbase (AGL!) in feet:

CLOUDBASE = ((T - DP) / 4.4) * 1,000 FT.
​

If that number is less than the height of the top of the BL cu will form, if greater, they will not. If close, it's a tossup.

and here

http://www.aviationweather.ws/095_Thermal_Soaring.php

This last one is soaring oriented but is very good for diagram and visuals of cumulous and thermal activity.

On point from that link

Depth of Convective Layer (Height of Thermals)

We know that for air to be unstable, the existing lapse rate must be equal to or greater than the dry adiabatic rate of cooling. In other words, in figure 161, the solid black line representing the plotted existing lapse rate would slope parallel to or slope more than the dry adiabats. Obviously it does not. Therefore, at the time the sounding was taken, the air was stable; there was no convective or unstable layer, and thermals were nonexistent. Thermal soaring was impossible.
Now assume that the sounding was made about the time of sunrise. Surface temperature was 59° F (15°C). As temperature rises near the surface during the day, air in the lower levels is warmed and forced upward, cooling at the dry adiabatic rate. Convection begins in the lowest levels. By the time the surface temperature reaches 80° F (about 27° C), convection lifts the air to the level at which it cools adiabatically to the temperature of the surrounding air at 5,000 feet. The existing lapse rate now becomes dry adiabatic from the surface to 5,000 feet and follows the dashed line from the surface to that level. Surface elevation is 2,000 feet ASL; so the convective layer is now 3,000 feet deep. Thermals exist to 3,000 feet above the surface, and low-level soaring is now possible. Above 5,000 feet the lapse rate still is essentially unchanged from the initial lapse rate.
Maximum Height of Thermals

Let's further assume that maximum temperature forecast for the day is 90° F (about 30° C). Plot 90° F at the surface elevation and draw a line (the dashed black line) parallel to the dry adiabats to the level at which it intersects the early morning sounding. This level is 13,000 feet ASL. The convective layer at time of maximum heating would be 11,000 feet deep and soaring should be possible to 13,000 feet ASL. The existing lapse rate in the heat of the day would follow the dashed line from the surface to 13,000 feet; above 13,000, the lapse rate would remain essentially unchanged.
Remember that we are talking about dry thermals. If convective clouds form below the indicated maximum thermal height, they will greatly distort the picture. However, if cumulus clouds do develop, thermals below the cloud base should be strengthened. If more higher clouds develop than were forecast, they will curtail surface heating, and most likely the maximum temperature will be cooler than forecast. Thermals will be weaker and will not reach as high an altitude.

Cumulous are very ephemeral - average joe looks up on a fluffy cloud day - most look the same as if they endure....glider pilots look up and see a very different landscape with cus in various stages of forming and dying and that cycle can be just a few minutes long.

There is simply no time for absorption of any meaningful amount of solar from cloudtop to be useful.

A big cumulo-nimbus might but the energies in that dwarf any minor solar gain. We're talking about nuclear weapon energies.

The average thunderstorm releases the energy equivalent of a 20 kiloton nuclear weapon, or a small nuclear power plant.

This should give people an idea of the energies being dealt with in these processes.

Let's start with hurricanes, with their low-pressure "eye" and multitudes of thunderstorms spinning around it. You probably know that these large tropical cyclones are releasing a lot of energy. But how much is a lot, really?
Well, that depends on how you measure it, but any way you slice it, hurricanes release a phenomenal amount of energy. If we start by looking at just the energy generated by the winds, we find that for a typical mature hurricane, we get numbers in the range of 1.5 x 10^12 Watts or 1.3 x 10^17 Joules/day (this is according to the Atlantic Oceanographic and Meteorological Laboratory.)
This is equivalent to about half of the total electrical generating capacity on the planet! For a single hurricane!
But that's not all, we're just getting started. A hurricane also releases energy through the formation of clouds and rain (it takes energy to evaporate all that water). If we crunch the numbers for an average hurricane (1.5 cm/day of rain, circle radius of 665 km), we get a gigantic amount of energy: 6.0 x 10^14 Watts or 5.2 x 10^19 Joules/day!
This is equivalent to about 200 times the total electrical generating capacity on the planet! NASA says that "during its life cycle a hurricane can expend as much energy as 10,000 nuclear bombs!" And we're just talking about average hurricanes here, not Katrina.

http://dsc.discovery.com/energy/energy-power/volcano-waterfall-thunderstorm-energy-stats-02.html

When you are up close to a strong cell in a 300 kg aircraft....well you feel damn insignificant

and noodling about solar gain on the beast .....not much point.

 

[MRC_Hans]

Yes those are cloud streets in sailplane speak and a lovely thing to cruise along under.

I was in a Lark at about 7,000 feet cruising at 100 knots straight line and not losing any height and got bombarded by Monarch butterflies using the same highway. Memorable flight.

The cloud cover - or lack there of is called cycling in gliding circles and days can go through a number of cycles especially in June in the N Hemisphere.

The prevailing winds end up aligning the thermals with sink areas in between.
That is always going on but it's spotted instead of striped...

Ahh, cloud streets. We call it that in Danish, also (skygader), I just thought it would be too easy to make a direct translation.

To 3bodyproblem: Of course absorbtion of sunlight adds to the energy in a cloud, but it will not change the cloud base, because it will only act higher up in the cloud. It might change the point where freezing occurs, though.

Of course, as the whole landscape, including the air over it, heats up during the day, the cloud base will tend to rise because the RH falls.

You must realize, however, that the cloud base is a very dynamic place; it is really just the zone in the rising column of air where condensation starts.

Hans

Hans

 

[This is The End]

By cause do you mean "a plane flew through the layer of clouds", or do you mean some more detailed description of the behavior of the water droplets?

Well, "planes fly through a layer of clouds" all the time and that basically never happens. So, yes, I do mean a (bit more) detailed description of what is happening in the example linked to in post #4. (I will explain further below).

I think there is a good explanation in the thread. My knowledge of all this is that of an interested amateur. A former yachtsman, a solid basis knowledge of meteorology has been useful for me. Add to this the fact that I live in a country where the weather is notoriously unstable, then a generalist understanding of weather mechanisms helps you to know what to expect from the skies.

Hans

I assume you are referring to this (since it was the only explanation given):

The foundation of a hole punch cloud is traditionally a mid- or high-altitude cloud type such as cirrus or cirro-stratus. Such clouds generally form above 20,000 feet or so in the atmosphere. The National Weather Service has explained that such clouds are frequently composed of both ice crystals and super-cooled water droplets – water that is below the freezing temperature but still exists in liquid form. When such a delicate balance occurs, only a slight disruption of this delicate balance may lead to a striking result....(snip)...It is believed that a cloud may be disrupted in this manner when a a jet flies through the thin cloud layer. Such a disruption may spur the quick freezing of liquid droplets and evaporation of other droplets. This would create the void in the space in which the jet passed through the layer.

While the source of hole punch clouds may be somewhat uncertain, they are certain to cause quite a vigorous discussion.

So, would it be the exactness of the conditions (particularly the amount and temperature of the droplets) that makes this such a rare event?

This situation reminds me perfectly of the Snap Freezing lake thread from a few months ago.

Both very rare, same conditions required, etc.

Still, when I watch the video of the cloud, it just doesn't seem like a plane would be the cause... Perhaps I am thinking it would require something going more directly downward (and faster? hotter?) than a plane, like a meteor or space debris. It would make more sense for a small disturbance to expand outward in that case.

Also note that after that (very reasonable) explanation they added "the source of hole punch clouds may be somewhat uncertain". As if they were also not quite sure (even less than you would assume normally).

 

[Furcifer]

To 3bodyproblem: Of course absorbtion of sunlight adds to the energy in a cloud, but it will not change the cloud base, because it will only act higher up in the cloud. It might change the point where freezing occurs, though.

Of course, as the whole landscape, including the air over it, heats up during the day, the cloud base will tend to rise because the RH falls.

You must realize, however, that the cloud base is a very dynamic place; it is really just the zone in the rising column of air where condensation starts.

Hans

Hans

The absorbed radiation radiates in all directions so I'm not convinced that it doesn't change the cloud base. Not by very much however, it appears to be only a small part of the error in the calculations. I wasn't able to find out how the absorbed radiation affects moist convection in the literature either. Long story short it is a very dynamic place and the absorbed radiation doesn't have as much effect on the formation of cumulus clouds as I had stated earlier.

 

[MRC_Hans]

Still, when I watch the video of the cloud, it just doesn't seem like a plane would be the cause... Perhaps I am thinking it would require something going more directly downward (and faster? hotter?) than a plane, like a meteor or space debris. It would make more sense for a small disturbance to expand outward in that case.

Also note that after that (very reasonable) explanation they added "the source of hole punch clouds may be somewhat uncertain". As if they were also not quite sure (even less than you would assume normally).

I would think that any disturbance of reasonable magnitude could be the cause. Since planes are much more common than the other possible causes, that is a good assumption. Don't get fooled by the nice round appearance of the phenomenon, that is because the effect spreads in all directions, creating a round hole. All this happens at some 30,000ft, so the holes we see in the photos are maybe 5 miles across.

Perhaps, but remember, I'm just speculating, a thermal bubble reaching the layer could also trigger the hole. In that case, the thermal would sort of collapse dur to the sudden influx of ice crystals and fall back.

Hans

 

[This is The End]

I would think that any disturbance of reasonable magnitude could be the cause. Since planes are much more common than the other possible causes, that is a good assumption. Don't get fooled by the nice round appearance of the phenomenon, that is because the effect spreads in all directions, creating a round hole.

Well, it wasn't really the shape that doesn't sound right, but the trajectory.

All this happens at some 30,000ft, so the holes we see in the photos are maybe 5 miles across.

I tried to work out the size of the hole from the video and realized it's a crap-shoot.

Perhaps, but remember, I'm just speculating, a thermal bubble reaching the layer could also trigger the hole. In that case, the thermal would sort of collapse dur to the sudden influx of ice crystals and fall back.

Hans

Yeah, something like that sounds a bit more plausible.

 

[macdoc]

Weird events happen over heat sources at night with the lighting etc.

Clear air - we swore it was a pulsing red/orange UFO - actually made the hair on the back of my neck stand up it was that good an illusion.

Turned out to be a night time still air thermal generated by a chemical plant in Sarnia and underlit by the gas flares below so the whole baby cu glowed and pulsed. Perfect symmetry.

Relieved laughter as we circled our "UFO"

Clouds and weather layers can get very weird.

Some good one here
http://www.crystalinks.com/lenticular.html

Mountain wave effects can occur far far away from the mountains depending on wind strength, direction and as always the humidity/temp gradient at the time.

Bring refracted/reflected light into play and some weird things come into view. Toss in a CME event