Why do clouds float??
WWWgraphix
Peter Rye
wwwgr...@aol.com (WWWgraphix) wrote:
>Do clouds float due to some sort of "kite" effect? Or??
They don't float. Their droplets are so small that they sink only
slowly.
Jacques Marcoux
wwwgr...@aol.com (WWWgraphix) writes:
>
> Do clouds float due to some sort of "kite" effect? Or??
> TIA
.. Now I think I just reached the state of HYPERTENSION that comes
JUST BEFORE you see the TOTAL at the SAFEWAY CHECKOUT COUNTER!
Justin Reedy
there were more than enough people on this newsgroup that were more
qualified to answer that I am. I'm just an undergrad Earth and
Atmospheric Sciences major, so cut me a little slack if I mess this stuff
up. Here goes-->
Clouds form when a parcel of air is lifted to a higher altitude and the
water vapor in the air is cooled to the point where it condenses and
coalesces, forming a cloud. After the water condenses, the parcel of air
cools at a different rate that normal (Wet adiabatic rate as opposed to
dry adiabatic rate). When air is defined as unstable, the parcel of air
cools slower than the surrounding air, and at a certain point can begin
rising under its own power, creating clouds with vertical development.
Cumuls clouds are an example of this. If the rising and expanding
continue, a Cumulonimbus cloud can form (big, towering cloud with anvil
head). So, actually, Clouds do float, contrary to what some guy said. I
think. Hope this helps.
Justin S. Reedy
Georgia Instiute of Technology
gt3...@prism.gatech.edu
--
Justin Sullivan Reedy
Georgia Institute of Technology, Atlanta Georgia, 30332
uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!gt3811b
Internet: gt3...@prism.gatech.edu
Raymond Sirois
On 20 Dec 1996 17:21:35 -0500, gt3...@prism.gatech.edu (Justin Reedy)
wrote:
Having stepped into the middle of a thread, I may be placing my foot
firmly in mouth, but here goes anyway. The original question was Why
do clouds float? The answer, simplistic as it may sound is this:
Clouds are a visible manifestation of a parcel of air that is
saturated with water vapor. Moist air is less dense than dry air.
Clouds float, therefore, because they are less dense than the dry air
below them. They don't rise above a certain level because at some
point the air above the cloud is less dense than the air within the
cloud. Clouds which are forced aloft due to strong thermal forces are
the exception to this GENERAL, and SIMPLISTIC rule...
Ray
Chuck Doswell
In article <32bc126b.6460168@news-server>, rsi...@elmira.twcable.com
(Raymond Sirois) wrote:
> On 20 Dec 1996 17:21:35 -0500, gt3...@prism.gatech.edu (Justin Reedy)
> wrote:
>
> >>wwwgr...@aol.com (WWWgraphix) wrote:
> >I wasn't going to respond to this article at first, as I figured that
> >there were more than enough people on this newsgroup that were more
> >qualified to answer that I am. I'm just an undergrad Earth and
> >Atmospheric Sciences major, so cut me a little slack if I mess this stuff
> >up. Here goes-->
> >
> >Clouds form when a parcel of air is lifted to a higher altitude and the
> >water vapor in the air is cooled to the point where it condenses and
> >coalesces, forming a cloud. After the water condenses, the parcel of air
> >cools at a different rate that normal (Wet adiabatic rate as opposed to
> >dry adiabatic rate). When air is defined as unstable, the parcel of air
> >cools slower than the surrounding air, and at a certain point can begin
> >rising under its own power, creating clouds with vertical development.
> >Cumuls clouds are an example of this. If the rising and expanding
> >continue, a Cumulonimbus cloud can form (big, towering cloud with anvil
> >head). So, actually, Clouds do float, contrary to what some guy said. I
> >think. Hope this helps.
Justin ... I think this answer goes a long ways beyond what the original
poster may have wanted. Your explanation is more or less o.k., but I
think it misses the mark. Parcel instability theory is a reasonable
meteorological answer, but it is probably a load of incomprehensible
jargon to someone asking why clouds float.
> Having stepped into the middle of a thread, I may be placing my foot
> firmly in mouth, but here goes anyway. The original question was Why
> do clouds float? The answer, simplistic as it may sound is this:
> Clouds are a visible manifestation of a parcel of air that is
> saturated with water vapor. Moist air is less dense than dry air.
> Clouds float, therefore, because they are less dense than the dry air
> below them. They don't rise above a certain level because at some
> point the air above the cloud is less dense than the air within the
> cloud. Clouds which are forced aloft due to strong thermal forces are
> the exception to this GENERAL, and SIMPLISTIC rule...
Ray ... this "explanation" pushed me over the edge into responding to this
thread. A parcel of moist air (only water vapor ... nothing CONDENSED) at
some given temperature is indeed less dense than a parcel of absolutely
dry air at the same temperature (when the volumes are the same), but this
"explanation" is NOT relevant to the issue of why clouds seem to "float."
The CONDENSATION of moisture releases heat, which is the dominant factor
making parcels of air less dense than their surroundings ... it's just
buoyancy. It is the ascent of air that eventually cools the parcel to the
the point where condenation begins (called the saturation point). When
the vapor condenses into droplets or ice crystals, these particles are
considerably more dense than air and so they fall. Since cloud particles
are very small, however, the fall velocity of cloud particles is small ...
they descend RELATIVE to the air in which they are found. In clouds,
typically, the air is rising ... so that the very small fall speeds of
cloud particles can be offset by the upward motion of the air within the
cloud. Ever watch time lapse movies of clouds? I think this motion of
the cloud particles is very evident in such movies.
Chuck Doswell
---------------------------------------------------------------------
Dr. Charles A. Doswell III NOAA/National Severe Storms Laboratory
1313 Halley Circle, Norman, Oklahoma 73069
phone: (405) 366-0439 fax: (405) 366-0472 <dos...@nssl.uoknor.edu>
WWW home page: <http://www.nssl.uoknor.edu/~doswell>
Standard disclaimer ... my views are my own; don't blame my employer.
In politics, we put aside emotion;
We deal with facts. ...Hassan Abdul-Rakhman
---------------------------------------------------------------------
EBurger
>considerably more dense than air and so they fall. Since cloud particles
>are very small, however, the fall velocity of cloud particles is small
...
>they descend RELATIVE to the air in which they are found. In clouds,
>typically, the air is rising ... so that the very small fall speeds of
>cloud particles can be offset by the upward motion of the air within the
>cloud. Ever watch time lapse movies of clouds? I think this motion of
>the cloud particles is very evident in such movies.
> Chuck Doswell
Also, one might think of the cloud as a form (like a waterfall), rather
than an object (like a pool of water). That is, even if the small and
hence slowly falling (because the small size makes a large
surface-area-to-volume ratio and air resistance force can equal weight at
very low falling speeds) cloud droplets do fall, they may consistenly
evaporate upon reaching the cloud base, only to be replaced by new ones
forming at the top of the cloud - hence the waterfall analogy.
I'm sure Dr. Doswell's answer is more to the point, since the air is in
fact rising (maybe the droplets actually form at the bottom and evaporate
when they reach the top?), but that 'form versus object' idea is perhaps
also a useful thing to keep in mind. Even if an identifiable cloud were
to last all day, it might well consist of different water droplets by
then. Right?
Tom Ehrensperger
Joseph Bartlo
I'll provide some numbers to consider :
Average cloud droplet size is 10 micrometers, most varying between
5 & 20 micrometers. These fall (undisturbed) at speeds of fractions
of a cm/sec (averaging about 6 mm/sec). That is about 22 m/hour.
Thus, if you watched such a cloud with a base of 1600 m for an
hour (if it existed that long), the 1-2 % change of its height might
be perceptible.
Drizzle drops are about 500 micrometers (diameters). They fall
quicker - about 1.8 m/sec. But they are no longer clouds then, but
precipitation. Typical raindrops of 3.5 mm diameter fall at speeds
of about 7 m/sec.
Those numbers might not be exactly right, but the idea is that
clouds can descend very slowly, but are affected much more
by local air currents, which tend to be upward to form them.
Most vertical velocities at clouds are much greater than fall
speeds of cloud droplets, sometimes drizzle drops, and
occasionally raindrops. Thus, rain often begins as between
updrafts, causing cold downdrafts to form. Often parts of a
cumulonimbus cloud (e.g. mamattus, cirrus anvils) will descend
quite rapidly. Quite often you might notice cumuliform clouds
descend before dissipating during evening, after thermals have
diminished.
All things considered, cloud base heights tend to be fairly
constant because rising air becomes saturated there, causing
a cloud to form. Small drops fall from a cloud base during
transition from cloud droplets to raindrops, often causing a
ragged appearance when they evaporate below cloud bases.
Often they cause cloud base to lower.
Joseph
Justin Reedy
In article <doswell-2112...@doswell.nssl.uoknor.edu>,
Chuck Doswell <dos...@nssl.uoknor.edu> wrote:
>
>Justin ... I think this answer goes a long ways beyond what the original
>poster may have wanted. Your explanation is more or less o.k., but I
>think it misses the mark. Parcel instability theory is a reasonable
>meteorological answer, but it is probably a load of incomprehensible
>jargon to someone asking why clouds float.
Thanks Chuck. You're probably right. My bad on that one.
>thread. A parcel of moist air (only water vapor ... nothing CONDENSED) at
>some given temperature is indeed less dense than a parcel of absolutely
>dry air at the same temperature (when the volumes are the same), but this
>"explanation" is NOT relevant to the issue of why clouds seem to "float."
>The CONDENSATION of moisture releases heat, which is the dominant factor
>making parcels of air less dense than their surroundings ... it's just
>buoyancy. It is the ascent of air that eventually cools the parcel to the
>the point where condenation begins (called the saturation point). When
I knew this. I was just too dumb to mention it. Thanks again, Chuck!
>the vapor condenses into droplets or ice crystals, these particles are
>considerably more dense than air and so they fall. Since cloud particles
>are very small, however, the fall velocity of cloud particles is small ...
>they descend RELATIVE to the air in which they are found. In clouds,
>typically, the air is rising ... so that the very small fall speeds of
>cloud particles can be offset by the upward motion of the air within the
>cloud. Ever watch time lapse movies of clouds? I think this motion of
>the cloud particles is very evident in such movies.
[B
This part I didn't know. Somebody posted something very simplistic that
said the same thing but I didn't pay attention.
Again, I thank you for your corrections. I'm an aspiring (possibly) earth
and atmospheric science student at Ga Tech and I'm still learning this
stuff. See ya in a few years down at the NSSL. :)
>
> Chuck Doswell
Justin Reedy
Chuck Doswell
In article <19961222141...@ladder01.news.aol.com>,
ebu...@aol.com (EBurger) wrote:
> Also, one might think of the cloud as a form (like a waterfall), rather
> than an object (like a pool of water). That is, even if the small and
> hence slowly falling (because the small size makes a large
> surface-area-to-volume ratio and air resistance force can equal weight at
> very low falling speeds) cloud droplets do fall, they may consistenly
> evaporate upon reaching the cloud base, only to be replaced by new ones
> forming at the top of the cloud - hence the waterfall analogy.
I think this analogy might be a bit strained. I have my doubts that most
droplets would simply fall to cloud base. As Joseph Bartlo's numbers
suggest, a pretty modest upward motion would make them ascend relative to
the surface even if they are falling relative to the air. A waterfall is
simply descending water.
> I'm sure Dr. Doswell's answer is more to the point, since the air is in
> fact rising (maybe the droplets actually form at the bottom and evaporate
> when they reach the top?), but that 'form versus object' idea is perhaps
> also a useful thing to keep in mind. Even if an identifiable cloud were
> to last all day, it might well consist of different water droplets by
> then. Right?
This is an excellent point and one I should have mentioned, since I harp
on this topic a lot. A cloud is not a "thing" (although the droplets that
make it visible are!) in the sense that it is made up of the same
particles from minute to minute ... rather it is a "process" (my terms for
'form vs. object'). There are some terrific time lapse movies of
lenticular mountain wave clouds that illustrate the passage of air (and
droplets) THROUGH the cloud, but the cloud stays put. Thus, I believe
that Evan Gillespie's point is well-taken ... Clouds do not really "float"
like objects bobbing on the surface of the water ... nor are they like a
neutrally-buoyant jellyfish suspended at some depth in the water ...
rather, they are PROCESSES made visible by condensed water.
Justin Reedy
In article <doswell-2312...@doswell.nssl.uoknor.edu>,
Chuck Doswell <dos...@nssl.uoknor.edu> wrote:
(some clipped)
>
>This is an excellent point and one I should have mentioned, since I harp
>on this topic a lot. A cloud is not a "thing" (although the droplets that
>make it visible are!) in the sense that it is made up of the same
>particles from minute to minute ... rather it is a "process" (my terms for
>'form vs. object'). There are some terrific time lapse movies of
>lenticular mountain wave clouds that illustrate the passage of air (and
>droplets) THROUGH the cloud, but the cloud stays put. Thus, I believe
>that Evan Gillespie's point is well-taken ... Clouds do not really "float"
>like objects bobbing on the surface of the water ... nor are they like a
>neutrally-buoyant jellyfish suspended at some depth in the water ...
>rather, they are PROCESSES made visible by condensed water.
>
> Chuck Doswell
The whole "cloud is a process and not a thing" thing was very interesting.
I've never really heard anyone say that before. Of course, I haven't
heard an awful lot about clouds. Thanks again, Dr. Doswell, for your
insightful meteorological knowledge. Wow.
Justin "I wish I knew as much as you guys do" Reedy
Undergrad Earth and Atmospheric Science major
TMolina
I love such a question, beacause those "so easy" ones are the most
difficult to answer.
This is nothing a cloud.
Clouds do not flotate, they stay.
A cloud is a acumulation of droplets that are continiously
condensating from water vapour and evaporating again.
When you see a cloud from the ground, you see bilions of droplets that
are opaques to the light.
If you are flying, you enter the fog, and almost feel de humidity.
The same thing as the smell of the hot tea, or the vapour at the
bathroom.
What a thing if clouds flotate, we will be able to suspend on them and
stay like angels.
Sincerely.
Tomàs Molina
Barcelona
On 16 Dec 1996 23:44:02 GMT, wwwgr...@aol.com (WWWgraphix) wrote:
>Do clouds float due to some sort of "kite" effect? Or??
>TIA
>Dennis Spector
>wwwgr...@aol.com
Joseph Bartlo
Justin Reedy <gt3...@prism.gatech.edu> wrote in article
<5a139b$p...@acmey.gatech.edu>...
> The whole "cloud is a process and not a thing" thing was very interesting.
> I've never really heard anyone say that before. Of course, I haven't
> heard an awful lot about clouds. Thanks again, Dr. Doswell, for your
> insightful meteorological knowledge. Wow.
Lance Bosart said that to me many years ago regarding
cyclones, for which I think the statement is much more
applicable. At least clouds have visible boundaries;
though many processes cause them to change, often
quite rapidly.
Joseph
BM223
The troposphere is an ocean of watervapor and therefore clouds do float on
the
vertical lift of rising air saturated with watervapor. It rises to a
height of condensation and appears to stay there. As long as there is lift
there will be a
cloud.
MarkBM223
BM223
The troposhere is an ocean of watervapor and if it is forced up high
enough the
cooler air above will condense it giving the appearance of a large massive
object looming overhead. Scary isn't it?
MarkBM223