Perspicuo
Veteran Member
I've always wondered if you could tell if the wind is blowing fast or slow up high by looking at the clouds the wind pushes, I mean they're shape or type.
-
Features
Can you tell the speed of the wind by...
- Thread starter Perspicuo
- Start date
Malintent
Veteran Member
Yes. Sort of. There are many layers of clouds and wind. The wind at the surface is (almost) always slower than the winds aloft. There may be dozens of layers of wind, in all 360 degrees of direction. "wind sheer" is the term describing a sudden change in wind direction, either within a layer, or between layers.
Don't think of the clouds as being "pushed by the wind". Masses of air (measured in cubic miles, for example) move at a speed and direction governed by pressure gradients at different locations. Clouds are part of that air mass. "Wind" is the phenomena of an air mass moving past a stationary object. So, clouds do not "move"... the air mass that contains the cloud moves.
That said, this applies to most fluffy cumulous clouds that most people experience day to day. There are all kinds of clouds that form due to interactions with other phenomina... lenticular clouds, for example, only form over mountains due to mechanical turbulence of any air mass passing over it. Those clouds are fairly stationary, as it is the rapid change in altitude the air mass is forced to take over the mountain that causes it to form.
Don't think of the clouds as being "pushed by the wind". Masses of air (measured in cubic miles, for example) move at a speed and direction governed by pressure gradients at different locations. Clouds are part of that air mass. "Wind" is the phenomena of an air mass moving past a stationary object. So, clouds do not "move"... the air mass that contains the cloud moves.
That said, this applies to most fluffy cumulous clouds that most people experience day to day. There are all kinds of clouds that form due to interactions with other phenomina... lenticular clouds, for example, only form over mountains due to mechanical turbulence of any air mass passing over it. Those clouds are fairly stationary, as it is the rapid change in altitude the air mass is forced to take over the mountain that causes it to form.
Shadowy Man
Contributor
Having lived in Colorado for a few years, I can tell you that there were definitely certain cloud patterns that were associated with high winds in the mountains. I could look up and know that it was windy up there.
bilby
Fair dinkum thinkum
- Joined
- Mar 6, 2007
- Messages
- 35,761
- Gender
- He/Him
- Basic Beliefs
- Strong Atheist
A 'cloud' is not really an object in its own right; it is a characteristic of the atmosphere at a given point.
The lenticular clouds Malintent mentions above are a very good example of this; Air flowing over a mountain may be moving at high speed, but the cloud appears not to move. The entire airstream in which the cloud exists is moving at a fairly uniform speed; the cloud is the portion of that airstream where the temperature and humidity conditions are such that the air becomes opaque. Air flowing towards the mountain transitions to opacity as water or ice crystals form; and air flowing away from the mountain transitions back to transparency as the water or ice crystals re-evaporate. The air moves at high speed relative to the ground; but the transition zones do not move much at all.
The 'edges' of a cloud are transition zones; these transition zones can move with the airflow, or they can move independently of it.
Radar or ultra-sonic techniques are therefore far superior for measuring wind speeds at altitude than observing cloud movement, as the radar detects the way the individual water droplets in the cloud are moving, rather than the less reliable motion of the transition zone that forms the visible cloud boundary.
The lenticular clouds Malintent mentions above are a very good example of this; Air flowing over a mountain may be moving at high speed, but the cloud appears not to move. The entire airstream in which the cloud exists is moving at a fairly uniform speed; the cloud is the portion of that airstream where the temperature and humidity conditions are such that the air becomes opaque. Air flowing towards the mountain transitions to opacity as water or ice crystals form; and air flowing away from the mountain transitions back to transparency as the water or ice crystals re-evaporate. The air moves at high speed relative to the ground; but the transition zones do not move much at all.
The 'edges' of a cloud are transition zones; these transition zones can move with the airflow, or they can move independently of it.
Radar or ultra-sonic techniques are therefore far superior for measuring wind speeds at altitude than observing cloud movement, as the radar detects the way the individual water droplets in the cloud are moving, rather than the less reliable motion of the transition zone that forms the visible cloud boundary.
Perspicuo
Veteran Member
So the answer is 'no', then?
Malintent
Veteran Member
My answer is, "It depends on the type of cloud you are observing".
relatively small, fluffy, roundish clouds (like cotton balls) are most reliably moving along at the same speed and direction as the winds aloft at their altitude. However, this speaks in no way to the surface wind speed or direction underneath the cloud.
At the time I post this, the atmosphere around JFK airport is moving as follows:
From 0 - 3000 feet: 120 degrees at 11 knots
From 3001 - 6000 feet: 0 degrees at 0 knots
From 6001 - 9000 feet: 290 degrees at 8 knots
...
From 39000 feet - 42000 feet: 250 degrees at 27 knots
relatively small, fluffy, roundish clouds (like cotton balls) are most reliably moving along at the same speed and direction as the winds aloft at their altitude. However, this speaks in no way to the surface wind speed or direction underneath the cloud.
At the time I post this, the atmosphere around JFK airport is moving as follows:
From 0 - 3000 feet: 120 degrees at 11 knots
From 3001 - 6000 feet: 0 degrees at 0 knots
From 6001 - 9000 feet: 290 degrees at 8 knots
...
From 39000 feet - 42000 feet: 250 degrees at 27 knots
Perspicuo
Veteran Member
I would think that more streamlined or "pulled apart"-looking clouds were in the midst of opposite winds at perhaps great speed.
Valjean
Veteran Member
- Joined
- Dec 26, 2009
- Messages
- 1,349
- Location
- Albuquerque, New Mexico, USA
- Basic Beliefs
- Vedanta. Many worlds physics, Environmentalism, Socialism.
My city's a favorite of hot air balloonists because we commonly get low altitude layers of wind moving in opposite directions, allowing a balloonist to float in one direction for a while then change altitudes to return to the take off site.
Perspicuo
Veteran Member
How can you tell where they are, senyorni?
skepticalbip
Contributor
- Joined
- Apr 21, 2004
- Messages
- 7,304
- Basic Beliefs
- Everything we know is wrong (to some degree)
The National Weather Service is a good source for wind speed and direction vs. altitude along with a lot of other useful meteorological information.
Witnessing (or participating in) the Alburqurque hot air balloon festival is something that should be on everyone's bucket list.
Malintent
Veteran Member
Google "winds aloft" for more information, but here is an excellent source of hourly data, across the US:
https://aviationweather.gov/products/nws/winds/
Each column is an altitude block (surface - 3000 ft., then 3001 - 6000 ft., etc..)
Each row is an airport identifier for where in the US the data was collected
Each value is a block of data in this format:
DDSS[+/-]TT
where DD = magnetic heading of wind to the nearest 10 degrees (i.e "24" = 240 degrees)
SS = speed of wind in knots
[+/-]TT = Temperature in degrees C. (all temps are assumed negative above 24k or so)
So, 3211+10 = winds at 11 knots heading 320 degrees (Northwest), temperature 10 degrees C.