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PROF JOHN GYAKUM: If we look at a plane section, or looking down

upon a supercell thunderstorm, with the axis up and down actually being

north-south, and the axis horizontal being east-west,

we can see the overall structure of the precipitation seen here.

And that represents a combination of factors.

In the outermost area we see relatively light rain forming,

but as we go in towards the center of this supercell thunderstorm, the rain

itself increases in intensity to the extent

that we might actually have very, very significant hail forming in the middle.

And then what we actually see oftentimes is the sense

of rotation in the vicinity of the supercell thunderstorm.

That rotation itself is actually oftentimes

a very good location for the production of a tornado.

Now the rear flank, this RFD, which is what we call a rear flight down draft,

is an area in which the cloud mass is effectively ultimately sinking

in association with evaporative cooling.

In the very center here we have the heaviest of rain,

and in some cases hail.

And this rotation that we see here that is associated

with this little area of rotation in the supercell thunderstorm itself,

represents an ideal location for where the tornado might actually be forming.

So this zone of large scale rotation is oftentimes

the zone that is picked up by the Doppler radar

and represents the potential for a tornado to be touching down.

So if we look more carefully at a vertical section of a supercell

we can get an idea of what is happening on the basis of different scales.

And what we see here is this rotating wall cloud

manifested by a circulation that is somewhat smaller than what

we see in the supercell rotation itself.

And then actually somewhat bigger than what we see manifested in the tornado

represents an important potential for the development of a tornado.

Now what happens here is in the context of observing

what we might compute in terms of wind speeds.

The development of a tornado itself is based

upon what we call the concept of conservation of angular momentum.

So if we assume that the radius of our wall cloud that we're

looking at here in this picture is about one kilometer or 1,000 meters,

we can follow on with that by assuming that the rotation speed of this wall

cloud is about 10 meters per second.

So what that means is that the angular momentum, the momentum of this wall

cloud is 10 times 1,000, or 10,000.

Now if we assume that the tornado itself is a smaller radius, which is typically

the case on the order of 100 meters or a tenth of a kilometer, what we wound up

computing therefore, because of the conservation of angular momentum,

is that we get a wind speed of 100 meters per second.

And in fact the conservation of angular momentum

says that the radius of the wall cloud being, in this case

one kilometer times the wind speed, which gives us

10 meters per second times 1,000, or 10,000.

The left side is 10,000, the right side must also be 10,000.

And given that the radius of the tornado is only 100 meters, that means in order

to get 10,000 we divide 10,000 by 100 to get 100,

and that being the wind speed of the tornado, 100 meters per second.

So 100 meters per second times 100 meters

gives us 10,000 meters squared per second.

And clearly the wind speed in our tornado,

100 meters per second, that's on the order of 200 knots, which

is an incredible wind speed, much bigger than that associated

with a speed associated with the wall cloud.

upon a supercell thunderstorm, with the axis up and down actually being

north-south, and the axis horizontal being east-west,

we can see the overall structure of the precipitation seen here.

And that represents a combination of factors.

In the outermost area we see relatively light rain forming,

but as we go in towards the center of this supercell thunderstorm, the rain

itself increases in intensity to the extent

that we might actually have very, very significant hail forming in the middle.

And then what we actually see oftentimes is the sense

of rotation in the vicinity of the supercell thunderstorm.

That rotation itself is actually oftentimes

a very good location for the production of a tornado.

Now the rear flank, this RFD, which is what we call a rear flight down draft,

is an area in which the cloud mass is effectively ultimately sinking

in association with evaporative cooling.

In the very center here we have the heaviest of rain,

and in some cases hail.

And this rotation that we see here that is associated

with this little area of rotation in the supercell thunderstorm itself,

represents an ideal location for where the tornado might actually be forming.

So this zone of large scale rotation is oftentimes

the zone that is picked up by the Doppler radar

and represents the potential for a tornado to be touching down.

So if we look more carefully at a vertical section of a supercell

we can get an idea of what is happening on the basis of different scales.

And what we see here is this rotating wall cloud

manifested by a circulation that is somewhat smaller than what

we see in the supercell rotation itself.

And then actually somewhat bigger than what we see manifested in the tornado

represents an important potential for the development of a tornado.

Now what happens here is in the context of observing

what we might compute in terms of wind speeds.

The development of a tornado itself is based

upon what we call the concept of conservation of angular momentum.

So if we assume that the radius of our wall cloud that we're

looking at here in this picture is about one kilometer or 1,000 meters,

we can follow on with that by assuming that the rotation speed of this wall

cloud is about 10 meters per second.

So what that means is that the angular momentum, the momentum of this wall

cloud is 10 times 1,000, or 10,000.

Now if we assume that the tornado itself is a smaller radius, which is typically

the case on the order of 100 meters or a tenth of a kilometer, what we wound up

computing therefore, because of the conservation of angular momentum,

is that we get a wind speed of 100 meters per second.

And in fact the conservation of angular momentum

says that the radius of the wall cloud being, in this case

one kilometer times the wind speed, which gives us

10 meters per second times 1,000, or 10,000.

The left side is 10,000, the right side must also be 10,000.

And given that the radius of the tornado is only 100 meters, that means in order

to get 10,000 we divide 10,000 by 100 to get 100,

and that being the wind speed of the tornado, 100 meters per second.

So 100 meters per second times 100 meters

gives us 10,000 meters squared per second.

And clearly the wind speed in our tornado,

100 meters per second, that's on the order of 200 knots, which

is an incredible wind speed, much bigger than that associated

with a speed associated with the wall cloud.

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