8/1/11

Heat Waves

A Bermuda High is a

high-pressure air system

that starts, and stays,

along the East Coast.

Heat Waves

Think of the draft of air

created by a helicopter’s

propellers.

Heat Waves

A similar phenomenon

happens with the

swirling air of the high

pressure front.

Heat Waves

The downward force

comes, in part, from the

torque created by the

force of the wind (F) and

the radius (r) of the high-

pressure system.

Heat Waves

The direction of torque

is always

perpendicular to the

plane formed by the

radius and the force.

Heat Waves

You can think of the

high-pressure system

as a rotating cylinder

of humid air.

Heat Waves

Torque is a force and

this force is applied

over the column of air.

Since pressure is force

divided by area, then

the overall effect is to

increase the air

pressure.

Heat Waves

The downward pressure

pushes out cooler air,

and this persists during

the high-pressure

system. This causes a

temperature increase.

Heat Waves

The downward pressure

also keeps cooler air

fronts from breaking

through the high-

pressure system. This

keeps temperatures

warm.

Heat Waves

A continual flow of

warm, moist air from

the Caribbean keeps

the high-pressure

system intact. This

prolongs the heat.

Heat Waves

The warm, moist air

from Caribbean is

heavier than cool, dry

air. This causes an

increase in pressure

and temperature.

Heat Waves

But how much pressure

does the high-pressure

system add to the

regions affected by this

system?

Heat Waves

Pressure is the ratio of

the downward force

and the area of the

high-pressure system.

For a cylinder the

pressure formula

changes to this.

Heat Waves

As we saw earlier, the

downward force from

the pressure system is

the torque. Express

torque in force units.

Heat Waves

Torque is the product

of angular momentum

(I) and angular

acceleration (α). For a

rotating disk, the

torque formula is as

shown here.

Heat Waves

Use this formula for

torque in the pressure

equation.

Heat Waves

We cannot directly

measure the mass but

we can estimate mass

using the density of air

and volume of the

cylinder.

Heat Waves

Inputting the mass

equation into the

pressure equation and

simplifying yields a

fairly simple equation.

Heat Waves

This graph shows the

pressure as a function

of radius, with

parameters for h, α,

and ρ. The horizontal

graph shows standard

pressure.

Heat Waves

As the radius

increases, so does the

air pressure, and as a

result, so does the

temperature.