Weather: A study in variables

Pressure

Variable Review: Atmosphere - Structure

Consists of four major layers (top to bottom) Thermosphere Mesosphere Stratosphere Troposphere - where we live & weather happens Mnemonic: Too Many Stupid Tests

As you move upward from the surface, Pressure decreases in each layer Temperature “zig zags” ( as you go up)

Heat transfer in atmosphere

Only 3 options: Conduction Convection Radiation

Heat flow is ALWAYS from high energy to low energy

Heat energy measured with temperature

Temperature affects air pressure

Changing variables has effects!

Pressure

Air pressure(book definition): the amount of force per unit area exerted by air. Caused by gravity. A measure of the force/weight of moving air

molecules. Measured with a barometer.

Milimeters of mercury (mmHg) Milibars (mb)

One atmosphere at sea level = 14.7 psi

How does 14.7 psi feel?

Two Volunteers?

(must be prepared to summarize experience/observations)

Pressure Gravity affects air pressure:

Keeps the atmosphere here! It causes air pressure! (Smaller planets/moons don’t have atmospheres due to LACK of gravity.)

Altitude affects air pressure: Air pressure is affected by depth. The deeper we

are in air, the more pressure there is. Higher altitudes are like being in the “shallow

end”.

Pressure

The deeper we are in a fluid, the more pressure there is!

There are more molecules on top of you!

Pressure: High/Low

High pressure = there are more molecules bumping into a surface. There are more molecules stacked on top of an area.

Low pressure = There are less molecules bumping into a surface. There are less molecules stacked on top of an area.

How does temperature and water affect air pressure?

Temperature Hypothesis: If temperature increases, then air pressure will _______________.

Water Hypothesis: If water increases, then air pressure will ____________________.

The effects of Water Vapor & Temperature

Temperature: Higher temperature means less pressure.

Air is less dense and molecules are more spread out.

Lower temperature means more pressure. Air is more dense and molecules are more compact.

Water vapor: The more water vapor, the less pressure. The less water vapor, the more pressure. Water molecules weigh less(MW) than some gases.

Pressure and Temperature

Hot fluids rise, cold fluids sink. We know that! (helps explain convection)

Warm temperatures mean molecules spread out. Molecules are moving more. (fast dance tempo)

Lowers the density. Less dense means it rises. Rising molecules means less of them bumping or stacking

on the surface of the earth. Warmer temperatures mean lower pressure. Colder temperature = molecules huddling together(moving

less) = high pressure. (slow dance tempo)

Wait a minute. . .

If warm air means less pressure, then why do we get colder rainy days with a low pressure system? And. . .

Why does a high pressure system seem to go with clear warm days?

We will discuss these answers as we add more variables!

Pressure and Wind

Nature abhors a vacuum! Wind is a result of differences in air pressure.

Air will always move from areas of high pressure to areas of low pressure.(isobar map activity)

Isobars: lines connecting weather stations with equal pressure

Wind blows perpendicular to isobars. The closer the isobars, the larger the pressure difference

or pressure gradient. The steeper the pressure gradient, the stronger/faster

the winds in that area.

What causes differences in pressure?

Because the earth is heated unevenly, there will always be pressure differences.

So, as long as the sun will shine, the wind will blow.

Where on Earth, in general, is it the hottest? Where on Earth, in general, is it the

coldest?

Global Pressure Patterns

Lowest Pressure

Highest Pressure

Highest Pressure

Global Wind Patterns