Students will be able to identify three properties of the atmosphere and how they interact.

Students will be able to explain why atmospheric properties change with changes in altitude.

Density: The mass per unit volume of a material.

Exert: To put forth.

P. 289 Main

Idea

Atmospheric properties, such as temperature, air pressure and humidity describe atmospheric conditions.

• P. 289 • Temperature: A measure of movement. The faster the particles of a substance move, the higher is their temperature.

• 3 Scales of Measurement:1. Fahrenheit (˚F) (Most common in

US)2. Celsius (˚C)

• These are based on the boiling and freezing points of water.

3. Kelvin (˚K)• Based on Absolute Zero – where all

movement of particles stops.

Air temperature changes with changes in altitude.

P. 290 Air pressure: The weight of air exerted on a surface.• Units: N / m² or millibars (mb.)

100 N / m² = 1 mb. At sea-level atmosphere exerts pressure

of 1000 mb. As you go higher in the atmosphere the

air pressure decreases.

Air pressure decreases with altitude (height.)

P. 290 Density of Air: As you get higher in the atmosphere, density decreases because air molecules are more spread out.

As with air pressure, as you get higher into the atmosphere, the density of air also decreases.

P. 291 Pressure – Temperature – Density Relationship:• Air pressure and Temperature:

For air with the same density, warm air is at a higher pressure than cool air.

• Air pressure and Density: For air with the same temperature high

density air is at higher pressure than low density air.

• Temperature and Density: At the same pressure, warmer air is less

dense than is cooler air.

P. 291

P. 292

Temperature Inversion: When warm air is on top of cooler air (occurs in troposphere.)• Causes: Cold clear nights, Earth

does not radiate heat to lower levels of atmosphere.

• Effects: Fog, low lying clouds and smog – smoke and fog (Haze).

• We normally expect air to become colder as we increase in altitude in the troposphere.

Cold air is normally above warm air.

9.293 Wind: Warm air is less dense than cool air.• Air moves from more dense areas to

less dense areas (WIND.)• Differences in air densities caused

by differences in heating Earth’s of surface.

Warm air is less dense than cool air because air molecules are more spread out.

9.293 Wind and Pressure Differences:• In atmosphere air pressure

increases as density increases.• Result:

Air moves from regions of high pressure (COLD - DENSE) to regions of low pressure (WARM – LESS DENSE.)

9.293 Wind Speed and Altitude:• Earth’s surface creates friction with

wind (slows it down.)• Higher in the atmosphere wind

blows faster.

In the Troposphere wind speed increases with altitude.

9.294 Humidity: The amount of water vapor in a given location of the atmosphere.• Expressed as relative humidity and

dew point.• Saturation: when the amount of

water vapor in the air has reached its maximum point. (The air can’t hold anymore.)

SaturatedNon saturated

9.294 Relative Humidity: Amount of water vapor in air relative to amount of vapor needed for air to reach saturation (expressed as a percent.)• Example: Forecast says relative

humidity = 50% Means the air is holding half of the vapor

it is capable of holding.

Relative humidity is expressed as a percent.

9.294 Dew Point: Temperature at which air reaches saturation – when it will rain.• Cooler air has lower dew point.• Why we have high humidity in the

summer.