Know basic facts and general principles of the atmosphere.1. Define a list of terms related to the

atmosphere.2. Describe the roles of water in the

atmosphere.

The Atmosphere

Overview1. Describing the Atmosphere.2. Roles of Water and the Atmosphere.

Atmospheric ElementsThe whole mass of air surrounding the Earth.Made up of a mixture of gases:

• 78% Nitrogen (N2)• 21% Oxygen (O2)• 1% Mixture of other gases

Atmospheric ElementsAbsorbs energy from the Sun, recycles water and

other chemicals, and works with the electrical and magnetic forces to provide a moderate temperature.

Protects us from high-energy radiation and the frigid vacuum of space.

Four distinct layers have been identified.

Atmospheric Layers

Troposphere

Starts at Earth’s surface and extends 10 to 13 kilometers.

Lowest, densest part of Earth’s atmosphere in which most weather changes occur.

Stratosphere

Starts just above the troposphere and extends to 50 kilometers.

Very dry and less dense compared to troposphere.

The ozone layer is located within the stratosphere.

MesosphereStarts above the stratosphere

and extends to 85 kilometers above the Earth’s surface.

Temperatures as low as -90o C.

Thermosphere

Starts just above the mesosphere and extends to 600 kilometers high.

Temperatures reach up to 1,727o C.

Known as the upper atmosphere.

Atmospheric PressureThe downward pressure

exerted by the weight of the overlying atmosphere.

Greatest at sea level and decreases outward from the Earth.

Plays a significant role in the type of weather that occurs.

THE BOOK TEST

Atmospheric Pressure

By watching atmospheric pressure changes at a location, forecasters can obtain clues to the expected changes in other weather elements.

Atmospheric Pressure

Low pressure regions usually experience more stormy weather with more cloudiness, higher humidity, and unstable conditions. (LOW = Lousy Weather)

High pressure regions are more likely to be associated with fewer clouds, lower humidity, and more stable conditions. (HIGH = Good Weather)

Winds blow because of the differences in air pressure on and above the Earth’s surface.

Atmospheric Pressure and Wind• Air flows from areas of high pressure into those of low pressure producing a clockwise circulation around an area of high pressure. The opposite is true of low-pressure areas; the air flows toward an area of low pressure and is deflected to create a counter-clockwise or cyclonic circulation.

Atmospheric Pressure and Wind

Water in the AtmosphereIn the troposphere, water goes through a cycle

from vapor to condensation to precipitation. As it goes through this cycle, it takes on several forms.

• Liquid

• Solid

• Condensation

Evaporation

The process by which liquid water molecules change to a gas or vapor state and enter the Earth’s atmosphere.

Temperature and pressure are the primary cause of water vapor in the air changing into clouds or falling to Earth.

HumidityAbsolute Humidity

• The actual amount of water vapor in the air at a given time.• The amount of water vapor the air is able to hold depends on

the temperature.

Humidity

Relative Humidity

• The amount of water vapor that can still enter the air mass before it becomes saturated.

• Expressed by a percentage figure which is the ratio of the amount of water vapor in the air to the maximum amount that the same volume of air could contain at a given temperature and pressure.

• Saturation Point = DEW POINT

Condensation and Precipitation When part of the water vapor in the air

returns to a liquid or solid form, it is seen as either condensation and/or precipitation.

Dew Point TemperatureThe temperature at or below which water vapor

will condense is the key factor in condensation and precipitation.

SummaryLevels of the AtmosphereAtmospheric PressureWater in the AtmosphereHumidityCondensation and Precipitation