“ What Causes Our Weather”

I. Factors that cause weather :

A. Weather-Is the present state of our atmosphere.B. What causes our weather?

1. The interaction between the earth’s air, water, land and the sun causes the changes in our weather.C. There are 4 factors that determine

the type of weather we will receive:

1. Temperature

2. Air Pressure

3. Wind

4. Amount of moisture in the air. (Humidity!)

II. Heat Transfer on Earth :

A. The way the earth is heated controls the characteristics of the atmosphere.

B. Heat moves through earth in three different ways:1. Radiation

2. Conduction

3. Convection

C. Radiation-Energy that comes off of the sun and is absorbed by the earth.

1. When a surface on earth comes into contact with this radiation it either absorbs it or deflects it away. 2. If it absorbs it the surface will change it into heat.

D. Conduction-The transfer of heat when molecules collide into each other. 1. Molecules in hot objects move toward

the molecules in cold objects.

2. Heat is transferred to the colder object until the molecules are all the same temperature. 3. Ex. Frying pan on a stove.

E. Convection-The transfer of heat through convection currents. (Only through a fluid) 1. Hot molecules are less dense than

cold molecules. 2. A hot fluid will rise and a cold fluid will sink. 3. This causes convection currents. 4. Ex. Water boiling on a stove.

III. Air Pressure:

A. Air Pressure-The weight of the atmosphere as it pushes down on earth’s surface. B. Three factors determine air pressure:

1. Temperature of the air.

A.) The higher the temperature, the lower the air pressure.

2. Density of the air. (Elevation) A.) The higher the density, the higher the pressure.

3. The amount of water vapor. (Humidity) A.) The higher the humidity, the

lower the pressure.

IV: Wind:

A. Why do we get different wind systems?1. Uneven heating of the earth causes

different air temperatures.

2. That can change the air pressure.

3. Wind blows from areas of high pressure to areas of low pressure.

B. Coriolis Effect:

1. This also will affect wind systems.

2. Coriolis Effect- Is the result of the earth’s eastward rotation.

3. It pushes winds in the northern hemisphere to the right (clockwise), and to the left (counter clockwise) in the southern hemisphere.

C. The Different Wind Systems:

1. Winds are named for the direction they blow from. 2. There are four global wind zones on earth. A.) Doldrums-Windless zone of the

earth that is located in the 0 to 5 degree latitudes. B.) Trade Winds-Blow from east to west

and are located between 5 to 30 degrees North or South latitude.

“Northeast or Southeast

Trade Winds”

C.) Prevailing Westerlies-Blow from west to east located between 30 to 60 degrees north or south latitude.

Responsible for our weather.

D.) Polar Easterlies-Blow from east to west and are located between 60 to 90 degrees north or south latitude.

D. Minor or Local Wind Systems:

1. Earth also has some local wind systems that affect our weather. 2. Jet Stream- Narrow belts of strong

winds in the upper troposphere.

A.) There are two jet streams in each hemisphere.B.) They can change position daily.

C.) When they do they have a major influence on weather.

3. Sea Breeze- Cold winds blowing from the water to the land.

A.) It is a convection current of wind caused by the land warming faster during the day than the water does.

4. Land Breeze- Cold winds blowing from the land to the water.

A.) It is a convection current of wind caused by the land cooling faster at night than water does.

E. Monsoon Winds:

2. There are two types of Monsoon winds: A.) Summer Monsoon- Large sea

breezes that bring a season of heavy rain.

1. Monsoon winds- Sea or land breezes that cover a large area and change direction with the seasons.

B.) Winter Monsoon- Large land breezes that bring a season of very dry weather. C.) Common Monsoon locations are South East Asia (India), West Africa, and North Eastern South America.

V. The amount of Moisture in the Air:

A. Water Cycle-Continuous movement of water between the atmosphere and the surface.

1. Water starts off in oceans, lakes, rivers, glaciers, etc.

2. It then evaporates.

A.) Evaporation-The process of liquids turning to gas.

3. Then the gas condenses.

B.) Condensation-The process of a gas turning into a liquid.

4. When clouds of water become to heavy, the water precipitates back to earth. A.) Precipitation-Water drops that fall

from the clouds because the clouds could no longer support them.

5. Precipitation then replaces water that has already evaporated.

A.) Ground Water & -Runoff

Replaces the water that has evaporated.

B. Humidity-The amount of water in the air. 1. Why can air hold water?

A.) Air acts like a sponge. B.) Holes in the sponge allow it to hold water.C.) Air holds water in a similar way.

D.) Water fits into the spaces between the molecules of air. E.) When the air can’t hold any more water clouds start to form.

C. Relative Humidity- Compares the actual amount of water vapor in the air with the maximum amount of water vapor the air can hold. 1. Relative humidity is expressed as a

%. 2. If the relative humidity is 100 % the air can not hold any more water. 3. Saturation- When air contains as much

moisture as possible. . 4. Additional water added to the air will condense back to a liquid, depending on the temperature.

5. Dew Point- The temperature at which air is saturated and water vapor in the air condenses.

D. Two things determine relative humidity: 1. Temperature of the air.

A.) Warm air can hold more moisture than cold air.

2. The amount of moisture added or subtracted into an area.

A.) ex. Bathroom after a shower.

3. When will relative humidity be the highest?

A.) Cold temperatures.

B.) High Water levels in the air.