CLIMATE UNIT

I. Definitions

A. Weather--day by day variations in temperature (temp), winds,pressure and precipitation (ppt)

B. Climate--average seasonal weather for an area, usually described in terms of monthly averages of temp and ppt.

Before we can study about weather and climate we

need to know a little about Earth movements and Earth/Sun relations.

II. Earth Movements & Earth/Sun Relations

A. Rotation1. The earth rotates on its axis.

2. It takes 24 hours to make one complete rotation.

3. Therefore, when we look at rotation we can talk about day and night and time zones.

B. Revolution1. The earth revolves around the

sun.

2. It takes approx. 365 days to make one

complete revolution.

3. Therefore, when we look at revolutions of Earth around the

sun we can explain seasons.

See diagrams and handout.

North Pole

South Pole

Equator

Tropic of Cancer

Tropic of Capricorn

Circle of Illumination

Arctic Circle

Antarctic Circle

North Pole

South Pole

Equator

Tropic of Cancer

Tropic of Capricorn

Circle of Illumination

Arctic Circle

Antarctic Circle

North Pole

South Pole

Equator

Tropic of Cancer

Tropic of Capricorn

Arctic Circle

Antarctic Circle

Circle of Illumination

III. Climate ElementsA. Temperature

(temp.)--the amount of heat in the

atmosphere.

B. Precipitation (ppt)--the falling moisture

onto the earth, rain, snow, sleet, hail, fog, etc.

C. Air Pressure & Wind

1. Air Pressure--is the weight of the air (the air being forced

down or let up.)

2. Wind--horizontal movement of air.

*******************************The climate controls act upon the elements to produce

different climates. ******************************

IV. Climate Controls

A. Latitude

1. Low Latitudes or Tropics

a. Area between the Tropic of Cancer and Tropic of Capricorn (it actually extends a little north and south to 30N and 30S).

b. Tend to be warm to hot year round.

c. Where the sun’s rays are perpendicular

Low Latitudes

30 N

30 S

0

2. Middle Latitudes or Temperate Region

a. 30 to 60 North and 30 to 60 South

b. Neither hot nor cold--will get cold part of the year and hot part of the year.

c. Has seasons

Middle Latitudes

Low Latitudes

Middle Latitudes

60 N

30 N

30 S

60 S

0

3. High Latitudes or Polar Regions

a. 60 to 90 North and South

b. The sun is never directly overhead

and with the times of darkness it

gets very cold.

High Latitudes

Middle Latitudes

Low Latitudes

Middle Latitudes

High Latitudes

90 N

90 S

60 N

30 N

30 S

60 S

0

Cold all year

Cold all year

Seasons

Seasons

Hot all year

B. Continentality

1. In general, large land masses will have greater changes in temp.

2. Land will get hotter and colder depending on the temp. of the air.

3. Large bodies of water stay relatively the same temp. all year.

4. Therefore, if wind crosses over water to get to a place it will stay relatively the same temp. all year.

If it crosses over land there will be greater variations of temperature change.

C. Elevation

1. The higher up a mountain

you go--the cooler it gets.

2. For every 1000’ the temp.drops

3.6 F.

3. Therefore, in highland areas the temp. will vary depending on where you are on the mountain side.

A

B C

D

E

F

G

H

I

J

K

D. Atmospheric Circulation

1. General Facts

a. The Low Lat. receive

more heat.

b. Heat is transmitted to the higher lat. by

ocean currents & atmospheric circulation.

2. Pressure Systems

a. Because of uneven heating, areas of high and low pressures develop.

1) Low Pressure

a) Where the earth is relatively hot the atmosphere is heated causing the surface air to expand and rise.

b) i.e. Heated air rises--expands and is less dense--low pressure.

L

H

H

30 N

0

30 S

Hadley Cell

2) High Pressure a) As the air cools it becomes more dense.

b) Air begins to sink--High

Pressure

30 N

0

30 S

L

H

H

60 N

60 S

L

L

b. Air moves from a High Cell to a Low Cell along the surface of Earth.

c. As the air moves parallel

to Earth wind systems develop.

d. Because of Earth’s rotation the winds are deflected to the left in both the Northern Hem. & the Southern Hem.

Coreolis Effect

e. Therefore, air moving out of a High Cell in the Northern Hem. is clockwise & counterclockwise in the Southern Hem.

f. As the air moves into a Low Cell it is counterclockwise in the Northern Hem. & clockwise in the Southern Hem.

H

L

Northern Hemisphere

H

L

Southern Hemisphere

Northern Southern Hem. Hem.

High Cell CW CCW

Low Cell CCW CW

g. High Pressure Cells -- stable weather conditions, clear, dry (no ppt.)

h. Low Pressure--unstable, rainy, windy.

(hurricanes,typhoons, cyclones,tornadoes, willy willies, etc.)

3. Wind Belts a. Out of the High Cells we get winds as the air moves to a Low Cell.

b. In a Low cell the air is rising--

no wind.

c. In a High cell the air is

sinking-- no wind.

d. Winds are named from where they come. --See diagram.

Westerlies

Westerlies

NE Trades

SE Trades

0

30 S

60 S

30 N

60 N

Horse Latitudes

Horse Latitudes

Doldrums

4. Air Masses a. Independent of the wind systems, masses of air move into an area.

b. Each has its own temp. & ppt. characteristics.

1) Warm Masses, Cold Fronts, etc.

2) Marine vs. Continental Air Masses.

c. Fronts are places where a mass of warm air meets a mass of cold air.

When they meet--clouds and ppts. occur. Usually clear afterwards.

High Cell--DryDry

Low Cell--WetWet

E. Ocean Circulation 1. Ocean currents help move the heat from the equator to the

poles.

2. Ocean Currents are clockwise in the N. hemisphere and counterclockwise in the S. hemisphere.

3. Each current is considered a warm, hot, cool or cold current depending on where it is.

4. See Map.

4

1

33

12

65

7

8

11

910 12

13

14

15

16

5. In general,a. Warm currents: along the equator

b. Hot currents:

W side of ocean

E side of continents

c. Cool currents: near Arctic and Antarctic circles

d. Cold currents: E side of ocean

W side of continents

6. Moisture is not picked up from a cold current. It will be picked up from a hot current.

Hot Current--WetWet

Cold Current--DryDry

F. Mountain Barriers

1. Barriers will block the winds and funnel them in different areas

a. Rocky Mts. funnel the winds through the Great Plains and block south California

b. The Alps block cold air from the

north keeping N. Italy warm

c. The Himalayas keep India

warmd. etc.

2. Orographic ppt.

Warm, moist air

Dry air

Windward-- wetwet

Leeward-- drydry

Dew Point

a. Deserts can result on the

leeward side (Atacama Desert)

b. Rainy on the windward side (Washington & Oregon--windward of the Cascade Mts.)

1 2

3

5

4

6

7

8

9

10