1. Earth Science
Chapter 8
Climates

2. Climates
Climate - an average of weather conditions over a long-term period of time.
Driven by interaction of solar energy with Earth’s surface and atmosphere.
Based on conditions of temp. and humidity.
Determined by ratio of amount of moisture in the air to potential for evapotranspiration.

3. Water Cycle and Climates
Some latitude zones have a surplus of precipitation over evaporation or vice-versa.
Precipitation excess occurs at the equatorial and two middle latitude zones (40o to 70o).
Precipitation deficit occurs between 10o and 40o in each hemisphere.
A belt of convection currents moves the moisture from places of high humidity to places of low humidity.

4. Water Cycle and Climates

5. Water Cycle and Climates
A land and sea moisture exchange takes place because continents have more precipitation than evaporation.
Moisture from evaporated sea water is transported to continents by winds.
The water cycle is a closed system
Water that evaporates in one place usually precipitates hundreds to thousands of miles away.

6. Insolation and Earth’s Surface
Insolation (INcoming SOLar radiATION) is the major source of energy for Earth.
About half of the insolation received by Earth is short-wave radiation, which we see as light.
The rest is long-wave radiation (heat).
Most of the short-wave radiation absorbed by Earth is re-radiated from Earth’s surface as long-wave infrared energy.
Angle and duration of insolation influence climate

7. Factors Affecting Insolation
Angle of insolation
The angle at which the sun’s rays strike Earth.
Because Earth’s surface is curved, the Sun’s rays strike at angles from 0o to 90o.

8. Factors Affecting Insolation
Rays that strike Earth’s surface at a 90o angle are called direct.
As the angle of insolation decreases from 90o, the suns rays become less direct and more spread out over a larger area.
Direct rays provide the greatest intensity of insolation, because the insolation is spread over the smallest possible area.
Locations receiving direct rays will have higher temperatures.

9. Factors Affecting Insolation
At any location on Earth’s surface, the angle and intensity of insolation vary with time of day.
Greatest at solar noon
Lowest at sunrise and sunset

10. Factors Affecting Insolation
The intensity of insolation varies with the seasons of the year.
Seasonal changes are NOT related to the Earth’s varying distance from the sun.
Seasonal changes are caused by:
Tilt of Earth’s axis
Parallelism of Earth’s axis
Revolution around the sun

11. Factors Affecting Insolation

12. Factors Affecting Insolation
Because Earth is spherical every degree of latitude has a different angle of insolation.
As Earth orbits the sun direct rays are received from 23.5oN (summer solstice) and 23.5oS (winter solstice) due to Earth’s tilt.
At any given latitude the angle of the sun varies throughout the year.

13. Factors Affecting Insolation
Example for 43oN (Westmoreland):
On 3/21 & 9/23 the Sun is directly overhead at 0o.
On 3/21 & 9/23 the Sun’s altitude at 43oN is 47o.
On 12/22 the Sun is directly overhead at 23oS.
On 12/22 the Sun’s altitude at 43oN is 23.5o.
Lowest angle and intensity of year
On 6/21 the Sun is directly overhead at 23oN.
On 6/21 the Sun’s altitude at 43oN is 70.5o.
Highest angle and intensity of year

14. Factors Affecting Insolation

15. Factors Affecting Insolation
Duration of Insolation
The number of daylight hours at a given location.
Daylight hours vary with latitude and time of year
There is a direct correlation between the angle and intensity of insolation and duration.
When angle and intensity are greatest, duration is greatest.

16. Factors Affecting Insolation

17. Factors Affecting Insolation
The longer the duration of insulation, the higher the temperatures.
Earth is in radiative balance.
As the amount of insolation received by Earth increases, the amount of infrared energy radiated from Earth also usually increases.

18. Factors Affecting Insolation
Hottest time of day
Occurs some hours after solar noon
Insolation received is greatest at solar noon, but temp. continues to rise after solar noon because the incoming radiant energy exceeds the outgoing radiant energy.
Temp. rises until mid-afternoon when Earth is in radiatiave balance, then decrease until sunrise the next day when cycle starts again.
Coldest time of day?

19. Factors Affecting Insolation
Hottest time of year in Northern Hemisphere
Occurs in August
Insolation received is greatest at June 21, but temp. continues to rise for many days after June 21 because the incoming radiant energy exceeds the outgoing radiant energy.
Temp. rises until August when Earth is in radiatiave balance, then begins to decrease.
Coldest time of year?

20. Greenhouse Effect
Water vapor and carbon dioxide are present in the atmosphere
Let short-wave energy in from the Sun
Absorb long-wave infrared energy radiated from the Earth’s surface.
Results in raising of temperature in lower atmosphere.
Example:
Inside of car gets hot in the summer

21. Greenhouse Effect

22. The Water Budget
A monthly account of what happens to the water in an area over the course of a year is the water budget.
The “income” of a water budget is precipitation.
The “expenses” of a water budget is
potential evapotranspiration.
The amount of water that would evaporate if the water were available.

23. The Water Budget
The primary source of evapotranspiration is the Sun, so potential evapotranspiration is greatest in the summer and lowest in the winter.
If the total annual precipitation is less than the potential evapotranspiration the climate is arid.
If the total annual precipitation is greater than the potential evapotranspiration the climate is humid.

24. Factors Affecting Climate Patterns
The moisture and temperature conditions that affect a location depend on:
Latitude
Elevation
Proximity to large bodies of water
Ocean currents
Prevailing winds
Mountain ranges
Storm tracks

25. Factors Affecting Climate Patterns
Latitude
Most important factor affecting climate
At lower latitudes the temperatures remain fairly constant since the angle and duration of insolation remain fairly constant.
At higher latitudes, there is high variation in insolation resulting in high variation in temp.
As latitude increases, the average yearly temperature decreases, although the seasonal range of temperatures increases.

26. Factors Affecting Climate Patterns
Elevation
As elevation increases the temp. decreases and relative humidity increases.
At a given latitude places with higher elevation have more precipitation and a wider range of weather conditions than do places at lower elevation.
Changes in elevation have similar effects on temperature as changes in latitude.

27. Factors Affecting Climate Patterns
Large bodies of water
Water takes longer than land to absorb and radiate energy.
Temperatures at locations along the shore have a much smaller annual range than those at inland regions at the same latitude.
Areas regulated by water have a marine climate.
Inland areas with large temperature ranges have a continental climate.

28. Factors Affecting Climate Patterns
Ocean Currents
Warm ocean currents bring warm water from the equator to higher, colder latitudes, warming the air above them.
Cold ocean currents from the polar regions help cool the air over the southern regions.

29. Factors Affecting Climate Patterns
Prevailing winds
Air that originates over water may be carried over land, causing it to be very moist.
Air that originates over continental areas bring dry winds.
Low pressure belts (equator and 60o) consist of rising air which results in high humidity.
High pressure belts (30o and poles) produce dry conditions due to descending air.

30. Factors Affecting Climate Patterns
Mountains
The windward side of mountains are colder and have more precipitation than the warm, dry leeward side.
Storm tracks
Low pressure systems, which affect temperature and moisture, follow somewhat predictable paths.

31. Seasonal Wind Patterns
Monsoons
Large-scale seasonal changes in winds.
Due to differences in heating and cooling of land and water.
Similar to the smaller scale local daily land and sea breezes.
Bring heavy summer rains.

32. Seasonal Wind Patterns
El Niño
Occurs every 3 to 5 years.
Lasts 1 to 2 years.
Caused by shifts in winds and movements of warm equatorial waters.
Warmer waters occur along the equator and the west coast of South America causing the wind patterns to shift from west to east.
Impacts weather patterns in North America.