Earth Science

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.