1. Climate and Weather
Chapter 7

2. WEATHER & CLIMATE
Weather is an all-encompassing term used to describe all of the many and varied phenomena that can occur in the atmosphere of a planet. The term is normally taken to mean the activity of these phenomena over short periods of time, usually no more than a few days in length.
Average atmospheric conditions over significantly longer periods (30+ years) are known as climate.
Because the Earth's axis is tilted (not perpendicular to its orbital plane), sunlight is incident at different angles at different latitudes: higher latitudes have a lower angle of incidence, which results in less heating than at lower latitudes nearer the equator
A secondary cause of temperature differences on the Earth is that different surface areas (such as ocean waters, forest lands, and ice sheets) have differing reflectivity, and therefore absorb and radiate different amounts of the solar energy they receive

3. The Earth Has Many Different Climates
Weather –local areas short term temperature, precipitation, humidity, wind speed, cloud cover and other physical conditions of the lower atmosphere
Climate – general atmospheric conditions measured over a long period of time

4. Climate and Weather Topics
Seasons
Solar Intensity/Latitude
Solar radiation
Convection Currents
Coriolis effect
Rain shadow effect
Jet streams
Frontal weather
Cyclonic storms
Seasonal winds
ENSO
Milankovich cycles

5. CLIMATE
The two most important aspects of climate are temperature and precipitation.
These two factors determine what type of species (biome) will be found in a given location.
The climate in an area is determined by
Latitude
Direction from which winds arrive
Proximity to large bodies of water and mountains

6. A climograph includes both the average precipitation and the average temperature data. Your climograph should look like the one below. Be sure to include a title for your graph and a key showing the symbols that represent the average precipitation and the average temperature.
Key

7. Convection Cells – Hadley Cells
Warm air rises; cold air falls
Warm air holds more moisture than cold air
When air rises, it cools; when air falls, it warms
SO, warm, moist air rises, cools, and loses moisture as rain; cool, dry air falls, warms, and picks up moisture from the ground.
Cool, dry
precipitation
warm, dry
Warm, moist

8. Air circulation in lower atmosphere is due to
Uneven heating of the earth’s surface by the sun
Rotation of the earth on its axis
Properties of air, water, and land

9. Surface Wind Currents – the Coriolis Effect
As the earth spins, it pulls on the surface air and causes it to spin in the direction of movement.
The ground spins faster at the equator than at the poles, so in any given cell, the air closer to the equator is pulled more.
This gives rise to prevailing winds that are predictable in all areas of the world. They have been used by sailors for centuries.

10. Coriolis Effect - Cont
This causes winds to form huge circular paths – clockwise in the N. Hem and counter-clockwise in the S. Hem.

11. Connections between Wind, Climate, and Biomes
Indirect form of solar energy,
part of the earth’s circulatory system for heat, moisture, plant nutrients, soil particles and long lived air pollutants
Dust blown from West Africa – soil nutrients in Amazonian rain forests, toxic air pollutants in the US

12. Redistribution of heat from the sun
Global Air Circulation
Currents
Prevailing winds
Earth’s rotation
Redistribution of heat from the sun
60°N
Cold deserts
Air cools and descends at lower latitudes.
Westerlies
Forests
30°N
Northeast trades
Hot deserts
Warm air rises and moves toward the poles.
Forests 0°
Solar energy
Equator
Air cools and descends at lower latitudes.
Southeast trades
Hot deserts
30°S
The highest solar energy input is at the equator.
Figure 7.3
Global air circulation. The largest input of solar energy occurs at the equator. As this air is heated it rises and moves toward the poles. However, the earth’s rotation deflects the movement of the air over different parts of the earth. This creates global patterns of prevailing winds that help distribute heat and moisture in the atmosphere.
Westerlies
Forests
Cold deserts
60°S
Fig. 7-3, p. 142

13. Global Convection Cells – Hadley cells
Wet areas (warm, moist air rising)
0o(equator) - TRF
60o (Seattle) - TempRF
Dry areas (cold, dry air falling)
30o - desert
90o (poles) - tundra

14. Global Air Circulation, Ocean Currents, and Biomes
Moist air rises, cools, and releases moisture as rain
Polar cap
Arctic tundra
Evergreen coniferous forest
Global Air Circulation,
Ocean Currents,
and Biomes
60°
Temperate deciduous forest and grassland
Desert
30°
Tropical deciduous forest
Equator 0°
Tropical rain forest
Tropical deciduous forest
30°
Desert
Figure 7.6
Global air circulation, ocean currents, and biomes. Heat and moisture are distributed over the earth’s surface via six giant convection cells (like the one in Figure 7-4) at different latitudes. The resulting uneven distribution of heat and moisture over the planet’s surface leads to the forests, grasslands, and deserts that make up the earth’s terrestrial biomes.
Temperate deciduous forest and grassland
6 giant convection cells
moist air rises ,cool dry air sinks
60°
Polar cap
Fig. 7-6, p. 144

15. Ocean Temperature Stratification
Figure 8-4

16. Sea Surface Temperatures
Figure 8-5

17. Oceans absorb heat from the earth’s circulation patterns : most of this heat is absorbed in tropical waters, which receive most of the sun’s heat
Heat and differences in water density (mass/unit volume) create warm an cold ocean currents.
Prevailing winds and irregularly shaped continents interrupt these currents and cause them to flow in roughly circular patterns between the continents
Clockwise – northern hemisphere
Anti clockwise – southern hemisphere

18. High density cold waters sinks and flows beneath warmer and less dense sea water
Creates a connected loop of deep and shallow ocean currents which act like a giant conveyor belt
Transfers warm and cold water between the tropics and the poles
Ocean currents are affected
by winds in the atmosphere and heat from the ocean affects atmospheric circulation

19. Greenhouse Gases Warm the Lower Atmosphere
H2O mostly visible light and some infra red
CO2 radiation and some UV radiatio
CH4 to pass through the atmosphere
N2O
Greenhouse effect – long wave length infra red radiation (heat) rises to the lower atmosphere
Human-enhanced global warming – burning fossil fuels, clearing forests
Allow visible light , infrared and UV radiation from the sun to pass through the atmosphere

20. The Earth’s Surface Features Affect Local Climates
Heat is absorbed and released more slowly by water than by land. Creates land and sea breezes
World’s oceans and large lakes moderate weather and climate
Effect of earth’s surface features
Mountains-interrupt flow of prevailing winds and movement of storms
Rain shadow effect
Cities -Microclimates bricks, concrete, asphalt absorb and hold heat and buildings block wind flow. Cars release large amount of pollutants. More haze and smog, higher temperatures and lower wind speeds

21. Rain Shadow Effect Prevailing winds pick up moisture from an ocean.
On the windward side of a mountain range, air rises, cools, and releases moisture.
On the leeward side of the mountain range, air descends, warms, and releases little moisture.
Figure 7.7
The rain shadow effect is a reduction of rainfall and loss of moisture from the landscape on the side of a mountain facing away from prevailing surface winds. Warm, moist air in onshore winds loses most of its moisture as rain and snow on the windward slopes of a mountain range. This leads to semiarid and arid conditions on the leeward side of the mountain range and the land beyond. The Mojave Desert in the U.S. state of California and Asia’s Gobi Desert are both produced by this effect.
Rain Shadow Effect
Fig. 7-7, p. 145

22. The Earth Has Many Different Climates
Prevailing winds blowing over the oceans produce mass movements of water called currents. Driven by prevaining winds and the earth’s rotation, the major oceancurrents redistribute heat from the sun from place to place., thereby influencing climate and vegetation.

23. How Does Climate Affect the Nature and Locations of Biomes?
Differences in average annual precipitation and temperature lead to the formation of tropical, temperate, and cold deserts, grasslands, and forests, and largely determine their locations.

24. Climate Affects Where Organisms Can Live
Major biomes – large terrestrial regions characterized by similar climate, soil, plants and animals. Mosaic of patches each with some basic similarities but different biological communities
Latitude and elevation
Annual precipitation
Temperature –tropical, temperate, polar

25. The Earth’s Major Biomes

26. Effects of Elevation and Latitude on Climate and Biomes
Mountain ice and snow
Tundra (herbs, lichens, mosses)
Coniferous Forest
Deciduous Forest
Latitude
Tropical Forest
Figure 7.9
Generalized effects of elevation (left) and latitude (right) on climate and biomes. Parallel changes in vegetation type occur when we travel from the equator to the poles or from lowlands to mountaintops. Question: How might the components of the left diagram change as the earth warms during this century? Explain.
Tropical Forest
Deciduous Forest
Coniferous Forest
Tundra (herbs, lichens, mosses)
Polar ice and snow
Fig. 7-9, p. 147

27. Decreasing temperature Decreasing precipitation
Cold
Polar
Tundra
Subpolar
Temperate
Coniferous forest
Decreasing temperature
Desert
Deciduous forest
Grassland
Tropical
Chaparral
Hot
Figure 7.10
Natural capital: average precipitation and average temperature, acting together as limiting factors over a long time, help to determine the type of desert, grassland, or forest biome in a particular area. Although each actual situation is much more complex, this simplified diagram explains how climate helps to determine the types and amounts of natural vegetation found in an area left undisturbed by human activities. (Used by permission of Macmillan Publishing Company, from Derek Elsom, The Earth, New York: Macmillan, Copyright © 1992 by Marshall Editions Developments Limited).
Desert
Wet
Rain forest
Savanna
Dry
Tropical seasonal forest
Scrubland
Decreasing precipitation
Fig. 7-10, p. 147

28. Mountains Play Important Ecological Roles
Majority of the world’s forests
Habitats for endemic species
Help regulate the earth’s climate – snow and ice covers reflect solar radiation back. Cool earth and off set global warming
Can affect sea levels by storing and releasing water in glacial ice. Warmer earth adds water by melting of glaciers
Major storehouses of water
Role in hydrologic cycle

29. Seasonal Winds
Many parts of the world experience seasonal winds, or wind direction reversals
Ex. monsoons (rain shadow effect)
Sirocco
Santa Anas

30. Other Intraseasonal Oscillations
Monsoons: weather pattern driven by seasonal differences in heating of land and ocean
Influences prevailing winds and weather patterns
Figure 7-22

31. El Nino (ENSO)
The winds in the Pacific normally blow across the surface of the water in the Westward direction
This causes
Rain in Indonesia, mild winters in CA, upwelling off the coast of S.Am., cold surface waters on Eastern Pac.
La Nina is an increased flow in this direction.

32. El Nino (ENSO)
In El Nino years, the winds blow across the surface in the Eastern direction
This causes
Drought in Indonesia, wet winter in CA,
no upwelling (fish and mammal die-offs),
warm surface water in Eastern Pac.

33. Fronts
A front is a boundary between two air masses of different temps (and pressures).
Warm front – approaching air is warmer than local air
Cold front- approaching air is colder than local air
Both can cause rain; cold fronts are associated with more severe weather

34. El Nino Animation
all.com/science/geoa nimations/animation s/26_NinoNina.html

35. Cyclonic storms
These are storms that are characterized by masses of rotating air caused by pressure differentials between the ground and air.
Hurricanes (typhoons and cyclones) form over water, and are much larger
Tornadoes form over land are more localized

36. Tropical Cyclones
Tropical Cyclones – south pacific, Hurricanes - atlantic, and Typhoons – west pacific (oh my!)
Formation: Carnot Cycle driven by heat and moisture from the ocean surface (sst>26.5°C)
Structure
D:\Media\Active_Figures\68_Hurricane_Morphology \68.html

37. Tropical Cyclones
low latitudes, 5-20o (not at the equator): f (coriolis parameter) important
none in SE Pacific or S. Atlantic: SSTs important
more appear in the Pacific than in the Atlantic: SSTs important

38. Tropical Cyclones and SST

39. Milankovitch Cycles Milankovitch Cycles
What are Milankovitch Cycles? Natural global warming, and cooling, is considered to be initiated by Milankovitch cycles. These orbital and axial variations influence the initiation of climate change in long-term natural cycles of 'ice ages' and 'warm periods' known as 'glacial' and 'interglacial' periods. The cycles appear to be range bound in the paleo record for the past 5 million years. Our current climate forcing shows we are outside of that natural cycle forcing range.

40. NATURAL CAPITAL DEGRADATION
Major Human Impacts on Terrestrial Ecosystems
Deserts
Soil salinization from irrigation
Depletion of groundwater
Land disturbance and pollution from mineral extraction
Grasslands
Conversion to cropland
Release of CO2 to atmosphere from burning grassland
Overgrazing by livestock
Oil production and off-road vehicles in arctic tundra
Forests
Clearing for agriculture, livestock grazing, timber, and urban development
Conversion of diverse forests to tree plantations
Damage from off-road vehicles
Pollution of forest streams
Mountains
Agriculture
Timber extraction
Hydroelectric dams and reservoirs
Mineral extraction
Increasing tourism
Urban air pollution
Increased ultraviolet radiation from ozone depletion
Soil damage from off-road vehicles
Large desert cities
Figure 7.20
Major human impacts on the world’s deserts, grasslands, forests, and mountains. Question: Which two of the impacts on each of these biomes do you think are the most harmful?
Soil destruction by off-road vehicles
Stepped Art
Fig. 7-20, p. 158