1. Dafeng Hui Office: Harned Hall 320 Phone: 963-5777
4/27/2017
BIOL 4120: Principles of Ecology Lecture 3: Physical Environment: Climate
Dafeng Hui
Office: Harned Hall 320
Phone:

2. 3.3 Air masses circulate globally
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3.3 Air masses circulate globally
The blanket of air surrounds the planet – atmosphere – is not static
It is in a constant state of movement, driven by the rising and sinking of air masses and the rotation of the Earth on its axis.
Air temperature changes (global, seasonal, altitude), next precipitation (air movement influence)

3. Three cells and trade wind belts
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Coriolis effect:
Deflection in the pattern of air flow.
Clockwise movement in N hemisphere, counterclockwise in S. Hemisphere.
Three cells and trade wind belts
These air movements create global precipitation pattern
The equatorial region receives the largest annual input of solar radiation,. Warm air rises because it is less dense than the cooler air above it.
(warm air rises: we can not see in the air, but can in the water)
The Coriolis Force causes winds moving north or south latitudinal to deflect to the right in the Northern Hemisphere, and deflect to the left in the Southern Hemisphere. This force causes the “trade winds” moving from higher latitudes towards ITCZ to come from northeast direction north of equator (northeast trade winds) and from southeast direction south of equator (southeast trades).
Trade wind: 17-th mechant sailors used them to reach the Americas from Europe (northeast in N. Hempsphere)

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Major latitudinal displacements of surface air currents: convection currents drive Hadley cells, pulling air at surface into Inter-Tropical Convergence Zone, ITCZ); Ferrel Cells driven by low pressure zone at 20º-30º lat.; Midlatitude westerlies converge into jet stream; polar cells driven by high pressure (cold) flows out of polar region along Earth’s surface towards south.

5. The thermal equator, oscillating latitudinally with seasons, drives low latitude patterns of rainfall by establishing zones of low pressure (high rainfall) and high pressure (low rainfall).
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The hadley cell (centered on thermal equator) depends on convection currents with updrafts that cause low latitude rainforests, and downdrafts that cause subtropical hot deserts (20º - 30º N, S lat.).

6. 3.4 Global ocean currents movement
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3.4 Global ocean currents movement
Surface water movements in the ocean is dominated by the global pattern of the prevailing winds (and solar energy)

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Current: systematic patterns of water movement
Gyre (j-I-e)
Ocean currents also affect climate, sometimes very dramatically (source of energy movement too)
Each ocean is dominated by great circular water movement, or gyres. Gyres move clockwise in the N. Hemisphere and counterclockwise in the S. Hemisphere (Coriolis effect).
Warmer water moves away from equator and cold water moves towards equator.

8. Air moisture and temperature
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Air moisture and temperature
Evaporation: water to vapor
Condensation: from water vapor to water
Vapor pressure: amount of pressure water vapor exerts independent of pressure of dry air.
Saturated vapor pressure: vapor pressure of air at saturation.
Absolute humidity; amount of water in a given volume of air.
Relative humidity: RH
Water is closely related to energy changes, as if water changes from one state to another, energy absorption or release is related. The amount of energy relased or absorbed (per gram) during a change of state is known as LATEN HEAT.
Evaporation: transformation from a liquid state to gaseous state: require energy.
Condensation: transformation of water vapor to a liquid state, release energy.
…………
Rain: if air cools while the actual amount moisture it holds remains constant, then RH increase as the Saturated VP decrease. If the air cools to a point where actual pressure exceeds the saturated VP, moisture in the air condense and form clouds. As soon as particulars of water or ice in the air become too heavy to remain suspended, precipitation falls.
If not in the air (as in the morning of fall), we see Dew. (Dew point temperature).

9. 3.5 Global pattern of precipitation
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3.5 Global pattern of precipitation
By bring together patterns of temperature, winds, and ocean currents, we are ready to understand the global pattern of precipitation.

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Temporal variation in precipitation (e.g., Intertropical Convergence Zone shift)
Shifts of ITCZ produce rainy seasons and dry seasons in the tropics
Global pattern, how about temporal change?
ITCS is the narrow region where the northeasterly trade winds meet the southeasterly trade winds near the equator, charactere
d by heavy precipitation.

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Patterns of temporal variation in climate at the Southeast Asia region:
Seasonal changes in T with the rotation of Earth about the sun, and the migration of the ITCZ with the resulting seasonality of rainfall in the tropics and monsoons in southeast Asia.

12. 3.6 Topography influences regional and local patterns of precipitation
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3.6 Topography influences regional and local patterns of precipitation
Rain shadow:
More moisture on windward sides of mountains than leeward (e.g., desert areas on southeast side of Caribbean Mts., on eastern side Cascades, Rockies)

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Same for the Hawaiian Islands.

14. 3.7 Irregular variations in climate occur at the regional scale
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3.7 Irregular variations in climate occur at the regional scale
Irregular variations (Little Ice Age: cooling between mid-14 to mid-19th century)
(El Nino and La Nina)
El Nino: an abnormal warming of surface ocean waters in the eastern tropical Pacific.
El Nino-Southern Oscillation (ENSO): An oscillation in the surface pressure between the southeastern tropic Pacific and the Australian-Indonesian regions.

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Normal conditions, strong trade winds move surface water westward. As the surface currents move westward, the water warms. The warmer water of the western Pacific causes the moist maritime air to rise and cool, bringing abundant rainfall to the region;
ENSO: Trade winds slacken, reducing the westward flow of the surface currents. Rainfall follows the warm water eastward, with associated flooding in Peru and drought in Indonesia and Australia.
ENSO: water of the eastern Pacific are abnormally warm (El Nino), sea level pressure drops in the eastern Pacific and rises in the west. The reduction of pressure gradient is accompanied by a weakening of the low-latitude easterly trades.

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La Nina: injection of cold water becomes more intense than usual, causing the surface of eastern Pacific to cool. Results in droughts in South America and heavy rainfall in Australia.

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3.8 Microclimates
Microclimates defines the local, small scale conditions in which organisms live.
These conditions include: topography (aspect=direction a slope face, surface or underground, beneath vegetation or not), light, temperature, air conditions or wind movement, moisture etc.
Vegetation also moderate microclimates.

18. Most organisms exist in a microclimate that is optimal
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Most organisms exist in a microclimate that is optimal
Scale of climate in hundreds of kilometers
Scale of microclimate can vary from meters to kilometers to tens of kilometers

19. 3.9 Climate and global vegetation
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3.9 Climate and global vegetation

20. Global pattern of PPT and vegetation
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Global pattern of PPT and vegetation
By bring together patterns of temperature, winds, and ocean currents, we are ready to understand the global pattern of precipitation.

21. Conclusions
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With a few basic physical principles (solar radiation as energy, air movements, convection currents) one can explain major patterns of temperature, rainfall, seasonality, ocean currents on Earth’s surface.
These patterns determine global vegetation distribution
No one ecosystem type dominates globe, but instead different types vegetation adapted to different climatic conditions

22. The foregoing principles and forces explain much of the global patterns in vegetation types (depending on temperature, moisture): Wetter vegetation (forests) green, drier (grassland, desert) tan to brown, cold (arctic, alpine) areas white.
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30º N
Equator
30º S