BIOL 4120: Principles of Ecology Lecture 3: Physical Environment: Climate

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BIOL 4120 Principles of Ecology Lecture 3
Physical Environment Climate

• Dafeng Hui
• Office Harned Hall 320
• Phone [phone]
• Email dhui_at_tnstate.edu

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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.

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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

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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 Earths surface towards south.
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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).
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.).
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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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• 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.

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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
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3.5 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

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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.
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3.6 Topography influences regional and local
patterns of precipitation

• Rain shadow

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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.
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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 (aspectdirection
a slope face, surface or underground, beneath
vegetation or not), light, temperature, air
conditions or wind movement, moisture etc.
Vegetation also moderate microclimates.
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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

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3.9 Climate and global vegetation
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Global pattern of PPT and vegetation
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Conclusions

• 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 Earths surface.
• These patterns determine global vegetation
  distribution
• No one ecosystem type dominates globe, but
  instead different types vegetation adapted to
  different climatic conditions

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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.
30º N
Equator
30º S