1. Dafeng Hui Office: Harned Hall 320 Phone: 963-5777
11/22/2018
BIOL 4120: Principles of Ecology Lecture 3: Physical Environment: Climate
Dafeng Hui
Office: Harned Hall 320
Phone:

2. 3.1 Solar radiation and seasonal changes
11/22/2018
Topics for this class:
3.1 Solar radiation and seasonal changes
3.2 Air temperature decreases with altitude
3.3 Global air masses circulation
3.4 Ocean currents of the world
3.5 Global precipitation pattern
3.6 Local topography influence on precipitation
3.7 Regional irregularities (El Nino and La Nina)
3.8 Microclimates

3. Species distributions are often determined by physical environment
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Mi-’zer-phi-te
Mesophytic
Hickory
Gradients of vegetation in North America from east to west (a) and from
South to north (b).

4. 11/22/2018
The next question: What determines the characteristics of the physical environment (particularly air and water conditions)?
Seasonality?
Rainfall patterns?
Temperature difference?
Air & water circulation patterns?
The driving factor is the energy input to Earth system: solar radiation

5. 3.1 Earth intercepts solar radiation
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3.1 Earth intercepts solar radiation
All life requires energy to sustain itself
With very few exceptions, all life on earth is dependent on solar energy
Life on Earth exists because it’s fitness is optimal for the environment created by solar energy
Shortwave , Visible light ( nm)
Or Photosynthetically Active Radiation (PAR)
longwave radiation
117=96+21
117=11+6
Distributions of vegetation types are mostly determined by climatic factors, specifically temperature and ppt. thus it is quite important to understand the distributions and variation of these factors. The driving factor of climate change is solar radiation.
In general, the input and output of solar energy to earth is balanced. But human activity enhanced greenhouse effect, ……
Earth is a balanced ecosystem in term of
solar energy inputs and outputs

6. Seasonality in intercepted solar radiation
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Seasonality in intercepted solar radiation
The amount of solar energy intercepted at any point on earth’s surface varies markedly with latitude.
Why? 1. high latitudes, radiation hits the surface at a steeper angle, spreading sunlight over a large area. 2. radiation travel through a deeper layer of air, reflect more back to atmosphere.
These is also a seasonal variation in the intercepted solar radiation. Why do we see seasonal changes in most of places?
Earth’s axis is tilted at an angle of 23.5oC. It is this tilt that is responsible for the seasonal variations in T and daylength.
While Earth orbits around the sun, earth rotates about an axis that passes through the north and south poles, create day and night cycles.
Earth travels about the sun in a plane called the ecliptic.
Earth’s axis of spin is not perpendicular to the ecliptic.
Solstice, vernal, autumnal
Equinox
Tropic of Cancer (latitude 23.5ºN), & Tropic of Capricorn (23.5ºS) defined by extreme latitudes at which sun is directly overhead annually--summer & winter solstice, respectively. This corresponds with 23.5º angle of tilt of Earth. Thus “solar equator” (region of maximum solar input) moves relative to latitude seasonally.

7. Seasonality arises strictly because of tilted axis of Earth’s rotation (spin) relative to plane of Earth’s revolution around sun: intercepted solar radiation peaks in N. hemisphere June 22, in S. hemisphere December 22.
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Why four seasons and solar radiation variation
Spring and fall sssss, sunlight hits equator directly
Summer solsssssss, sun light hits north xx directly at Tropic of Cancer
Winter solstice, sun light hits Tropic of Capricorn firectly

8. Variation in solar radiation on Earth is quite large
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Variation in solar radiation on Earth is quite large
Compare a temperate region with a tropical region
Much greater variation in temperate region
Poles are not included but see high altitude

9. 11/22/2018
Energy input to atmosphere & Earth’s surface via solar radiation drives the annual T: maximal at equator, & declines to 40% of maximal values at high latitudes.

10. Mean Annual Temperature change with latitude and season
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Mean Annual Temperature change with latitude and season
Winter and summer: isoclines of T
Dense means steep and large changes: large gradient in winter than in summer.
Why? Jan: sun light shines directly at 23.5 S (tropic of Capricorn)
July: N (tropic of Cancer)

11. 3.2 Air temperature decreases with altitude
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3.2 Air temperature decreases with altitude
Why?
These are seasonal and temporal air temperature variations. Air T also
According to the T change, atmospheric scientist distinguished the atmosphere into 4 regions. What we are interested is the troposphere zone.
Environmental lapse rate: the rate at which temperature decreases with altitude

12. Air temperature decreases with altitude
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Air temperature decreases with altitude
Two reasons:
Decreases in air pressure and density, less heat generated;
Adiabatic cooling: The decrease of air T through expansion.
Adiabatic lapse rate: rate of T change with elevation, depends on moisture in the air(10 oC per 1000m dry, 6oC for wet air)
Air has weight. High atmospheric pressure on the surface, Atmospheric pressure decreases with altitude increase.
When a vol of air warms at surface, it becomes buoyant and rises. As the volume of air rise, the decrease of air pressure cause it to expand and cool.
This decrease in air temperature through expansion, rather than through heat loss to the surrounding atmosphere is call adiabatic cooling.