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

1. BIOL 4120: Principles of Ecology Lecture 3: Physical Environment: Climate Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

2. 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 Gradients of vegetation in North America from east to west (a) and from South to north (b).

4. 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 • 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 (400-700 nm) Or Photosynthetically Active Radiation (PAR) longwave radiation Earth is a balanced ecosystem in term of solar energy inputs and outputs

6. Seasonality in intercepted solar radiation 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.

8. 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. 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

11. 3.2 Air temperature decreases with altitude Why? Environmental lapse rate: the rate at which temperature decreases with altitude

12. 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)