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: 963-5777 Email: dhui@tnstate.edu

3.3 Air masses circulate globally 4/27/2017 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)

Three cells and trade wind belts 4/27/2017 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)

4/27/2017 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.

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). 4/27/2017 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.).

3.4 Global ocean currents movement 4/27/2017 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)

4/27/2017 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.

Air moisture and temperature 4/27/2017 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).

3.5 Global pattern of precipitation 4/27/2017 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.

4/27/2017 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.

4/27/2017 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.

3.6 Topography influences regional and local patterns of precipitation 4/27/2017 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)

4/27/2017 Same for the Hawaiian Islands.

3.7 Irregular variations in climate occur at the regional scale 4/27/2017 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.

4/27/2017 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.

4/27/2017 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.

4/27/2017 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.

Most organisms exist in a microclimate that is optimal 4/27/2017 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

3.9 Climate and global vegetation 4/27/2017 3.9 Climate and global vegetation

Global pattern of PPT and vegetation 4/27/2017 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.

Conclusions 4/27/2017 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

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. 4/27/2017 30º N Equator 30º S