Convection, Wind, and the Coriolis Effect How uneven heating and the Earth’s rotation drive Earth’s climate

Core Case Study Blowing in the Wind: A Story of Connections Wind connects most life on earth. Keeps tropics from being unbearably hot. Prevents rest of world from freezing. Figure 5-1

Weather & Climate Weather is a local area’s short-term physical conditions such as temperature and precipitation. Climate is a region’s average weather conditions over a long time. Latitude and elevation are the major determinants of climate.

Earth’s Current Climate Zones Figure 5-2

How the Earth Heats Radiation - transfer of heat energy by electromagnetic wave motion Conduction – transfer of energy from direct molecule to molecule contact – occurs in solids Convection – transfer of energy through moving currents – occurs in fluids (liquids & gases) Source: Atmospheric Processes: Radiation Introduction o the Atmosphere. Retrieved on September 30, 2009 from http://www.ucar.edu/learn/1_1_2_5t.htm

Solar Energy and Global Air Circulation: Distributing Heat Global air circulation is affected by the uneven heating of the earth’s surface by solar energy, seasonal changes in temperature and precipitation. Figure 5-3

What is Radiation? Source: Atmospheric Processes: Radiation Introduction o the Atmosphere. Retrieved on September 30, 2009 from http://www.ucar.edu/learn/1_1_2_5t.htm About 43% of the total radiant energy emitted from the sun is in the visible parts of the spectrum. The bulk of the remainder lies in the near-infrared (49%) and ultraviolet section (7%). Less than 1% of solar radiation is emitted as x-rays, gamma waves, and radio waves. A perfect radiating body emits energy in all possible wavelengths, but the wave energies are not emitted equally in all wavelengths; a spectrum will show a distinct maximum in energy at a particular wavelength depending upon the temperature of the radiating body. As the temperature increases, the maximum radiation occurs at shorter and shorter wavelengths. The hotter the radiating body, the shorter the wavelength of maximum radiation. For example, a very hot metal rod will emit visible radiation and produce a white glow. On cooling, it will emit more of its energy in longer wavelengths and will glow a reddish color. Eventually no light will be given off, but if you place your hand near the rod, the infrared radiation will be detectable as heat. About 43% of the total radiant energy emitted from the sun is in the visible parts of the spectrum. The bulk of the remainder lies in the near-infrared (49%) and ultraviolet section (7%). Less than 1% of solar radiation is emitted as x-rays, gamma waves, and radio waves.

What is Convection? Movement that results when heat is transferred in a fluid First, warmed fluids (like water or air) become less dense and will rise opposite to the force of gravity. Next, cooler fluid will move to replace the rising warm fluid and it will be warmed itself. This cycle repeats to mix the fluid. Convection model Julius Sumner Miller on Convection - a riot! 8

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Convection Currents Global air circulation is affected by the properties of air water, and land. Figure 5-5

Topography and Local Climate: Land Matters Interactions between land and oceans and disruptions of airflows by mountains and cities affect local climates. Figure 5-8

Temperature Inversions Cold, cloudy weather in a valley surrounded by mountains can trap air pollutants (left). Areas with sunny climate, light winds, mountains on three sides and an ocean on the other (right) are susceptible to inversions. Figure 19-5

What on Earth? Descriptions of Earth’s Convection Edmond Halley 1656-1742 reasoned that intense solar radiation heated the air near the Equator and caused it to expand and rise up. This rising air is replaced by cooler air converging on the Equator from the northern and southern hemispheres. Circulation of the air is driven by a pressure-gradient force, which causes high-pressure (cooler, more dense) air to move into regions of low-pressure (warmer, less dense) air. predicted a flow of air from the poles to the Equator where the air masses converge. Who Developed The Early Theories About The Trade Winds? The name, trade winds, derives from the Old English ”trade”, meaning path or track. The trade winds helped ensure that European sailing vessels, including those that Columbus sailed, reached North American shores. Edmond Halley (1656-1742), pictured on the left, correctly understood the role of the Sun in atmospheric circulation. He reasoned that intense solar radiation heated the air near the Equator and caused it to expand and rise up. This rising air is replaced by cooler air converging on the Equator from the northern and southern hemispheres. Circulation of the air is driven by a pressure-gradient force, which causes high-pressure (cooler, more dense) air to move into regions of low-pressure (warmer, less dense) air. Under static conditions, fluids reach equilibrium when pressure is the same at each depth. His theory predicted a flow of air from the poles to the Equator where the air masses converge. But the explanation does not account for the steady westward flow.   George Hadley (1685-1768), was an English lawyer and amateur meteorologist, who first recognized the reason the trade winds, preferentially blow westward. His explanation depended on the fact that Earth is a rotating sphere and that sites on the surface of rotating sphere travel with different speeds (travel different distances in equal times). Hadley earned fame by realizing that Earth's rotation played a crucial role in the direction taken by a moving airmass. He provided a description of the equatorial trade winds that was essentially correct. Weather, which describes the current state of the atmosphere, normally fluctuates daily due to a complex interplay of forces and processes. Any steady or cyclic weather phenomena could be the result a dominating process. These phenomena provide opportunities to test scientific models and hypotheses. In the following pages you will work with the equations that help us understand how objects and air masses move on a rotating sphere. Illustration Credit: Tinka Sloss, New Media Studio, Inc. 13

What on Earth? Descriptions of Earth’s Convection George Hadley 1685-1768 English lawyer and amateur meteorologist First to describe the reason the equatorial trade winds preferentially blow westward. Recognized that Earth is a rotating sphere and that sites on its surface travel with different speeds (travel different distances in equal times). Model of Earth’s convection termed the ‘Hadley cell’ in his honor. 14

Convection Cells Heat and moisture are distributed over the earth’s surface by vertical currents, which form six giant convection cells at different latitudes. Figure 5-6

Prevailing Wind Belts on the Earth

A Horizontal View 17

Gustave Gaspard de Coriolis The Coriolis Effect Gustave Gaspard de Coriolis 1792 - 1843 French mathematician, mechanical engineer, and scientist Determined simple rules for the direction of moving objects on the surface of a rotating sphere, now known as the Coriolis effect: The apparent (Coriolis) force is perpendicular to the velocity of the object and the rotation axis. A balance of forces causes objects traveling in the Northern Hemisphere to curve to the right. A balance of forces causes objects traveling in the Southern Hemisphere to curve to the left. 18

The Coriolis Effect http://www.youtube.com/watch?v=_36MiCUS1ro

Visualizing the Coriolis Effect Earth rotates at different speeds at different latitudes. v = d/t The Coriolis Model A Which site travels the greatest distance during one revolution (24 hours)? Which site has the greatest speed? B C 20

Major Wind Belts Prevailing Wind Belts of Earth The earth is encircled by several broad prevailing wind belts, which are separated by narrower regions of either subsidence or ascent. The direction and location of these wind belts are determined by solar radiation and the rotation of the earth. The three primary circulation cells are known as the: Hadley cell; Ferrel cell; and Polar cell. 21

Coriolis Effect Guide weather and storms Jet Stream Significance of Wind Belts? Guide weather and storms Jet Stream 100 mph Between 30-60º Above friction zone Influences Sailing & Navigation Deserts @ 30º Figure 5-4

Ocean Currents: Distributing Heat and Nutrients Ocean currents influence climate by distributing heat from place to place and mixing and distributing nutrients. Figure 5-7