The Dynamic Earth

External Radiant Energy From the Sun Drives Atmospheric and

Hydrospheric Processes

Questions

1. How does the greenhouse effect increase surface temperature of the Earth? What would happen to the temperature of the Earth if the concentration of greenhouse gases would increase or decrease?

2. What does the Earth’s magnetic field protect us from? Does the Earth’s magnetic field extend beyond the atmosphere?

3. What would happen to our atmosphere without the magnetic field?

4. What is ozone and where is the ozone layer found?

5. From what does the ozone layer protect us and how does this layer protect us?

6. How does the Earth’s atmosphere and hydrosphere respond to differences in temperature on the Earth?

7. What produces winds?

8. What is the Coriolis Effect and which three wind belts do they produce?

What does dynamic mean?

• Ever changing in varying degrees of intensity.

• What is the source of the Earth’s dynamic nature?

• A constant flow of external and internal energy.• External Sources of Energy

– Sunlight (Electromagnetic Radiation)

• Internal Sources of Energy (earth was hot when it started)– Energy from Earth’s formation

• Extraterrestrial impacts• Gravitational contraction/compression

– Decay of radioactive elements (Uranium, for example) This supplies internal energy to the earth to mostly compensate for any transfers into space.

Fig. 1-12, p. 15

The Mechanism for Plate Motion is Convection in the Mantle

Four Layers of the Earth’s Atmosphere

• Thermosphere (oxygen absorbs solar radiation and greatly increases the temperature)

• Mesosphere (cools with altitude)• Stratosphere (contains the ozone layer,

warms with altitude due to ozone layer absorbing UV rays)

• Troposphere (weather layer, cools with altitude) Base-ground level

http://www.vtaide.com/png/atmosphere.htm

http://www.vtaide.com/png/atmosphere.htm

Atmospheric Layers

• Four Layers– Thermosphere (outermost layer, receives intense solar

radiation)– Mesosphere (coldest layer)– Stratosphere (contains the ozone layer, warmer due to

absorption of ultra-violet light)– Troposphere (the weather layer, the densest layer)

• Also, the Ionosphere (forms due to the interaction of cosmic radiation from the Sun with the faint nitrogen and oxygen concentration in the thermosphere)

Earth’s Atmospheric CompositionTable 1: Average composition of the

atmosphere up to an altitude of 25 km.

Gas Name Chemical

Formula Percent

Volume

Nitrogen N2 78.08%

Oxygen O2 20.95%

*Water^ H2O 0 to 4%

Argon Ar 0.93%

*Carbon dioxide^

CO2 0.0360%

Neon Ne 0.0018%

Helium He 0.0005%

*Methane^ CH4 0.00017%

Hydrogen H2 0.00005%

*Nitrous oxide^

N2O 0.00003%

*Ozone O3 0.000004%

* variable gases ^ greenhouse gases

Source: http://www.eoearth.org/article/Atmospheric_composition

All of these make up less than 1% of the Earth’s atmosphere!!

Atmospheric Evolution

• Primordial atmosphere contained mostly carbon dioxide and nitrogen, with some ammonia and hydrogen—volcanic gases.

• 2.5 billion years ago, a change occurred, plant cells algae, began to consume carbon dioxide and give off oxygen (photosynthesis)

• Atmosphere gradually filled with oxygen• 350 million years ago…basically same level of

oxygen as today.

Earth’s Protection System

• Ozone Layer (UV ray absorber/shield)

• Greenhouse Effect (Thermal insulating blanket produced by greenhouse gases)

• Earth’s Magnetic Field (Solar wind blocker and atmospheric erosion protector)

Without the Ozone Layer

• No terrestrial life (UV rays are dangerous to life: DNA destroyed for example)

Ozone Layer

• Ozone absorbs the majority of incoming ultra-violet light from the Sun.

• Ozone is composed of three oxygen atoms, and is toxic to humans.

• Ozone holes or thinning is primarily caused by CFCs (chlorofluorocarbons)—used in aerosol sprays, now banned worldwide.

• Some evidence of the “healing” of the ozone layer is observed, however, it is estimated that it should recover in another 2-3 decades without CFCs.

Without the Magnetic Field

• Atmosphere would be eroded by the solar wind, and cosmic radiation (high-speed high energy electrons and protons from the Sun) would harm living organisms and strip away the ozone layer.

Solar Wind and Magnetic Field

The Earth’s Magnetic Field Protects us from The Earth’s Magnetic Field Protects us from the Solar Windthe Solar Wind

Solar wind consists of charged particles moving away from the Sun.

Ingredients for the Aurora

• Planet must have a magnetic field

• Planet must receive charged particles from Sun in the solar wind (protons, electrons, alpha particles)

• Planet must have an atmosphere

Near the magnetic poles, these particles sometimes leak into our atmosphere, causing the gases to glow. This is known as the aurora.

Production of an Aurora

• Some high-speed charged particles from the Sun’s solar wind are drawn towards the poles by the Earth’s magnetic field lines.

• The particles interact with gas particles in the atmosphere, causing them to glow.

Without the Greenhouse Gases

• Earth would much colder and iced over (-27 degrees C avg. surface temperature, compared to 14-15 degrees C with greenhouse gases)

Greenhouse Effect• The surface of the Earth absorbs mostly shorter wavelength

visible light from the Sun. Due to the increase in temperature, the Earth then reradiates energy as infrared light.

• The presence of greenhouse gases, CO2 and H2O and methane (CH4) and a few other trace gases, serve to absorb some of the infrared light radiated from the Earth’s surface.

• Visible light’s wavelength is too short to be absorbed by these greenhouse gases on the way in, but infrared light’s wavelength is longer and can be absorbed.

• This leads to increased surface temperature.

13. How does the greenhouse effect help keep the Earth’s surface warm?

• The greenhouse effect is the warming of a planet’s surface due to the trapping of terrestrial long-wave infrared radiation by the greenhouse gases in the planet’s atmosphere.

Radiant Heat and Atmospheric- Heat Flow

• Which part of the Earth receives the most energy from the Sun?

• The equator!

• How does this influence the flow of heat on Earth?

• Since heat flows from hot to cold, the heat flows away from the equator towards the poles.

Earth’s Thermal Energy Cycle

• Excess heat (thermal energy) accumulates in the vicinity of the Earth’s equator.

• This heats the atmosphere and the Earth’s oceans.

• Heat or thermal energy is moved away from the equator to the poles to equalize the temperature of the Earth—Earth strikes a balance.

Earth’s Thermal Energy Cycle

• How does the Earth correct for this imbalance in thermal energy (hot equator, cold poles)?– Winds form a convection current from the equator to

poles (warm air moves to the poles, is cooled and returns to be heated).

– Ocean currents carry warm water to the poles and, when cooled, the cooler water from the poles circulates to the equator to be heated again.

Atmosphere Pressure and Wind

• What causes the wind?• Differences in atmospheric pressure.• What causes differences in atmospheric pressure?• Differences in the heating of the Earth’s surface.• What causes differences in the heating of the

Earth’s surface?• Three reasons

– Angle of the sunlight striking the Earth’s surface– Duration of the sunlight– Ratio of sunlight being reflected vs. absorbed

Wind Belts and the Coriolis Effect

• Without the rotation of the Earth, two main convection cells would operate, from equator to poles.

• With the rotation, the winds are deflected either east or west, due to the Coriolis effect.

• Winds from the poles are deflected to the west, winds from the equator are deflected to the east.

• These are the prevailing winds (trade winds, westerlies and polar easterlies)

Two Atmospheric Convection Cells

Heat flow by Convection—

Warmer atmosphere rises and moves towards the poles, sinks at the poles and moves back toward the equator

With no rotation of Earth

Coriolis Effect breaks up the two hemispheric convection cells into 6 distinct global wind belts

http://www.astronomynotes.com/solarsys/coriolisc.gif

Coriolis Effect

• The apparent change in the direction of an object’s path due to the Earth’s rotation.

• http://www.wiley.com/college/strahler/0471480533/animations/ch07_animations/animation2.html.

Coriolis Effect

http://www.grossmont.edu/judd.curran/images/coriolis.gif

-Apparent motion of objects in northern hemisphere as observed from their origin is to the right.

-Apparent motion of objects in the southern hemisphere as observed from their origin is to the left.

Coriolis Effect

http://www.cartage.org.lb/en/themes/sciences/Astronomy/Solarsystem/TheSolarsystem/theearth/ConsequencesofRotation/coriolis.gif

-Winds that move toward the poles move east (Earth is spinning slower relative to the speed of the wind—wind moves ahead)

-Winds that move toward the equator move west (Earth is spinning faster relative to the speed of the wind—wind falls behind.

Global Wind Belts

The two atmospheric convection cells that move from the equator to the poles are modified by the Coriolis Effect because the Earth rotates. This forms the global wind belts.

1) Polar easterlies 2) Prevailing westerlies 3) Tropical easterlies

Coriolis Effect and Winds

-Winds in the northern hemisphere curve clockwise-Winds in the southern hemisphere curve counterclockwise.

• Rising air leads to low pressure near the surface and sinking air leads to high pressure near the surface. This leads to semi-permanent pressure zones on the earth because of these three circulation cells. See figure 2. Figure 2 In addition, as air travels along, it experiences the coriolis force because of earth's rotation. This force tends to deflect motion the the right in the northern hemisphere and to the left in the southern hemisphere. The combination of the three (six) major circulation cells, the semi-permanent pressure zones and the coriolis force cause the generalized circulation patterns seen in the figures. (i.e. "Easterlies" and "Westerlies")

Ocean Currents

• Surface ocean currents circulate throughout the Earth.

• Surface ocean currents are produced by the prevailing wind belts blowing over the water’s surface.

• Warm water currents transfer heat towards the poles

Water’s capacity to store heat affects the global climate.

Water stores and hold heat well because of its high specific heat.

21.7 The High Specific Heat Capacity of Water

Gulf Stream brings warm water northeast from the Caribbean.

The Gulf Stream (warm water from equator)

---meets ---

The Labrador Current (cold water from polar region)

Gulf Stream

Labrador Current

Thermal Front