Chapter 17 The Atmosphere: Structure and Temperature
Intro. to unequal heating… • Why is it colder toward the poles than it is near the equator? • Does this relate to climate? • First off, let’s describe…
Weather Defined • Weather is …… The state of the atmosphere at any time and place is. • Continually changing. • The combination of Earth’s motions and energy from the sun produce a variety of weather.
Climate Defined • Climate is…. based on observations of weather that have been collected over many years. • Climate helps describe a place or region. • Often refers to average temperature and rainfall amounts at given times of the year.
Composition of the Atmosphere • Earth’s early atmosphere was much different. • Volcanic activity provided most of the original gases. • Oxygen didn’t start to accumulate about 2.6 billion years ago. • Photosynthetic organisms began
Interactive Atmosphere • The atmosphere continuously exchanges materials with the ocean and life on Earth.
Major Components Air is a….. A. compound B. Mixture MIXTURE
Composition of Atmosphere • Air is mostly gas with a few variable components. • Gases include: • Nitrogen – 78% • Oxygen – 22% • The remaining 1% includes: • Argon - .93% • CO2 - .039% - Although only a small amount, this gas absorbs energy given off by Earth. • This is very important in heating the atmosphere.
Variable Components These components vary from time to time and from place to place……. Variable components include: • Water vapor • Dust • Ozone
Variable Components • These components can have significant effects on weather and climate. • The water vapor varies from almost none to about 4% by volume.
Water Vapor Why is this small amount so significant? • Water vapor is the source of all clouds and precipitation. • It also absorbs heat given off by the Earth and absorbs some solar energy.
Movement of Atmosphere • Movements of the atmosphere allow a large quantity of solid and liquid particles to be suspended within it. • Microscopic dust can stay in the atmosphere for many years. Example: Volcanic dust may stay in the atmosphere for 100 years.
Other substances include: • Sea salts • Fine soil blown into the atmosphere • Smoke • Soot • Pollen • Microorganisms
Ozone • Ozone – is a form of oxygen that combines three oxygen atoms (O3) into each molecule. • REMEMBER: This is not the form of oxygen we breathe.
Ozone • Ozone is not evenly distributed. It is concentrated about 10-50 km above the Earth’s surface. • At this altitude 02 is split into single atoms when they absorb ultraviolet radiation. • Ozone forms from the collision of single oxygen atoms (0) with a molecule of 02. 0 + 02 = 03
UV rays are very, very harmful • Ozone is crucial to life on Earth. • Imagine what Earth would like if all the sun’s ultra-violet radiation was not filtered out.
Human Influence Air pollutants are airborne particles and gases that occur in large enough quantities to endanger the health of organisms. • Primary pollutants include: • CO carbon monoxide – 49.1% • Nitrogen oxides – 14.8% • Volatile organics – 13.6% • Sulfur oxides – 16.4% • Particulates – 6%
Air Pollution Sources include: • transportation • fuel combustion to produce electricity • industrial processes • solid waste disposal
Secondary Pollutants • Secondary pollutants form in the atmosphere when reactions occur between primary pollutants. Example: After sulfur dioxide enters the atmosphere it combines with oxygen to form sulfur trioxide. Sulfur trioxide combines with water to form H2SO4 or sulfuric acid.
Smog • Example: Some reactions are triggered by sunlight and are called photochemical reactions. • When nitrogen oxides absorb solar energy a chain of complex reactions begins. • If certain volatile organic compounds are present, secondary products form that are reactive, irritating, and toxic….. smog
Height and Structure of the Atmosphere • The atmosphere becomes less dense (thins) as you travel away from Earth until there are too few gas molecules to measure.
Pressure Changes • Atmospheric pressure is simply the weight of the atmosphere. • At sea level the average air pressure is just over 1000 millibars (14.7 lbs/in2). • One half of the atmosphere lies below the altitude of 5.6 kilometers. • Above 100 kilometers, only .00003% of the gases exist. • Therefore, as you gain altitude there is less air pressure.
Temperature Changes • Most of the time temperature decreases with altitude. • The atmosphere can be divided into four vertical layers
Layers of the Atmosphere • The atmosphere is divided into four layers based on temperature changes that occur at different distances above the Earth’s surface. • The Troposphere • The Stratosphere • The Mesosphere • The Thermosphere
The Troposphere • The troposphere is the lowest layer of the atmosphere in which temperature drops at a constant rate as altitude increases. • This is the part of the atmosphere where weather conditions exist. • The troposphere is Earth’s densestatmospheric layer and extends to 18 km above Earth’s surface.
The Stratosphere • The stratosphere is the layer of the atmosphere that lies immediately above the troposphere and extends from about 10 to 50 km above the Earth’s surface. • Temperature rises as altitude increases because ozone in the stratosphere absorbs the sun’s ultraviolet (UV) energy and warms the air.
The Stratosphere • Ozone is a gas molecule that is made up of three oxygen atoms. • Almost all of the ozone in the atmosphere is concentrated in the stratosphere. • Because ozone absorbs UV radiation, it reduces the amount of UV radiation that reaches the Earth. • UV radiation that does reach Earth can damage living cells.
The Mesosphere • The layer above the stratosphere is the mesosphere. • This layer extends to an altitude of about 80 km. • This is the coldest layer of the atmosphere where temperatures have been measured as low as –93ºC.
The Thermosphere • The atmospheric layer located farthest from Earth’s surface is the thermosphere. • Here, nitrogen and oxygen absorb solar radiation resulting in temperatures measuring above 2,000 ºC. • The air in the thermosphere is so thin that air particles rarely collide, so little heat is transferred, and would therefore not feel hot to us.
The Thermosphere • The absorption of x-rays and gamma rays by nitrogen and oxygen causes atoms to become electrically charged. • Electrically charged atoms are called ions, and the lower thermosphere is called the ionosphere. • Ions can radiate energy as light, and these lights often glow in spectacular colors in the night skies near the Earth’s North and South Poles.
Earth – Sun Relationships • How much of the sun’s energy actually reaches the Earth? (1/2,000,000,000) One – two billionth. • This energy is not evenly distributed, it varies with latitude, time of day, and season of the year. • Depends on the angle the sun’s rays hit the earth.
Uneven Heating • This uneven heating causes the winds and drives the ocean currents. • Think of how ocean currents try to even the distribution of heat around the Earth (Oceanography again?)
Earth’s Motions • The Earth rotates once in about 24 hours. • It orbits the sun at about 113,000 km/hr (70,000 mph) in an elliptical orbit.
Earth’s Orientation • Seasonal changes occur because the Earth is tilted 23.50. • The constant movement of the Earth causes solar noon to vary up to 470. Example: New York City has a maximum solar angle 0f 73.50. As you can see the sun is never actually straight (900) overhead. This occurs on June 21st. • Six months later solar noon reaches a minimum of 26.50.
Length of Day • The farther north you are from the equator on the summer solstice, the longer the period of daylight. When your reach the Arctic Circle, at 66.5 degrees N. latitude the length of daylight is 24 hours.
17.2 - Heating the Atmosphere • The concept of heat is often misunderstood…. • Heat is the energy transferred from one object to another because of a difference in their temperatures. • Temperature is the measure of the average kinetic energy of the individual atoms or molecules in a substance
Energy Transfer • When energy is transferred to the gas atoms and molecules in air, those particles move faster and air temperature rises. • When air transfers energy to a cooler object, its particles move slower, and air temperature drops.
Energy Transfers as Heat • Three mechanisms of energy transfer as heat are: • Conduction – is the transfer of heat through matter by molecular activity. • Good conductors include metals. Air is a poor conductor of heat. • Conduction only occurs between the air and the Earth’s surface that is direct contact with the air. • For the atmosphere, conduction is the least important mechanism of heat transfer.
Convection • Convection – is the transfer of heat by mass movement or circulation with in a substance. • Convection takes place in fluids like the ocean and air where the atoms and molecules are free to move about. • Convection also occurs in solids that behave like fluids like materials in the mantle.
Four Laws of Radiation Four laws the govern radiation: 1. All objects, at ANY temperature, emit radiant energy. • The sun, the Earth, the poles 2. Hotter objects radiate more total energy per unit area than colder objects do.
Laws Cont. 3. The hottest radiating bodies produce the shortest wavelengths of maximum radiation. • The sun emits energy within the visible light range (6000 oC so maximum energy at 0.5 μm) while Earth emits light in the infrared range (max. @ 10 μm)