Chapter 17 The Atmosphere: Structure and Temperature
Weather is ……
The state of the atmosphere at any time and place is.
The combination of Earth’s motions and energy from the sun produce a variety of weather.
based on observations of weather that have been collected over many years.
Climate helps describe a place or region.
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.
The atmosphere continuously exchanges materials with the ocean and life on Earth.
Air is a…..
Air is mostly gas with a few variable components.
Gases include :
Nitrogen – 78%
Oxygen – 22%
The remaining 1% includes :
Argon - .93%
CO 2 - .039% - Although only a small amount, this gas absorbs energy given off by Earth.
This is very important in heating the atmosphere.
These components vary from time to time and from place to place…….
Variable components include :
These components can have significant effects on weather and climate.
The water vapor varies from almost none to about 4% by volume.
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.
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 :
Fine soil blown into the atmosphere
Ozone – is a form of oxygen that combines three oxygen atoms (O 3 ) into each molecule.
REMEMBER: This is not the form of oxygen we breathe.
Ozone is not evenly distributed. It is concentrated about 10-50 km above the Earth’s surface.
At this altitude 0 2 is split into single atoms when they absorb ultraviolet radiation.
Ozone forms from the collision of single oxygen atoms with a molecule of 0 2 .
Ozone is crucial to life on Earth.
Imagine what Earth would like if all the sun’s ultra-violet radiation was not filtered out.
The Changing Hole in the Ozone Layer
Air pollutants are airborne particles and gases that occur in large enough quantities to endanger the health of organisms.
Primary pollutants include:
CO – 49.1%
Nitrogen oxides – 14.8%
Volatile organics – 13.6%
Sulfur oxides – 16.4%
Particulates – 6%
Sources include :
solid waste disposal
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 H 2 SO 4 or sulfuric acid.
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 thins as you travel away from Earth until there are too few gas molecules to measure.
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 .
Most of the time temperature decreases with altitude.
The atmosphere can be divided into four vertical layers
Earth – Sun Relationships
How much of the sun’s energy actually reaches the Earth?
One – two billionth .
This energy is not evenly distributed, it varies with latitude, time of day, and season of the year.
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?)
The Earth rotates once is about 24 hours.
It orbits the sun at about 113,000 km/hr in an elliptical orbit.
Seasonal changes occur because the Earth is tilted 23.5 0 .
The constant movement of the Earth causes solar noon to vary up to 47 0 .
Example: New York City has a maximum solar angle 0f 73.5 0 .
As you can see the sun is never actually straight (90 0 ) overhead.
This occurs on June 21 st .
Six months later solar noon reaches a minimum of 26.5 0 .
Solstices and Equinoxes
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.
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
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 Transfer 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 – 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.
All forms of light that originates at the sun form the electromagnetic spectrum.
All forms and wavelengths of light travel at a speed of 300,000 km/sec.
Radiation – travels out in all directions for its source.
Radiant energy can travel through the vacuum of space.
Solar energy reaches Earth by?
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.
3. The hottest radiating bodies produce the shortest wavelengths of maximum radiation.
The sun emits energy with the visible light range while Earth emits light in the infrared range.
4. Objects that are good absorbers of radiation are good emitters as well.
The atmosphere does not absorb certain wavelengths or radiation, but is a good absorber of other wavelengths.
Now that you are an expert on heat transfer……………. Write a small description that explains how this water is being heated… You must include the terms you think heat the water like radiation, conduction, and convection Send via email or bring in a hard copy.
What Happens To Solar Radiation ?
When radiation strikes an object, there are usually three different results :
1. Some energy is absorbed by the object.
When absorption occurs radiant energy is converted to heat energy.
2. Substances such as water and air are transparent to certain wavelengths of radiation.
Energy that is transmitted does not contribute energy to the object.
3. Some radiation may bounce off the object without being absorbed or transmitted.
Reflection and Scattering
Reflection occurs when light bounces off an object.
The reflected radiation has the same intensity as the incident radiation.
Scattering produces a large number of weaker rays that travel in different directions.
About 30% of the radiant energy that reaches Earth’s atmosphere is reflected back into space.
This energy is lost and does not heat the Earth or its atmosphere.
Some dust particles and gas molecules scatter some incoming radiation in all directions.
This is how some light reaches beneath a shade tree.
Scattering also accounts for the brightness and even the color of the atmosphere.
About 50% of the energy that strikes the top of the atmosphere reaches the Earth’s surface and is absorbed.
Most of this energy is reradiated skyward.
Since the Earth is cooler than the sun it emits longer wave radiation in the infrared range.
The atmosphere efficiently absorbs the longer wavelengths emitted by the Earth.
Water vapor and carbon dioxide are major absorbing gases.
When a gas molecule absorbs light waves, this energy is transformed into molecular motion that can be detected as a rise in temperature.
This energy can be :
Reabsorbed by other gas molecules
Absorbed by the Earth
This phenomenon has been termed the greenhouse effect .
Why Temperature Varies includes :
2. Variation in the angle of sunlight
3. Heating land and water
5. Geographic position
6. Cloud cover
7. Ocean currents
Land and Water
Different land surfaces absorb varying amounts of incoming solar radiation.
The largest contrast is between land and water.
Land heats more rapidly to higher temperatures than water.
Land also cools more rapidly and to lower temperatures that water.
Therefore, temperature variations are considerably greater over land than water.
61% of the Northern hemisphere is covered by water and 39 % land.
81% of the Southern hemisphere is covered by water and 29% land.
Which hemisphere has smaller annual temperature variations?
The Southern hemisphere
Compare the east coast of the U.S. with the west coast of England.
England has cooler summers and milder winters.
Seattle and Spokane, Washington – temperature variation occurs because of a mountain range.
Seattle has a more marine influence.
Spokane is separated from the ocean by the Cascade Range and has a more continental influence and larger temperature variation.
Temperatures tend to drop with altitude.
Cloud Cover and Albedo
Albedo is the fraction of total radiation that is reflected by any surface.
Many clouds have a high Albedo, and therefore reflect a significant portion of the sunlight that strikes them back in space.
The extent of cloud cover influences temperatures in the lower atmosphere.
At night clouds have the opposite effect. Clouds act like a blanket by absorbing outgoing radiation emitted by the Earth and reradiating a portion of it back to the surface.
Cloudy nighttime temperatures don’t drop and much as clear night temperatures.
The effect of cloud cover is to reduce the daily temperature range by lowering the daytime maximum and raising the nighttime minimum.
World Distribution of Temperatures
Isotherms - are lines on a weather map that connect points that have the same temperature.