Atmosphere: a mixture of gas molecules, microscopically small suspended particles of solid and liquid, and falling precipitation.
Meteorology is the study of the atmosphere and the
processes (like cloud formation, lightning, and wind movement) that cause what
we refer to as “weather”.
Photosynthesis, Respiration, and Carbon Dioxide
The Balance Sheet
Plant growth requires
Plant decay releases carbon dioxide to the atmosphere
The Bottom Line
Depletion of the ozone layer by CFCs (Chlorofluorocarbons)
In the stratosphere
The Balance Sheet
· Are small solid particles and liquid droplets in the air, excluding cloud droplets and precipitation
· Are sometimes called particulates
· Have radii as small as 0.1 micrometer
· Fall so slowly they stay suspended in the atmosphere
· Are swept out by precipitation
· Have residence times of a few days to several weeks
· Reduce visibility
· Act as cloud nuclei
· Are related to air pollution and climate change
Also important in Chapter 1:
The thickness of the atmosphere, pp. 4-5
The composition of the atmosphere, pp. 5-11
Vertical structure of the atmosphere, pp. 13-17, and figures 1-9 and especially 1-10
Significant weather events, pp.3-4, and the special interest section on pp. 20-21
· Is energy of motion
· Includes the winds, radiation from the sun
· Can be transferred by conduction (direct contact of molecules) like holding a metal pin in a flame
· Can be transferred by convection (movement of groups of molecules) like rising motion in a pot of water on a stove
· Can be transferred by radiation (electromagnetic waves)
· Everything emits radiation.
· Thinking of electromagnetic energy as waves, each kind of radiation has its own wavelength.
· All radiation travels at the speed of light.
· Wavelengths are often measured in micrometers, millionths of a meter (or thousandths of a mm).
· A blackbody emits the maximum possible radiation at every wavelength.
· A graybody is a slightly imperfect blackbody. The earth’s surface and the sun are graybodies, and are often called blackbodies too.
· The atmosphere is neither a blackbody nor a graybody. The atmospheric gases are selective absorbers.
· Hotter bodies emit more energy than cooler ones.
· The amount of radiation emitted by an object is more than proportional to its temperature
· Intensity of radiation = a constant x T x T x T x T
· For graybodies, the blackbody radiation is multiplied by an emissivity, usually between 0.9 and 1.0 (the maximum value).
· The sun emits a much greater intensity of radiation than the earth.
· The radiation of a blackbody or graybody like the sun and the earth is not a single wavelength.
· Not all wavelengths are emitted in equal amounts.
· Wavelength of peak emissions = a constant / T
· Hotter objects radiate energy at shorter wavelengths than do cooler bodies.
· Hotter objects radiate a higher proportion of energy at shorter, more energetic wavelengths.
· Hotter bodies radiate more energy than do cooler bodies at all wavelengths.
· Solar radiation is mostly in wavelengths shorter than 4 micrometers, called shortwave radiation.
· About 46.5% of solar radiation is near infrared and thermal infrared.
· About 46.8% of solar radiation is visible light.
· About 6.7% of solar radiation is ultraviolet radiation.
· Radiation from the earth (and its atmosphere) is mainly in wavelengths longer than 4 micrometers.
· These longer wavelengths are called longwave radiation.
· Solar radiation is not lost on the way from the sun to the earth; it is spread out over a larger area.
· The inverse square law describes how solar radiation spreads out.
· Incoming solar radiation is called insolation.
· The earth rotates from west to east, in the same sense as its rotation around the sun.
· Seasons occur because the earth’s axis is tilted 23.5 degrees away from perpendicular to the earth’s path around the sun (the ecliptic plane).
· The solar angle at noon changes with the seasons and with latitude. The intensity of solar radiation is greatest where the sun is highest in the sky.
· Beam spreading is greatest where the sun is lowest in the sky.
· The length of daylight changes with the seasons. The total amount of solar radiation received is greater where daylight lasts longer, if all other factors are the same.
· Where the solar angle is low (sun close to the horizon), beam depletion also decreases the intensity of solar radiation.
Gases as selective absorbers of radiation
· Of the incoming short-wave radiation, the atmosphere absorbs 25%. This includes absorption of ultraviolet light by ozone in the stratosphere and absorption of near-infrared short-wave radiation in the troposphere by the greenhouse gases (mostly water vapor).
· Long-wave radiation emitted by the Earth’s surface is largely absorbed in the atmosphere. This energy absorption increases the temperature of the atmosphere. The atmosphere can then radiate more energy outward, both up and down.
· When the earth’s surface absorbs the long-wave radiation from the atmosphere, its temperature can increase. The earth then radiates more energy outward.
· This cycle of absorption and re-emission of radiation continues. Its result is a higher average temperature for both earth and atmosphere than would be possible without the greenhouse gases.
The atmospheric greenhouse effect
· Without the greenhouse gases, Earth’s surface would have an average temperature of -18º C (0º F).
· With the greenhouse gases, Earth’s surface has a mean temperature of 15º C (59º F).
· Without the greenhouse gases, the temperature of Earth would oscillate wildly between very high during the day and very low at night.
· If the amount of greenhouse gases in the atmosphere changes, Earth’s average temperature changes so that the amount of incoming solar radiation balances the amount of outgoing long-wave radiation. This is called the equilibrium temperature. The exact value is predicted by the Stefan-Boltzmann law.
· The range of wavelengths not readily absorbed by atmospheric cases, between 8 and 12 micrometers, is called the atmospheric window.
· Clouds readily absorb all wavelengths of long-wave radiation, even in the wavelengths of the atmospheric window.
Facts about the energy budget of the earth and atmosphere
· Earth, the atmosphere, and clouds together reflect and scatter 30% of the incoming short-wave solar radiation back to space. This 30% is called the planetary albedo.
· The earth gains more energy by absorbing radiation than it loses by radiating energy.
· The atmosphere loses more energy by radiating than it gains by absorbing radiation.
· Together, the earth and atmosphere radiate out to space the same amount of energy in long-wave radiation that they receive from the sun in short-wave radiation.
· Convection and conduction transfer sensible and latent heat from the earth to the atmosphere. This balances the energy budget for the earth and the energy budget for the atmosphere.
· The balance between incoming and outgoing radiation for the system made up of the earth and atmosphere is balanced only for the planet as a whole.
· Poleward of latitude 38° in both hemispheres, there is a net loss of energy because outgoing longwave radiation exceeds incoming shortwave radiation.
· Equatorward of latitude 38° in both hemispheres, there is a net gain of radiation, because incoming solar radiation exceeds outgoing longwave radiation.
· The energy surplus at low latitudes and energy deficit at high latitudes are balanced by horizontal movement of air and ocean water, a form of convection called advection, in winds and ocean currents.
· Ocean currents transport warm water poleward and cool water equatorward.
· Even more important, winds carry both sensible and latent heat poleward, and on average bring cooler air equatorward.
· Isotherms on a chart connect points of equal temperature.
· Temperatures decrease poleward in both hemispheres
· The latitudinal temperature gradient (change in temperature/distance) is greatest in the winter hemisphere.
· Temperatures over land are higher than temperatures over the oceans at the same latitude in summer.
· Temperatures over land are lower than temperatures over the oceans at the same latitude in winter.
· Seasonal variations in temperature over land are greater than over water.
· Latitude is the greatest influence on temperature.
· Land and water contrasts are also important influences on temperature.
· Water changes temperature much less readily than land.
· Radiation penetrates water more deeply than land.
· Evaporation over water requires energy that would otherwise increase the temperature.
· Convection in water distributes energy surpluses in the horizontal and the vertical.
· Ocean currents also influence the temperature of coastal cities.
· Higher altitudes usually are cooler than lower altitudes, if all other factors are the same.
· Evaporation occurs when water molecules break free from the surface of a liquid to become water vapor molecules. This process requires energy.
· Condensation occurs when water vapor molecules randomly collide with the liquid water surface and bond to the adjacent liquid water molecules. This process releases energy.
· Saturation occurs when the rate of evaporation equals the rate of condensation.
· If more water vapor is added to saturated air, water droplets or ice crystals form.
· Saturated air contains as much water vapor as possible.
· Vapor pressure is that part of the total atmospheric pressure due to water vapor. It depends on temperature and the density of water vapor molecules. Measured in millibars.
· There are several other measures of humidity, including absolute humidity, mixing ratio, relative humidity, and dew point.
· The vapor pressure for saturated air, called the saturation vapor pressure, varies with temperature.
· Saturation vapor pressure increases as temperature increases, and it decreases as temperature decreases.
Not covered on test #1
Carbon dioxide as it relates to plant growth, pages 9-10;
Depletion of the ozone layer, page 12;
Evolution of the atmosphere, pages 19-22.
The structure of the sun, pages 40-41.
Pages 69-end of chapter, Latitudinal variations, Global temperature distributions, Influences on temperature, Measurement of temperature, Atmospheric Optics.