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Basic Properties of the Atmosphere

Basic Properties of the Atmosphere. The Atmosphere: Structure and Temperature. Meteorology : the study of the physics, chemistry, and dynamics (movement) of the Earth’s atmosphere Atmosphere : Envelope of gases bound to the Earth by gravity

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Basic Properties of the Atmosphere

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  1. Basic Properties of the Atmosphere

  2. The Atmosphere: Structure and Temperature • Meteorology: the study of the physics, chemistry, and dynamics (movement) of the Earth’s atmosphere • Atmosphere: Envelope of gases bound to the Earth by gravity • Weather: State of the atmosphere at a given time and place; constantly changing • Weather is described by variables such as: • -- Temperature -- Wind Speed and Direction • -- Pressure -- Precipitation • -- Cloud Cover

  3. The Atmosphere: Structure and Temperature • Weather is constantly changing, and it refers to the state of the atmosphere at any given time and place. • Climate, however, is based on observations of weather that have been collected over many years. Climate helps describe a place or region.

  4. Climatology: study of climate types and patterns and the causes of those patternsClimate: sum of all statistical weather info that helps describe a place or regionSlowly - varyingAverages (monthly, yearly)Ranges (largest value - smallest value)Extremes (maximum, minimum) Composition of the Atmosphere

  5. Weather or Climate??? • The average high temperature for the month of July in Phoenix is 111oF. • Cumulus clouds presently cover the entire sky. • Snow is falling at a rate of 1 inch per hour. • The summers here are warm and humid. • At 3:00 p.m, winds were blowing from the NW at 10 mph. • Total precipitation at O’Hare Airport for 2003 was 32.02 inches, which is 4.25 inches below normal.

  6. Origin of the atmosphere • The original atmosphere • Probably made up of hydrogen and helium. • These are fairly common in the universe. • Original atmosphere stripped away by the solar wind • H and He are very light • Hydrogen and helium have the smallest atoms by mass. • The early earth was not protected by a magnetic field. • Thus the current atmosphere is considered a secondary atmosphere

  7. The secondary atmosphere • Formed from degassing of volcanoes • Gasses emitted probably similar to the gasses emitted by volcanoes today. • H2O (water), 50-60% • CO2 (carbon dioxide), 24% • SO2 (sulfur dioxide), 13% • CO (carbon monoxide), • S2 (sulfur), • Cl2 (chlorine), • N2 (nitrogen), • H2 (hydrogen), • NH3 (ammonia) and • CH4 (methane)

  8. Modern atmosphere Nitrogen (N2)- 78%, Oxygen (O2)- 21%, Carbon Dioxide (CO2) 0.03 %, Where did all the oxygen come from?

  9. Modern atmosphere • Life changes the atmosphere • With the evolution of life the first cellular organisms began to use the gasses in the early atmosphere NH3 – ammonia, CH4 – methane, H2O – water for energy. Photosynthetic organisms evolve. (cyanobacteria) These organisms use CO2 and produce oxygen (O2) as a waste product.

  10. Modern atmosphere • Where did the O2 come from? • Produced by photosynthetic life. • Where did the CO2 go? • Dissolves in water in the oceans • Used by life by photosynthesis and buried when plants and micro-organisms die. • The source of coal and oil

  11. Atmosphere Characteristics Permanent gases: Variable gases: (together 99.96%) (N) Nitrogen 78% (CO2) Carbon dioxide (O) Oxygen 21% (O3) Ozone (Ar) Argon ~ .9% (H2O) Water vapor - Neon (Ne)(0.001818%) Helium (He)(0.000524%) Methane (CH4)(0.0001745%) Krypton (Kr)(0.000114%) Hydrogen (H2) varies from 4% to less than 1% Green House Gases

  12. Atmosphere Characteristics  Variable Components • Water vapor is the source of all clouds and precipitation. Like carbon dioxide, water vapor absorbs heat given off by Earth. It also absorbs some solar energy. • Ozone is a form of oxygen that combines three oxygen atoms into each molecule (O3). • If ozone did not filter most UV radiation and all of the sun’s UV rays reached the surface of Earth, our planet would be uninhabitable for many living organisms.

  13. Atmospheric Structure  The atmosphere rapidly thins as you travel away from Earth until there are too few gas molecules to detect. • Pressure Changes • Atmospheric pressure is simply the weight of the air above.

  14.  Pressure Changes

  15.  Pressure Changes

  16. Observing the Atmosphere • Air Pressure: force per area exerted by the mass of air above a point • Measured in: • Inches of mercury (in. Hg) • Millibars (mb) • Average sea-level pressure = 1013.25 mb or 29.92 in. Hg • Air pressure is Measured using a barometer

  17. Mercury Barometer Barometer - apparatus used to measure pressure;  is derived from the Greek "baros" meaning "weight"  Aneroid Barometers: (without liquid)

  18. Air Pressure • By lucky coincidence, earth’s atmospheric pressure is approximately neat round numbers in metric terms • 14.7 pounds per square inch (1 kg/cm2) • Pressure of ten meters of water • Approximately one bar or 100 kPa • Weather reports use millibars (mb) • One mb = pressure of one cm water

  19. 120 110 100 THERMOSPHERE 90 Mesopause 80 70 MESOPHERE 60 Height above ground (kilometers) 50 Stratopause 40 30 STRATOSPHERE 20 Tropopause 10 TROPOSPHERE 0 -120 -100 -80 -60 -40 -20 0 20 40 60 COLDER WARMER Atmospheric Pressure vs. Altitude The atmosphere is divided into layers based on temperature.

  20. Structure of the Atmosphere • Defined by Temperature Profiles • Troposphere • Where Weather Happens • Stratosphere • Ozone Layer • Mesosphere • Thermosphere • Ionosphere

  21. Atmosphere Characteristics  Temperature Changes • The atmosphere can be divided vertically into four layers based on temperature. • The troposphere is the bottom layer of the atmosphere where temperature decreases with an increase in altitude. • The stratosphere is the layer of the atmosphere where temperature remains constant to a height of about 20 kilometers. It then begins a gradual increase until the stratopause.

  22. Atmosphere Characteristics  Temperature Changes • The mesosphere is the layer of the atmosphere immediately above the stratosphere and is characterized by decreasing temperatures with height. • The thermosphere is the region of the atmosphere immediately above the mesosphere and is characterized by increasing temperatures due to the absorption of very short-wave solar energy by oxygen.

  23. Thermal Structure of the Atmosphere

  24. Heating the Atmosphere • Heat is the energy transferred from one object to another because of a difference in the objects’ temperature.  Temperature is a measure of the average kinetic energy of the individual atoms or molecules in a substance.

  25. Observing the Atmosphere • Temperature: measure of the motion of the molecules in a substance • Hot air: molecules moving more quickly • Cold air: molecules moving less quickly • Measured using a thermometer • Always measured in shady conditions • Units: oC, oF

  26. Heat and Temperature • Temperature: Average energy of molecules or atoms in a material • Heat: Total energy of molecules or atoms in a material • Can have large amount of heat but low temperatures • Can have high temperatures but little heat

  27. Heat and Temperature • The Arctic Ocean has a large amount of heat (because of large mass) even though the temperature is low. • Air in an oven at 500 F has high temperature but little heat. • However, touch anything solid in the oven, and you’ll get burned. Same temperature, much larger amount of heat.

  28. HEAT & TEMPERATURE • Heat is a measure of energy. • Matter is composed of atoms & molecules that are constantly vibrating and • Heat = total kinetic energy of atoms & molecules • By contrast, Temperature is a measure of intensity. • Temperature = average kinetic energy of individual atoms and molecules.  • Heat and Temperature are of course closely related: • Add heat -> molecules move faster -> temperature rises Remove heat -> molecules move slower -> temperature falls.

  29. Temperature Scales • Fahrenheit • Water Freezes at 32 F • Water Boils at 212 F • Centigrade or Celsius • Water Freezes at 0 C • Water Boils at 100 C • Two scales exactly equal at -40

  30. Converting C to F – In Your Head • Double the Centigrade • Subtract the first Digit • Add 32 °C = (°F – 32) / 1.8

  31. Converting F to C – In Your Head • Subtract 32 • Add the first Digit • Divide by two °F = 1.8 (°C) + 32

  32. Absolute Temperature • Once atoms stop moving, that’s as cold as it can get • Absolute Zero = -273 C = -459 F • Kelvin scale uses Celsius degrees and starts at absolute zero • Most formulas involving temperature use the Kelvin Scale

  33. Heating the Atmosphere  Three mechanisms of energy transfer as heat are conduction, convection, and radiation.  Conduction • Conduction is the transfer of heat through matter by molecular activity.  Convection • Convection is the transfer of heat by mass movement or circulation within a substance.

  34. Heating the Atmosphere  Electromagnetic Waves • The sun emits light and heat as well as the ultraviolet rays that cause a suntan. These forms of energy are only part of a large array of energy emitted by the sun, called the electromagnetic spectrum.

  35. Visible Light Consists of an Array of Colors

  36. Heating the Atmosphere  Radiation • Radiation is the transfer of energy (heat) through space by electromagnetic waves that travel out in all directions. • Unlike conduction and convection, which need material to travel through, radiant energy can travel through the vacuum of space.

  37. Energy Transfer as Heat VOCABULARY radiation conduction convection temperature heat troposphere stratosphere ozone mesosphere thermosphere ionosphere insolation

  38. Heating the Atmosphere  Radiation • All objects, at any temperature, emit radiant energy. • Hotter objects radiate more total energy per unit area than colder objects do. • The hottest radiating bodies produce the shortest wavelengths of maximum radiation. • Objects that are good absorbers of radiation are good emitters as well.

  39. Heating the Atmosphere  When radiation strikes an object, there usually are three different results. 1. Some energy is absorbed by the object. 2. Substances such as water and air are transparent to certain wavelengths of radiation. 3. Some radiation may bounce off the object without being absorbed or transmitted.

  40. Heating the Atmosphere  Reflection and Scattering • Reflection occurs when light bounces off an object. Reflection radiation has the same intensity as incident radiation. • Scattering produces a larger number of weaker rays that travel in different directions.

  41. Heating the Atmosphere  Absorption • About 50 percent of the solar energy that strikes the top of the atmosphere reaches Earth’s surface and is absorbed. • The greenhouse effect is the heating of Earth’s surface and atmosphere from solar radiation being absorbed and emitted by the atmosphere, mainly by water vapor and carbon dioxide.

  42. SOLAR RADIATION 6 units radiate to space from Earth’s surface 30 units reflected or scattered back to space A total of 64 units radiated back into space via the atmosphere Atmosphere absorbs 19 units 15 units radiate from surface to atmosphere Evaporation transfers 23 units to atmosphere Earth’s surface absorbs 51 units Conduction and convection transfer 7 units to atmosphere 100 units of Insolation Earth’s heat budget represents the flow of energy into and out of Earth’s atmosphere. An imbalance in Earth’s heat budget changes Earth’s mean temperature.

  43. SOLAR RADIATION About 50% of the incoming solar radiation is absorbed by the Earth’s surface. Most of the molecules in the Earth’s atmosphere do not absorb visible or shortwave radiation. The Earth’s surface warms, and emits energy in the form of infrared or longwave radiation, which is invisible to the human eye. Certain molecules in the atmosphere, called greenhouse gases, do absorb the Earth’s infrared radiation. This absorption warms the atmosphere. Also, the greenhouse gas molecules emit their own infrared radiation, which is absorbed by other molecules, and the atmosphere warms even more!

  44. Local Temperature Variations Equator The angle of sunlight varies with latitude. Atmosphere VOCABULARY The intensity of insolation depends upon the angle at which sunlight strikes Earth’s surface. The intensity is greatest at low latitudes, during the summer, and around noon. isotherm A line drawn on a weather map through places having the same atmospheric temperature at a given time.

  45. Tilt of Earth’s Axis Insolation: The solar (energy) radiation that reaches Earth. reaches Earth. **The Axial Tilt of the Earth is the cause of the seasons.

  46. Tilt of Earth’s Axis Altitude of sun affects amount of energy received at surface because lower angle -> more spread out and less intense radiation (as for flashlight beam). lower angle -> more of atmosphere to pass through, and hence more chance to be absorbed or reflected (can look at sun at sunset).

  47. New Orleans New Orleans SUN’S RAYS Equator Equator June 21 Dec. 21 During the summer, the Northern Hemisphere is tilted towards the Sun. Here, locations receive the Sun’s most direct rays, and have longer periods of daylight hours. During the winter, the Northern Hemisphere is tilted away from the Sun. Periods of daylight are shorter, and the Sun’s rays are less direct.

  48. Solstices and Equinoxes During the vernal (spring) and autumnal (fall) equinoxes, neither hemisphere is tilted towards or away from the Sun. On these dates, every location on Earth receives 12 hours of daylight and 12 hours of darkness.

  49. Atmosphere Characteristics  Solstices and Equinoxes • The summer solstice is the solstice that occurs on June 21 or 22 in the Northern Hemisphere and is the “official” first day of summer. • The winter solstice is the solstice that occurs on December 21 or 22 in the Northern Hemisphere and is the “official” first day of winter.

  50. Atmosphere Characteristics  Solstices and Equinoxes • The autumnal equinox is the equinox that occurs on September 22 or 23 in the Northern Hemisphere. • The spring equinox is the equinox that occurs on March 21 or 22 in the Northern Hemisphere.

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