AOSC Lesson 2

Temperature Scales Temperature scales are defined by upper and lower calibration points (fixed points) In the Fahrenheit temperature scale the lower fixed point of 0°F is defined as the temperature of a mixture of salt and ice. Dr. Fahrenheit was a physician, and he defined the upper fixed point, 100°F, as the average temperature of his (sick?) patients. In the Centigrade (Celsius) scale, the lower fixed point, 0°C, is defined as the temperature of the melting point of ice, while the upper fixed point, 100°C, is defined as the boiling point of water. The Kelvin scale is a scientific scale. Here the lowest fixed point 0°K is defined as the theoretically lowest temperature that can be reached. On this scale the melting point of ice is about 273°K. One degree K = one degree C.

Fig. 2-1, p. 29

Table 2-1, p. 30 Specific Heat

How is energy transferred in the atmosphere? Tornados, Hurricanes, Severe Storms all require a large energy source. All of this energy comes from the Sun. So, how is this energy transferred within the atmosphere? Five major processes, (1) conduction (2) convection (3) advection (4) transfer of radiation (5) latent heat of vaporization of water

Fig. 2-2, p. 30 CONDUCTION

Fig. 2-3, p. 31 CONVECTION

Fig. 2-4, p. 31 ADVECTION

Transfer of Energy in the Atmosphere CONDUCTION TRANSFER OF ENERGY THROUGH MATTER AIR IS A POOR CONDUCTOR ONLY IMPORTANT AT THE EARTH'S SURFACE CONVECTION TRANSFER OF ENERGY BY MOVEMENT OF MASS CAN ONLY TAKE PLACE IN LIQUIDS – IN SCIENTIFIC TERMS AIR IS A LIQUID. ENERGY ACQUIRED AT SURFACE OF EARTH IS TRANSPORTED UPWARD BY CONVECTIVE FLOW CONVECTION ON A GLOBAL SCALE CREATES WORLDWIDE ATMOSPHERIC CIRCULATION ADVECTION HORIZONTAL MOVEMENT OF AIR

Fig. 2-5, p. 33 PHASE CHANGES OF WATER

Latent heat – Changing the Phase of Water LATENT HEAT IS THE HEAT ABSORBED OR RELEASED BY UNIT MASS OF WATER WHEN IT CHANGES PHASE. –LATENT HEAT OF MELTING / FUSION –LATENT OF VAPORIZATION / CONDENSATION –LATENT HEAT OF SUBLIMATION / DEPOSITION THIS GIVES US ANOTHER WAY OF TRANSFERRING ENERGY IN THE ATMOSPHERE THE OCEANS ABSORB SOLAR ENERGY TO EVAPORATE WATER VAPOR. THE WATER VAPOR IS TRANSPORTED BY WINDS ETC WHEN THE WATER VAPOR CONDENSES TO FORM CLOUDS THE LATENT HEAT IS RELEASED. THE LATENT HEAT RELEASED IS THE SOURCE OF ENERGY THAT DRIVES SEVERE WEATHER, E.G. HURRICANES.

Fig. 2-6, p. 34 Radiation Energy is transferred to the Earth from the sum by electromagnetic waves. Other examples of electromagnetic waves are microwave and radio waves. Each wave is characterized by a wavelength(the distance between successive peaks) and a frequency ( the number of peaks that pass by per second)

Fig. 2-7, p. 34 ELECTROMAGNETIC SPECTRUM

Wien’s Displacement Law: Stephan-Boltzmann Law: Laws of Radiation

Fig All things emit thermal radiation. This is a picture of a person holding a match. It was taken with a camera sensitive to infrared radiation.

Fig. 2-8, p. 36 Note that the peak of the Earth’s radiation occurs at 10  m while that for then sun is at 0.5  m, a ratio of 20. The ratio of the temperatures is 1/20. (Wien’s Displacement Law)

SEVERAL QUESTIONS WHY DOES THE EARTH HAVE SEASONS? WHY ARE THE POLES COLD YET THE EQUATOR IS HOT? WHY IS DAYLIGHT LONGER IN THE SUMMER THAN IN THE WINTER?

Fig. 2-14, p. 43

Fig. 2-11, p. 41

Fig. 2-12, p. 42 HEATING OF THE EARTH’S SURFACE DEPENDS ON THE AMOUNT OF SOLAR RADIATION PER UNIT AREA. SAME AMOUNT OF RADIATION IS DISTRIBUTED OVER A LARGER AREA IN A THAN IN B. RADIATION PER UNIT AREA IS LESS IN A THAN IN B. LESS HEATING IN A THAN IN B.

Fig. 2.15

Fig. 2-15, p. 43

Fig. 2-16, p. 44

Table 2-2, p. 44

Fig. 2-17, p. 45

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The Earth’s Orientation EARTH'S AXIS IS NOT PERPENDICULAR TO THE PLANE OF ITS ORBIT AROUND THE SUN. IT IS TILTED 23.5 DEGREES FROM THE PERPENDICULAR INCLINATION OF THE AXIS. WITHOUT THIS INCLINATION WE WOULD HAVE NO SEASONS. THIS CHANGES THE SOLAR ZENITH ANGLE OF THE SUN, AND THE AREA COVERED BY A BEAM OF SUNLIGHT AREA COVERED BY BEAM IS PROPORTIONAL TO 1/COS OF THE SOLAR ZENITH ANGLE IN COLLEGE PARK, SOLAR ZENITH ANGLE OF THE SUN IS 67 DEGREES ON DEC 22, AND 19 DEGREES ON JUNE 22. THE RATIO OF 1/COS OF THE ANGLES IS ABOUT 2. TWICE AS MUCH ENERGY FALLS ON UNIT AREA AT THE GROUND IN SUMMER THAN IN WINTER. THE LENGTH OF THE DAY ALSO VARIES WITH SEASON – ALSO A RESULT OF THE INCLINATION OF THE EARTH.

Fig. 2-19, p. 49

Incoming Solar Radiation 25% PENETRATES DIRECTLY TO EARTH'S SURFACE. 26% SCATTERED BY ATMOSPHERE BUT THEN REACHES THE SURFACE. TOTAL OF 51% REACHES SURFACE. 31% REFLECTED BACK TO SPACE BY CLOUDS, ATMOSPHERIC SCATTERING, AND REFLECTIVE SURFACES, E.G. SNOW AND ICE. 19% ABSORBED BY CLOUDS AND ATMOSPHERIC GASES

Absorption GASES ARE EXCELLENT ABSORBERS. WHEN RADIATION IS ABSORBED, ENERGY IS CONVERTED INTO INTERNAL MOLECULAR MOTION - RISE OF TEMPERATURE. SIGNIFICANT ABSORBERS ARE: OXYGEN AND OZONE WATER VAPOR

Reflection THE FRACTION OF ENERGY THAT IS REFLECTED BY A SURFACE IS CALLED ITS ALBEDO. ALBEDO OF THE EARTH AS A WHOLE IS 30%. ALBEDO OF FRESH SNOW IS 80-85% THICK CLOUD - 70 TO 80% WATER - DEPENDS ON ELEVATION OF THE SUN, FROM 50 TO 80% NEAR HORIZON, 3-5% AT 90 DEGREES. SOIL- 10%

Scattering PRODUCES DIFFUSE LIGHT SHORTER WAVELENGTHS (BLUE AND VIOLET) ARE SCATTERED MORE EFFECTIVELY THAN LONGER WAVELENGTHS (RED AND ORANGE). HENCE SKY APPEARS BLUE WHEN VIEWED AT NOON. AT SUNSET PREFERENTIALLY SCATTERING DEPLETES AMOUNT OF BLUE LIGHT IN DIRECT BEAM - BEAM APPEARS REDDISH. SCATTERING MORE EFFICIENT AS PARTICLE GETS LARGER - AEROSOLS OR DUST.

Fig. 2-20, p. 50

Latitudinal Heat Balance FOR THE GLOBE AS A WHOLE, THE AMOUNT OF INCOMING SOLAR RADIATION IS EQUAL TO THE OUTGOING TERRESTRIAL RADIATION. HOWEVER THIS STATEMENT DOES NOT HOLD TRUE AT ANY GIVEN LATITUDE IN GENERAL THERE IS A SURPLUS OF ENERGY AT THE EQUATOR - MORE RADIATION COMES IN THAN GOES OUT THERE IS ALSO A DEFICIT OF ENERGY AT THE POLES – MORE RADIATION GOES OUT THAN COMES IN. WHY THEN DO THE POLES NOT GET COLDER AND THE EQUATOR HOTTER? BECAUSE HEAT IS TRANSPORTED FROM THE EQUATOR TO THE POLES BY OCEAN CURRENTS (E.G. THE GULF STREAM) AND BY THE ATMOSPHERE.

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Simple Greenhouse Model

Fig. 3-2, p. 55

Greenhouse Effect

The Blue Marble