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THE ENERGY BALANCE AT SURFACE

THE ENERGY BALANCE AT SURFACE. 1 st LAW OF THERMODYNAMICS (CONSERVATION OF ENERGY): Energy only changes from one form to another. It cannot be created or destroyed. Net Radiation + Sensible Heat + Latent Heat + Ground Heating = 0. Read pages 49, 56-57 Book. SENSIBLE AND LATENT HEAT.

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THE ENERGY BALANCE AT SURFACE

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  1. THE ENERGY BALANCE AT SURFACE 1st LAW OF THERMODYNAMICS (CONSERVATION OF ENERGY): Energy only changes from one form to another. It cannot be created or destroyed. Net Radiation + Sensible Heat + Latent Heat + Ground Heating = 0 Read pages 49, 56-57 Book

  2. SENSIBLE AND LATENT HEAT STATES OF MATTER Gas: The particles move rapidly; there are larger spaces between them Liquid: The particles move less rapidly; they are closer Solid: The particles move very little and are arranged in a tight pattern Gas Liquid Solid

  3. SENSIBLE AND LATENT HEAT HEAT TRANSFER: • Radiation: electromagnetic waves transport energy trough space (e.g. sun radiation) • Conduction: the transfer of energy trough matter from particle to particle. • Convection: the transfer of heat by mass motion of a fluid (water, air) when the heated fluid is caused to move away from the source of heat (the heated fluid is less dense and rises)

  4. SENSIBLE HEAT: • Heat sensed by touching or feeling (measured by a thermometer) • Sensible heat transfer (Ex: conduction, convection) • LATENT HEAT: • Hidden heat. It’s stored in the form of a molecular motion when a substance change from solid to liquid, liquid to gas, or solid to gas • Latent heat transfer: when water evaporates from a moist surface or water surface it removes the heat stored in the change of state (transference of heat from surface to atmosphere) • cooling surface

  5. SENSIBLE HEAT LATENT HEAT

  6. SURFACE AND AIR TEMPERATURE • TEMPERATURE: • Temperature is the measure of level of sensible heat of matter (gaseous, liquid, solid) • SURFACE TEMPERATURE: • Temperature in a surface is determined by the balance among various energy flows: • Net radiation (positive at day, negative at night) • Sensible heat transfer • Conduction: from warm to cold trough direct contact • (ex: heat into soils) • Convection: fluid is heated by warm surface, expand, rises (upward flow) • Latent heat transfer:when water evaporates at a surface, it removes heat stored (cooling surface). When condenses at surface, latent heat is released (warming surface)

  7. THE AIR TEMPERATURE (CHAPTER 3 BOOK) • Temperature observed at short distance above surface (1.2m or 4 feet) • Air temperature and surface temperature can be different, but air temperatures tend to follow surface temperatures (because of heat flows) • Weather information uses air temperature

  8. AIR TEMPERATURE MEASUREMENT • In US is widely measured using Farenheit • The Celsius scale is the international standard • The World Meteorological Organization (WMO) is a specialized agency of United Nations. One of its purposes is to promote standardization of meteorological observations • http://www.worldweather.org/ • Instrument used: • Thermometer • liquid-filled (expands when liquid is heated, contracts when is cooled) • thermistor (change of electrical resistance with temperature)

  9. Not always temperature at same latitudes are similar, for example: Baltimore (Midlatitude) Mongolia (Midlatitude) Min: 6.0 F Max: 60.0 F Min: 45.0 F Max: 65.0 F

  10. TEMPERATURE RANGE Daily: Tmax- Tmin Annual: Difference between the lowest and highest monthly mean temperatures

  11. THE AIR TEMPERATURE • The factors that influence air temperature are: • Insolation • 2. Latitude • 3. Surface type (urban, moist soil, forest, deserts) • 4. Coastal vs interior location: • Narrower range of air temperatures in coast (water heats and cools more slowly than land) • 5. Elevation

  12. S S E E ANNUAL CYCLE OF MAXIMUM AIR TEMPERATURE (SOUTHERN HEMISPHERE) In-class Exercise

  13. URBAN-RURAL DIFFERENCES RURAL: moist soil evaporation cooler surface vegetation transpiration URBAN: dry surface insolation warmer surface asphalt and roofing (dark surfaces) more absorption (twice the vegetation) warmer surface

  14. LAND AND WATER CONTRASTS • The range of temperature is lower in water • Continental air temperature isotherms shift over a much wider latitude range from summer to winter than oceanic air temperature isotherms.

  15. LAND AND WATER CONTRASTS • Reasons: • 1. Penetration vs no penetration of radiation • 2. Water heats and cools slowly than land • 3. Mixing (warm and cool water) vs no mixing • 4. More evaporation vs less evaporation 4. Less evaporation 4. More evaporation • No penetration • Land heats quickly 1. penetration 3. No mixing 3.mixing 2. Water heats slowly

  16. HIGH-MOUNTAIN ENVIRONMENTS

  17. DAILY CYCLE OF AIR TEMPERATURE • Factors: Earth’s rotation on its axis, latitude, urban/rural, elevation • During day: net radiation is positive • During night: is negative surface gains heat surface loses heat Location at 45°N Why minimum temperature takes place in early morning and not during the night? In-class Exercise

  18. During night: NEGATIVE net radiation heat flows from ground surface surface air layer warms a little bit, but remains with low temperatures Ground surface is cooled Surface air layer is cooled Lower temp Lower temp… Until net radiation is POSITIVE

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