Chapter 4 Heat Temperature and Circulation Temperature Scales

Chapter 4 Heat, Temperature, and Circulation

Temperature Scales • As temperature cools, atom and molecules would move slower. • Absolute Zero – temperature in which an objects emits no radiation and no thermal motion. – 0 K (No negative numbers) – -273. 15 o. C – -459. 67 o. F • Some atomic level activity still occurs

Temperature Scales • o. F o. C o 32 = 9/5 + • o. C = 5/9 (o. F - 32 o) o • K = 5/9 ( F + 459. 67) o • K = C + 273. 15

Heat Units • Calorie (cal) – amount of heat needed to raise the temperature of 1 gram of water by 1 Celsius degree – This calorie has nothing to do with food calories • British Thermal Unit (Btu) – amount of heat needed to raise the temperature of 1 pound of water by 1 Fahrenheit degree • Joule (J) – most common form of measuring heat • 1 cal = 4. 1868 J • 1 Btu = 252 cal = 1055 J

Measuring Air Temperature • Thermometer – device used to measure variations in temperature • Liquid in Glass – Invented in 1593 by Galileo – Filled with mercury (freezes at – 38 o. F) or alcohol (freezes at -179 o. F) • Bimetallic – Two metals bonded together (brass and iron) that bend when heated or cooled – Rigged to a pen and drum that records continuous temperature - thermograph

Measuring Air Temperature • Electrical Conductor – variations in electrical resistance calibrated in terms of temperature – Used in radiosondes – Replacing liquid in glass thermometers in NWS • Cricket chirps: temperature must be above 54 o. F – # of chirps in 8 seconds + 4 = o. C • Methods for accurate measurements – Ventilation – Shielded from precipitation, direct sunlight, night sky – Located away from obstacles such as trees, buildings

Heat Transfer • Temperature Gradient – a change in temperature with distance • Second Law of Thermodynamics (Entropy) – all systems tend towards disorder trying to eliminate gradients – Heat flows from higher temperature to lower temperature to erase the gradient – Larger the gradient the faster the rate of change • Types – Conduction, Convection, Radiation

Radiation • Form of energy and energy transfer • Can travel through a vacuum • Principal means of EA system gaining heat from the sun and heat escaping to space • Radiational Heating – absorption > emission • Radiational Cooling – absorption < emission • Radiational Equilibrium - absorption = emission (blackbody) • In equilibrium temperature is constant, though different parts may be different temperatures

Convection • Convection – transport of heat within a fluid due to the motions of the fluid itself – Only occurs in liquids and gases • In the atmosphere, it is caused by differences in air density – Cold dry air sinks because it is more dense – Warm moist air rises • This air expands, cools, and sinks again • Ex) Low pressure system

Conduction • Conduction – transfer of kinetic energy (heat) through collisions of molecules • Heat Conductivity – ratio of the rate of heat transport to a temperature gradient – Solids are best conductors, gases are worst – Poor conductors are good insulators (still air)

Thermal Response • Specific Heat – the amount of heat needed to raise 1 gram of a substance 1 degree Celsius (a calorie) • Q = mc(ΔT) – – Q: change in heat (calories, Joules) m: mass of object (grams) c: specific heat capacity (calories/gram o. C) ΔT: change in temperature (o. C) • A higher value of “c” indicates a greater ability to store heat and resist temperature change • Thermal Inertia – resistance to temperature change

Thermal Response • Because water retains heat better than land, areas near the coast have less temperature variation throughout the year

Sea Breeze Effect

Heat Imbalance (Surface v. Atmosphere) • Earth’s surface undergoes net radiational heating • Earth’s atmosphere undergoes net radiational cooling • In response to this unbalance, heat is transferred to the atmosphere from the surface

Heat Imbalance (Tropics v. Poles)

Heat Imbalance (Tropics v. Poles) • Tropical Areas: incoming solar radiation is greater than outgoing IR radiation • Polar Areas: incoming solar radiation is less than outgoing IR radiation • Global Radiative Equilibrium: surplus of solar radiation = deficit of IR radiation • Excess heat in tropics is transported to higher latitudes by air masses

Response to Heat Imbalance: Weather • Heat imbalances create temperature gradients – Between surface and troposphere – Between tropics and polar latitudes • Heat is transported by conduction, convection, clouds, air masses, storms – Circulation of the atmosphere • Circulation brings about changes in the state of the atmosphere – WEATHER

Temperature Variations • • Time and Day of year: solar intensity, angle Cloud Cover Surface Characteristics (albedo) Temperature is warmer when – – – It is daylight Under clear skies during the day Under cloudy skies during the night When the ground is not snow covered When the ground is dry (2012)

Air Mass Advection • Movement of an air mass from one place to another • Warm Air Advection (WAA) – Movement of warm air • Cold Air Advection (CAA) – Movement of cold air • Advection occurs when isobars and isotherms are NOT parallel

Degree Days • Based on 65 o. F • Approximations of residential fuel demands for heating and cooling • Heating Degree Day – HDD = 65 o. F – Average Daily Temperature • Cooling Degree Day – CDD = Average Daily Temperature - 65 o. F

Accumulated Degree Days for Corn Growing Degree Days

Wind 0. 16 Chill • WC = 35. 74 + 0. 6215 T – 35. 75(V – T = Temperature in Fahrenheit – V = wind velocity in miles per hour ) + 0. 4275 T(V 0. 16)