1. AMS Weather Studies Introduction to Atmospheric Science, 5 th Edition Chapter 4 Heat, Temperature, & Atmospheric Circulation © AMS

2.  What are the causes and consequences of heat transfer within the Earth-atmosphere system?  This chapter covers:  Distinguishing temperature and heat  Heat transfer processes  Thermal response and specific heat  Heat imbalances  How does heat affect atmospheric circulation? © AMS2 Driving Question

3. Case-in-Point Extreme Heat of Death Valley, CA © AMS3  Death Valley – Hottest and driest place in North America  134°F in 1913  2nd highest temperature ever recorded on Earth  Summer 1996  40 successive days over 120°F  105 successive days over 110°F  Causes:  Topographic setting  Atmospheric circulation  Intense solar radiation Cooperative Weather observing station at Furnace Creek Ranch

4. © AMS4  All matter is composed of molecules or particles in continual vibrational, rotational, and/or translational motion.  Energy represented by this motion is called kinetic energy.  Temperature  Directly proportional to the average kinetic energy of atoms or molecules composing a substance  Internal energy  Encompasses all the energy in a substance  Includes kinetic energy  Includes potential energy, arising from forces between atoms/molecules  Heat is energy in transit  When two substances are brought together with different kinetic energy, energy is always transferred from warmer object to colder Distinguishing Temperature & Heat

5. © AMS5  Temperature Scales  Absolute zero  Temperature at which theoretically all molecular motion ceases  No electromagnetic radiation is emitted  Absolute zero = -459.67°F = 273.15°C = 0 K Distinguishing Temperature & Heat

6. © AMS6  Temperature scales measure degree of hotness or coldness  Calorie  Amount of heat required to raise temperature of 1 gram of water 1 Celsius degree  Different from “food” calorie, which is actually 1 kilocalorie  Joule  More common in meteorology today  1 calorie = 4.1868 joules  British Thermal Units (BTU)  Amount of energy required to raise 1 pound of water 1 Fahrenheit degree  1 BTU = 252 cal = 1055 J Distinguishing Temperature & Heat

7. © AMS 7  Thermometer  Liquid-in-glass thermometer  Uses mercury or alcohol  Bimetallic thermometer  Two strips of metal with different expansion/contraction rates  Electrical resistance thermometer  Thermograph  Measures and records temperature Bilmetallic thermometer The change of temperature during the passage of a cold front as determined by an electronic thermometer. Distinguishing Temperature & Heat Liquid-in-glass thermometer

8. © AMS8  Shielding temperature sensors  Important properties  Accuracy  Response time  Location is important  Ventilated  Shielded from weather Enclosure for the NWS electronic temperature sensor Distinguishing Temperature & Heat

9. © AMS9  Temperature gradient  Change in temperature over distance  Example: the hot equator and cold poles  Heat flows in response to a temperature gradient  This is the 2 nd law of thermodynamics  Heat flows toward lower temperature so as to eliminate the gradient  Heat flows/transfers in the atmosphere  Radiation  Conduction  Convection  Latent heat – phase changes in water Heat Transfer Processes

10. © AMS10 Heat Transfer Processes  Radiation  Both a form of energy and a means of energy transfer  Occurs even in a vacuum, such as space  Absorption of radiation by an object causes the temperature of object to rise  Converts electromagnetic energy to heat  Radiational heating  Absorption at greater rate than emission  Radiational cooling  Emission at greater rate than absorption

11. © AMS11  Conduction  Transfer of kinetic energy of atoms or molecules by collision between neighboring atoms or molecules  Heat conductivity  Rate of heat transport across an area to a temperature gradient  Some materials have a higher heat conductivity than others  Solids (metal) are better conductors than liquids  Liquids are better than gases (air)  Conductivity impaired by trapped air  Examples: fiberglass insulation, thick layer of fresh snow Heat Transfer Processes

12. © AMS12 A thick layer of snow is a good insulator because of air trapped between individual snowflakes. As snow settles, the snow cover’s insulating property diminishes. Heat Transfer Processes

13. © AMS13  Convection  Consequence of differences in air density  Transport of heat within a substance via movement of substance itself  Substance must liquid or gas  Very important process for transferring heat in atmosphere  The convection cycle  Ascending warm air expands, cools and eventually sinks back to ground Heat Transfer Processes

14.  Latent heating  Movement of heat from one location to another due to phase changes of water  Example: evaporation of water, movement of vapor by winds, condensation elsewhere © AMS14 Heat Transfer Processes

15.  Temperature change caused by input/output of a quantity of heat varies among substances  Specific heat  The amount of heat required to raise 1 gram of a substance 1 Celsius degree Thermal Response and Specific Heat © AMS15 The contrast in specific heat is one reason why the sand is hotter than the water.

16. © AMS16  Thermal inertia  Resistance to a change in temperature  Large body of water exhibits greater resistance to temperature change than land because of difference in specific heat  Maritime climate  Immediately downwind of the ocean experience much less annual temperature change  Continental climate  Locations well inland experience greater annual temperature change Thermal Response and Specific Heat San Francisco, CA, has a maritime climate while St. Louis, MO, has a continental climate.

17. © AMS17 Heat Imbalance: Atmosphere vs. Earth’s Surface  At Earth’s surface  Absorption of solar radiation is greater than emission of IR  In atmosphere  Emission of IR radiation to space is greater than absorption of solar radiation  Therefore,  Earth’s surface has net radiational heating  Atmosphere has net radiational cooling.  So, Earth’s surface transfers heat to the atmosphere, making up difference

18. © AMS18 Heat Imbalance: Atmosphere vs. Earth’s Surface

19. © AMS19

20. © AMS20 Heat Imbalance: Atmosphere vs. Earth’s Surface  Latent Heating  Some absorbed solar radiation used to vaporize water at Earth’s surface.  Energy released to the atmosphere when clouds form  Comparatively, large amounts of heat needed for phase changes of water  Sensible Heating  Heat transfer via conduction and convection that can be sensed by temperature change and measured by a thermometer

21. © AMS21 Heat Imbalance: Atmosphere vs. Earth’s Surface

22. © AMS22  Sensible heating, in the form of convectional uplifts, can combine with latent heating, through condensation, to channel heat from Earth’s surface into the troposphere  Produces cumulus clouds  If it continues vertically, cumulonimbus clouds form Heat Imbalance: Atmosphere vs. Earth’s Surface

23.  Bowen Ratio  Describes how energy received at the Earth’s surface is partitioned between sensible heating and latent heating  Bowen ratio = [(sensible heating)/(latent heating)]  At the global scale, this is [(7 units)/(23 units)] = 0.3 © AMS23 Heat Imbalance: Atmosphere vs. Earth’s Surface

24. © AMS24  Surface energy budget through the course of a year at Yuma, AZ and Madison, WI.  R = net radiation absorbed  H = sensible heating  LE = latent heating  G = storage

25. Heat Imbalance: Tropics vs. Middle and High Latitudes  Earth’s surface unevenly heated due to higher solar altitudes in the tropics than higher latitudes  Causes a temperature gradient, resulting in heat transfer  Poleward heat transport  Air mass exchange  Storms  Ocean currents © AMS25

26. © AMS26 Heat Imbalance: Tropics vs. Middle and High Latitudes  Heat transport by air mass exchange  North-south exchange of air masses transports sensible heat from the tropics into middle and high latitudes  Air mass properties of depend on source region  Modify as they move  Heat transport by storms  Tropical storms and hurricanes are greater contributors to poleward heat transport than middle latitude cyclones

27. © AMS27 The Gulf Stream flows along the East Coast from Florida to the Delaware coast.  Heat transport by ocean circulation  Contributes via wind-driven surface currents and thermohaline circulation  Thermohaline circulation is density- driven movement of water masses  Transports heat energy, salt, and dissolved gases over great distances and depths  Meridional overturning circulation (MOC)  At high latitudes, surface waters cool and sink, then flow southward as cold bottom water Heat Imbalance: Tropics vs. Middle and High Latitudes

28. © AMS28  Imbalances in radiational heating/cooling create temperature gradients  Earth’s surface the troposphere  Low and high latitudes  Heat transported in the Earth-atmosphere system to reduce temperature differences  Cause-and-effect chain starts with the Sun, ends with weather  Some solar radiation is absorbed (converted to heat), some to converted to kinetic energy  Causes winds, convection currents, and north-south exchange of air masses  Rate of heat redistribution varies by season  Causes seasonal weather and air circulation changes Why Weather?

29. © AMS29  Radiational controls  Factors that affect local radiation budget and air temperature  Time of day and time of the year  Solar altitude and duration of radiation  Cloud cover  Surface characteristics  Annual temperature cycle represents these variations  Annual temperature maximums and minimums do not occur at exact max/min of solar radiation, especially in middle and high latitudes  The atmosphere takes time to heat and cool  Average lag time in US = 27 days  Up to 36 days with the maritime influence Variation of Air Temperature

30. © AMS30 Variation of Air Temperature

31. © AMS31  Daily temperature cycle  Lowest temperature usually occurs just after sunrise  Based on radiation alone, minimum temperature would occur after sunrise when incoming radiation becomes dominant  Highest temperature usually occurs in the early to middle afternoon  Even though peak of solar radiation is around noon, imbalance in favor of incoming vs. outgoing radiation continues so the atmosphere also continues to warm Variation of Air Temperature

32. © AMS32 Variation of Air Temperature Daily Temperature Cycle

33. © AMS33  Surface cover  Dry soil heats more rapidly than moist  Less energy used to evaporate water  Especially in drought, energy used only to heat soil, soil becomes hotter  Relative humidity also affects evaporation  Snow  High albedo  Less energy absorbed by the surface or converted to heat  Snow reduces sensible heating of overlying air  Some of the available heat is used to vaporize snow  Snow is an excellent infrared radiation emitter  Nocturnal radiational cooling is extreme  When skies are clear, or light winds or calm conditions Variation of Air Temperature

34. © AMS 34 Variation of Air Temperature  Air mass advection  Horizontal movement of an air mass from one location to another  Cold air advection (A)  Horizontal movement of colder air into a warmer area  Warm air advection (B)  Horizontal movement of warmer air into a colder area  Significance of air mass advection to local temperature  Initial temperature of the air new mass  Degree of modification the air mass as travels over the Earth’s surface

35. © AMS35 Variation of Air Temperature  Urban heat island effect  City of warmth surrounded by cooler air  In a city:  Relative lack of moisture  Absorbed heat raises temperature (not for evaporation)  Greater concentration of heat sources (cars, air conditioners, etc)  Multiple reflections and lower albedo  Building materials conduct heat more readily than soil and vegetation  Develops best on nights when air is calm and sky is clear

36. © AMS36 Variation of Air Temperature Satellite-produced maps of Providence, RI (top) and Buffalo, NY (bott0m) highlighting the role that differences in development patterns/vegetation cover can have on a city’s urban heat island. Providence has a significantly stronger heat island signature. Buffalo, NY Providence, RI