ENERGY, HEAT AND TEMPERATURE

1 4/30/2020 (c) Vicki Drake, SMC

ENERGY

  The ability or capacity to perform work on some form of matter   Matter is any substance that takes up space and has mass Earth’s atmosphere is considered ‘matter’ – all the gas molecules and particulates Energy may be considered as either

Kinetic

or

Potential

 Source of Energy for Earth: Sun  Lecture will describe how the Sun’s energy works on Earth’s atmosphere 4/30/2020 (c) Vicki Drake, SMC 2

Potential Energy

 Stored Energy:  Value of potential energy (PE) determined by work capability  Total amount of stored energy due to position  Potential energy examples:  A battery  Water behind a dam  Any object lifted against pull of gravity 4/30/2020 (c) Vicki Drake, SMC 3

Kinetic Energy

 Energy in motion  Value of Kinetic Energy (KE) is determined by the speed and mass of object  Examples of atmospheric KE  Heat energy  Solar energy  Light energy  Electrical energy 4/30/2020 (c) Vicki Drake, SMC 

E k = ½ mv

energy,

m 2

where

E k

is kinetic is the mass of the object and

v 2

is the square of the velocity of the mass 4

Internal Energy

 Internal Energy is the stored PE and KE of atoms and molecules in any kind of matter or substance  In theory:

PE = KE

 The energy associated with random, disordered motion of molecules 4/30/2020 (c) Vicki Drake, SMC 5

1

st

Law of Thermodynamics (Newton)



Conservation of Energy

:  Energy cannot be created or destroyed. It can only change form (i.e., converted to another type of energy).

 Energy is a constant in the universe  Conversion of Energy examples:  Heater/Furnace: Chemical → Heat  Automobile Engine: Chemical → Mechanical  Nuclear: Heat → Kinetic → Optical  Battery: Chemical Sound or Mechanical or Optical or… 4/30/2020 (c) Vicki Drake, SMC 6

Temperature: Measuring Energy

 Temperature is a measurement of the

average

kinetic energy of atoms/molecules in a substance  Temperature is measured using a Thermometer  A thermometer measures the temperature of a system in a quantitative way.

 ‘Mercury-in-glass’ type has a bulb filled with mercury that expands into a capillary when warmed.

 Rate of expansion calibrated on glass scale 4/30/2020 (c) Vicki Drake, SMC 7

Thermometer Scales: Interpreting Energy

  

Fahrenheit

 : developed by Gabriel Fahrenheit in the 1700s.

Boiling point of water: 212 0  Freezing point of water: 32 0

Celsius

measure  : developed by Carolus Linnaeus using ‘centrigrade’ Boiling point of water: 100 0  Freezing point of water: 0 0

Kelvin:

 An absolute temperature scale, based on Absolute Zero, developed by William Thompson and Lord Kelvin Boiling point of water: 373K  Freezing point of water:273K  Absolute Zero: 0 degrees K  -273 0 C or -459 0 F 4/30/2020 (c) Vicki Drake, SMC 8

What is Heat Energy?

 Heat represents energy in the process of being transferred from one object to another because of a temperature difference.

 Heat energy transfers are ‘one-way’ in natural environment 

Heat energy transfer is from warmer objects to colder objects

4/30/2020 (c) Vicki Drake, SMC 9

What is Heat Capacity?

 The ratio of the amount of heat energy absorbed by a substance  Heat capacity is measured by a temperature increase in the receiving object that corresponds to the amount of heat energy applied to that object 

Rapid temperature increase means the substance has a low heat capacity



Slow temperature increase means the substance has a high heat capacity

4/30/2020 (c) Vicki Drake, SMC 10

  

What is

Specific Heat

Capacity?

The amount of heat required to raise the temperature of 1 gram (1 g) of any substance by 1 degree Celsius  All objects have their own increase

specific heat

capacity – the rate at which they will absorb heat energy and register a temperature  The specific heat capacity of

water

all other substances are measured is the baseline against which Water has a baseline

specific heat

capacity of 1.0, while soil has a

specific heat

capacity of 0.2 (as measured against water).

Water can absorb 5 times more heat energy than ‘soil’ before a temperature increase is registered. 

Water has a high specific heat capacity



Water heats slowly and releases heat slowly



Soil has a low specific heat capacity



Soil absorbs heat energy quickly and releases heat energy quickly

4/30/2020 (c) Vicki Drake, SMC 11



Latent Heat – “Hidden Heat”

Latent heat is energy absorbed and/or released by a substance during a ‘change of phase’ or ‘change of state of being’.

 Latent heat is measured according to

water’s

response to absorbing or releasing energy.

 Water is the only substance that exists in all three ‘states of being’ at the same time at earth’s ambient temperature and air pressure.

 Solid (ice  Liquid (water)  Gas (water vapor) 4/30/2020 (c) Vicki Drake, SMC 12

Latent Heat and Change of Phase: Absorption and Release of Energy

4/30/2020 (c) Vicki Drake, SMC 13

Latent Heat – “Hidden Heat”

’  When change of phase is from a solid to a liquid and then to a gas, heat energy is absorbed.

 This heat is ‘latent’ heat and cannot easily be measured as the ice melts into liquid water and then evaporates into water vapor.

 When the change of phase is from a gas to a liquid to a solid, heat energy is released into the surrounding atmosphere.

 This heat is also ‘latent’ heat, but the resulting increase in temperature of the surroundings can be measured as the water vapors condenses into droplets and then into ice crystals.

4/30/2020 (c) Vicki Drake, SMC 14

Change of Phase: Water

 

Evaporation

 – heat energy absorbed by a substance changing water from a liquid to a gas (vapor) phase Evaporation is a ‘cooling’ process for a surface as heat energy is absorbed by water droplets, converting to a vapor, from surrounding atmosphere – “Latent Heat” (not easily measured)

Condensation

changing from a gas to a liquid phase 

–

heat energy released by a water Condensation is a ‘heating’ process for a surface as heat energy is released by water vapor, converting to liquid droplets, into surrounding atmosphere – “Latent Heat” (easily measured as “Sensible Heat”) 4/30/2020 (c) Vicki Drake, SMC 15

Latent Heat’s Role in Energy

   Latent heat is an important source of energy in atmosphere Heated water vapor molecules released during evaporation are swept to higher latitudes and altitudes  Condensation of vapor to liquid releases heat energy to upper atmosphere Main energy source for:  Thunderstorms   Hurricanes Other mid-latitude cyclonic storms 4/30/2020 (c) Vicki Drake, SMC 16

Heat Transportation Mechanisms in the Atmosphere

 Three processes work together to transport heat energy throughout the atmosphere and around the globe.

 Conduction  Convection  Radiation 4/30/2020 (c) Vicki Drake, SMC 17

Conduction

 Molecule-to-molecule transfer of heat energy  Heat flows from warm to cold  The greater the temperature difference, the more rapid the heat exchange  Effective only in lower atmosphere where molecules are ‘compressed’ at the surface 4/30/2020 (c) Vicki Drake, SMC 18

Convection

   Transfer of heat by currents in a fluid (liquid or gas) Uneven heating of Earth’s surface sets up conditions of warm air rising and cooler air sinking:

Thermals

Important part of heat transfer by expansion, rising, cooling and sinking of air within the lower atmosphere 4/30/2020 (c) Vicki Drake, SMC 19

Radiation

 Radiant energy traveling in waves that release energy when they are absorbed by an object  Waves have both magnetic and electric properties: ElectroMagnetic Spectrum  Energy travels at the speed of light (C):  300,000 km/sec  186,000 miles/sec  EM Spectrum – total amount of solar energy from Sun 4/30/2020 (c) Vicki Drake, SMC 20

Characteristics of Radiant Waves

  Crests and troughs Wavelength (

λ

) –  Distance from one crest to another  Measured in units of meters, centimeters, micrometers (10 -6 ) and nanometers (10 -9 )  Higher energy waves have short wavelengths (higher frequency) 4/30/2020 (c) Vicki Drake, SMC 21

Radiation – Temperature Connection

 All objects in universe (above Absolute Zero of -273K) emit radiation  The higher the temperature of the object, the greater the amount of radiation emitted  Stephen Boltzmann’s law:

E~ σT 4



E

= Maximum rate of radiation emitted per square meter of an object 

σ



T

= a constant (5.67 x 10 -8 W/m 2 K 4 ) = Temperature of the object (in Kelvin) 4/30/2020 (c) Vicki Drake, SMC 22

Radiation: Solar Energy vs Earth Energy

 Solar energy = 6000 K (10,500 0 F)  Earth energy = 288 K (59 0 F, 15 0 C) 

λ

max

for the Sun: ~0.5

μ

m (micrometer)  the wavelength for “Blue” in the Visible Light portion of EM 

λ

max

for the Earth: 10

μ

m (micrometer)  the wavelength for Far Infrared (heat energy) in the EM Spectrum 4/30/2020 (c) Vicki Drake, SMC 23

Earth Energy Balance

4/30/2020 (c) Vicki Drake, SMC 24

Daily Temperature Variations



Daily Temperature Lag

 Continual warming of air at Earth’s surface after Sun as reached solar peak at Noon  Graph depicts the time of maximum insolation at local noon, while the maximum air temperatures occur past local noon 4/30/2020 (c) Vicki Drake, SMC 25

Daytime Heating

      Air closest to surface heats through

conduction convection

processes and

Conduction

is not effective – strong temperature differences found just above surface

Convection

vertically of warm rising air (

Thermals

) redistribute air Sun is most intense at local Solar Noon (“local meridian”) Post-meridian (p.m.):

insolation

solar radiation) continues to be greater than outgoing longwave heat energy from Earth (incoming shortwave Energy surplus develops for 2-4 hours after Solar Noon  Lag time develops between solar maximum and maximum heating of Earth’s surface 4/30/2020 (c) Vicki Drake, SMC 26

Nighttime Cooling

  Lowered Sun angle, initially, spreads energy over wider area, reducing heat available to surface Earth’s surface and lower atmosphere lose more heat energy than gained   Ground and air cooling via

radiational cooling

from Earth’s surface over night Night progresses – Earth’s surface and air layer closest to surface are cooler than upper level air  Coldest time of 24-hour day? Just before sunrise!

4/30/2020 (c) Vicki Drake, SMC 27

Seasonal Lag time – Northern Hemisphere

 Over the year – the Earth’s temperature shows a temperature lag behind the Sun’s insolation 4/30/2020 (c) Vicki Drake, SMC 28

Temperature Data

 Diurnal Range of Temperature  Difference between daily maximum and daily minimum temperatures  Largest diurnal range: Dry, arid regions  Low specific heat of soils  Smallest diurnal range: Wet, humid regions  High specific heat of water 4/30/2020 (c) Vicki Drake, SMC 29

What does diurnal range tell us?

 Regions that have a low diurnal range are usually located near a body of water  Regions that have a high diurnal range are usually located away from water 4/30/2020 (c) Vicki Drake, SMC 30

Mean and Average Daily Temperature

 Average: Add all hourly values/24  Mean: Add Highest hourly value and Lowest hourly value/2  Collecting the average of mean daily temperatures for a particular location on a particular day for a 30-year period is the ‘normal’ or ‘average’ temperature for that place on that day 4/30/2020 (c) Vicki Drake, SMC 31

Average Monthly Temperature

 The average of the mean daily temperatures for a month  Add all the mean daily temperatures, divide by the total number of days in the month (‘average’)  Mean average monthly temperature:  Add the highest mean daily temperature for the month to the lowest mean daily temperature for the month and divide by 2 4/30/2020 (c) Vicki Drake, SMC 32

Annual Range of Temperature

 The difference between the average temperature of the warmest month and coldest month  Largest range – areas dominated by land  “Continental” climates  Smallest range – areas dominated by water  “Maritime” climates 4/30/2020 (c) Vicki Drake, SMC 33

Mean Annual Temperatures

 The average temperature for any place for an entire year  Add mean temperature for the warmest month to the mean temperature for the coldest month and divide by 2.

 Add all the average temperatures for each month (12 months) and divide by 12.

4/30/2020 (c) Vicki Drake, SMC 34

Controls on Temperature

 # 1 control: amount of incoming solar radiation (insolation) reaching the Earth  Seasonal shift of insolation due to rotation, revolution and tilt of Earth’s axis  Latitude:  Temperatures near Equator are more consistent year-round  Further away from Equator – more variability of temperatures and cooler overall 4/30/2020 (c) Vicki Drake, SMC 35

Latitude as a Temperature Control

4/30/2020 (c) Vicki Drake, SMC 36

Unequal Heating of Land and Water

 The difference in the specific heat of soils and water sets up conditions of differential heating and cooling of the land and water  Specific heat of water is greater than the specific heat of ‘land’  ‘Land’ heats and cools at a faster rate than large bodies of water 4/30/2020 (c) Vicki Drake, SMC 37

Ocean Currents

  Ocean currents move cool polar waters to the tropics as well as moving warm tropical waters to the poles.

Two types of ocean currents:  Warm ocean currents  Cool ocean currents 4/30/2020 (c) Vicki Drake, SMC 38

Elevation

   The lower atmosphere (

troposphere)

cools at a fairly consistent rate from lower to higher elevations Lapse rate: a change in temperature with a change in elevation Environmental lapse rate is the average cooling/heating rate for rising/sinking air  ~6 0 C/`1000 meters  ~3.3

0 F/1000 feet 4/30/2020 (c) Vicki Drake, SMC 39

Albedo of Earth’s surfaces

    Albedo is the amount of energy reflected back to space by different types of surfaces Ice/Snow have the highest albedo – the highest reflectance, low absorbance Vegetation has a low albedo absorbance – low relfectance, high Water has a low albedo, high absorbance 4/30/2020 (c) Vicki Drake, SMC 40