Transcript ENERGY, HEAT AND TEMPERATURE

ENERGY, HEAT AND
TEMPERATURE
7/20/2015
(c) Vicki Drake, SMC
1
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
7/20/2015
(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
7/20/2015
(c) Vicki Drake, SMC
3
Kinetic Energy
 Energy in motion
Value of Kinetic Energy
(KE) is determined by
the speed and mass of
object
Ek = ½ mv2 where Ek is kinetic
energy, m is the mass of the object
and v2 is the square of the velocity
of the mass
 Examples of
atmospheric KE
Heat energy
Solar energy
Light energy
Electrical energy
7/20/2015
(c) Vicki Drake, SMC
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
7/20/2015
(c) Vicki Drake, SMC
5
1st 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…
7/20/2015
(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
7/20/2015
(c) Vicki Drake, SMC
7
Thermometer Scales: Interpreting Energy
 Fahrenheit: developed by
Gabriel Fahrenheit in the 1700s.
 Boiling point of water: 2120
 Freezing point of water: 320
 Celsius: developed by Carolus
Linnaeus using ‘centrigrade’
measure
 Boiling point of water: 1000
 Freezing point of water: 00
 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
 -2730C or -4590F
7/20/2015
(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
7/20/2015
(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
7/20/2015
(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 specific heat capacity – the rate at
which they will absorb heat energy and register a temperature
increase
 The specific heat capacity of water is the baseline against which
all other substances are measured
 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
7/20/2015
(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)
7/20/2015
(c) Vicki Drake, SMC
12
Latent Heat and Change of Phase:
Absorption and Release of Energy
7/20/2015
(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.
7/20/2015
(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 – heat energy released by a water
changing from a gas to a liquid phase
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”)
7/20/2015
(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
7/20/2015
(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
7/20/2015
(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
7/20/2015
(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
7/20/2015
(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):
 EM Spectrum – total amount of
solar energy from Sun
 300,000 km/sec
 186,000 miles/sec
7/20/2015
(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)
7/20/2015
(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~σT4
E = Maximum rate of radiation emitted per
square meter of an object
σ = a constant (5.67 x 10-8 W/m2K4)
T = Temperature of the object (in Kelvin)
7/20/2015
(c) Vicki Drake, SMC
22
Radiation: Solar Energy vs Earth Energy
Solar energy = 6000 K (10,5000F)
Earth energy = 288 K (590F, 150C)
λmax for the Sun: ~0.5 μm (micrometer)
the wavelength for “Blue” in the Visible Light
portion of EM
λ max for the Earth: 10 μm (micrometer)
the wavelength for Far Infrared (heat energy) in
the EM Spectrum
7/20/2015
(c) Vicki Drake, SMC
23
Earth Energy Balance
7/20/2015
(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
7/20/2015
(c) Vicki Drake, SMC
25
Daytime Heating
 Air closest to surface heats through conduction and
convection processes
 Conduction is not effective – strong temperature
differences found just above surface
 Convection of warm rising air (Thermals) redistribute air
vertically
 Sun is most intense at local Solar Noon (“local meridian”)
 Post-meridian (p.m.): insolation (incoming shortwave
solar radiation) continues to be greater than outgoing
longwave heat energy from Earth
 Energy surplus develops for 2-4 hours after Solar Noon
 Lag time develops between solar maximum and maximum
heating of Earth’s surface
7/20/2015
(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!
7/20/2015
(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
7/20/2015
(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
7/20/2015
(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
7/20/2015
(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
7/20/2015
(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
7/20/2015
(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
7/20/2015
(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.
7/20/2015
(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
7/20/2015
(c) Vicki Drake, SMC
35
Latitude as a Temperature Control
7/20/2015
(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
7/20/2015
(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
7/20/2015
(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
 ~60C/`1000 meters
 ~3.30F/1000 feet
7/20/2015
(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 – low
relfectance, high
absorbance
 Water has a low
albedo, high
absorbance
7/20/2015
(c) Vicki Drake, SMC
40