Transcript Temperature and Heat

NATS 101
Lecture 3 TR
Weather & Climate
Temperature
Heat Transfer
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3” by 5” Cards
• Name
• SID
• Clicker Number
• Clicker Setup Instructions
2
What is Pressure at 0.8 km?
(Tucson, Arizoina)
Use Equation for Pressure Change
p(at elevation Z in km)  pMSL  10 Z /(16 km)
set Z = 0.8 km, pMSL  1013 mb
p(0.8 km)  1013mb  10(0.8km)/(16 km)
p(0.8 km)  1013mb  100.05
p(0.8 km)  1013mb  0.891 903mb
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What is Pressure at 1.6 km?
(Denver, Colorado)
Use Equation for Pressure Change
p(at elevation Z in km)  pMSL  10 Z /(16 km)
set Z = 1.6 km, pMSL  1013 mb
p(1.6 km)  1013mb  10(1.6 km)/(16 km)
p(1.6 km)  1013mb  100.10
p(1.6 km)  1013mb  0.794  805mb
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What is Pressure at 8.7 km?
(Mt. Everest)
Use Equation for Pressure Change
p(at elevation Z in km)  pMSL  10 Z /(16 km)
set Z = 8.7 km, pMSL  1013 mb
p(8.7 km)  1013mb  10(8.7 km)/(16 km)
p(8.7 km)  1013mb  100.54375
p(8.7 km)  1013mb  0.286  290 mb
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Weather
Weather – The state of
the atmosphere:
for a specific place
at a particular time
Weather Elements
1) Temperature
2) Pressure
3) Humidity
4) Wind
5) Visibility
6) Clouds
7) Significant Weather
Lecture 2-Nats 101
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Surface Station Model
Responsible for boxed parameters
Ahrens, p 431
Temperatures
Plotted °F in U.S.
Sea Level Pressure
Leading 10 or 9 is
not plotted
Examples:
1013.8 plotted as 138
998.7 plotted as 987
1036.0 plotted as 360
Lecture 2-Nats 101
7
Sky Cover and Weather Symbols
Ahrens, p 431
Ahrens, p 431
Lecture 2-Nats 101
8
Wind Speed
How to read:
Half barb = 5 knots
Full barb = 10 knots
Flag = 50 knots
1 knot = 1 nautical mile per hour = 1.15 mph
= ______ knots
Wind direction
NORTHERLY
From the north
360°
270°
WESTERLY
From the west
180°
90
°
EASTERLY
From the east
SOUTHERLY
From the south
Surface Station Model
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111
Decimal point
What are Temp, Dew Point,
SLP, Cloud Cover, Wind
Speed and Direction?
Ahrens, p 431
Temperate (oF)
Pressure (mb)
Last Three Digits
(tens, ones, tenths)
Dew Point (later)
Moisture
Wind Barb
Direction and Speed
Cloud Cover
Tenths total coverage
Lecture 2-Nats 101
14
Practice Surface Station
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998
Decimal point
What are Temp, Dew Point,
SLP, Cloud Cover, Wind
Speed and Direction?
Sea Level Pressure
Leading 10 or 9 is
not plotted
Examples:
1013.8 plotted as 138
998.7 plotted as 987
1036.0 plotted as 360
Ahrens, p 431
Lecture 2-Nats 101
15
SLP pressure
temperature
dew point
Ohio State website
Lecture 2-Nats 101
cloud cover
wind
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Surface Map Symbols
• Fronts
Mark the boundary
between different
air masses…later
Significant weather
occurs near fronts
Current US Map
Ahrens, p 432
Lecture 2-Nats 101
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So what’s happening
above the ground?
Radiosonde
Weather balloons, or
radiosondes, sample
atmospheric to 10 mb.
They measure
temperature
moisture
pressure
They are tracked by
GPS to get winds
Lecture 2-Nats 101
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Radiosonde Distribution
Radiosondes released
at 0000 and at 1200
GMT for a global
network of stations.
Large gaps in network
over oceans and in
less affluent nations.
Stations ~400 km apart
over North America
Lecture 2-Nats 101
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What is Climate?
Statistics of weather (averages, ranges,
extremes) computed over many years.
Year (annual precipitation for Tucson)
Season (e.g Winter: Dec-Jan-Feb)
Month (e.g January rainfall in Tucson)
Date (e.g. Average & record high and lows
temperatures for Jan 30 in Tucson)
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Climate of Tucson
Monthly Averages
Average Temperature = (MAX+MIN)/2
Individual months can show significant
deviations from long-term, monthly means.
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Average and Record
MAX and MIN
Temperatures for Date
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Climate of Tucson
Probability of Last Spring Freeze
Cool Site: Western Region Climate Center
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Climate of Tucson
Probability of Rain
Cool Site: Western Region Climate Center
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Climate of Tucson
Extreme Rainfall
Cool Site: Western Region Climate Center
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Climate of Tucson
Snow!
Cool Site: Western Region Climate Center
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Summary
• Weather - atmospheric conditions at
specific time and place
Weather Maps => Instantaneous Values
• Climate - average weather and the range
of extremes compiled over many years
Statistical Quantities => Expected Values
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Temperature Scales
• Fahrenheit (oF) - relative
US public standard
• Celsius (oC) - relative
Freezing point 0oC
Boiling point 100oC
o
C= 5/9 (oF-32)
• Kelvin (K) - absolute
K= oC+273
Ahrens p27
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What is Temperature?
Microscopic View
Energy due to random
velocity of molecules
Related to average
molecular speed;
500 m/s at room
temperature for air
Maxwell Distribution
K.E.=(1/2)mv2=(3/2)kT
m=molecular weight
k=Boltzmann constant
=1.38065×10−23 joule/K
(joule is unit of energy)
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Temperature-Density: Charles Law
V  constant
T(K) = constant x Volume
at uniform pressure
Consider volume of air
If air is warmed:
The molecules will move
faster, have “stronger”
collisions, and tend to
become spaced farther
apart
Volume increases, so
density decreases
Warmer => less dense
Charles Law Applet
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What is Heat?
Williams, p. 19
Heat-Energy in the
process of being
transferred from a
warmer object to a
cooler object
Consider a pot of water
on a hot burner.
Consider the following
questions:
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Heat Transfer Questions
Williams, p. 19
What causes the…
Pan bottom and handle
to get warmer?
Top of the water to
become warmer?
Water temperature to
not exceed 100oC?
Region away from side
of pan to feel warm?
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Conduction
Heat transfer due to collision of molecules.
Conduction warms the bottom of the pan!
Conductivity - rate of heat transfer across a 1 cm thick
slab of material if one side is kept 1oC warmer than the
other
Do a Cheap Experiment: Touch metal on your chair!
0oC
Heat
Transfer
Metal
Water
Air
1 cm
1o C
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Heat Conductivity
Material
Still Air
Dry Soil
Still Water
Wet Soil
Granite (Rock)
Iron (Metal)
Silver (Metal)
Heat Conductivity
(Cal s-1 cm-1 oC-1)
6.1 x 10-5
6.0 x 10-4
1.4 x 10-3
5.0 x 10-2
6.5 x 10-2
0.16
1.01
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Convection
Heat transfer due to vertical exchange of mass
Occurs in fluids (liquids, gases) because of gravity
Warm, buoyant air rises - Cool, dense air sinks
Convection warms top of liquid!
Cool
Warm
heat below - convection
gravity
Warm
Cool
heat side - convection
gravity
Warm
Cool
heat top - no convection
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Convection Movies
2D Convection Tank Animation 
2D Convection Model Ra=10**6
2D Convection Model Ra=10**7 IC1
2D Convection Model Ra=10**7 IC2
3D Rayleigh-Benard Convection Model 
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Energy States and Water Phases
SOLID
water molecules are
tightly packed in a
crystal alignment that
prevents them from
changing shape
LOW ENERGY STATE
Small Energy Change
LIQUID
attractive forces btw
molecules weaken and
individual molecules
can move around each
other, but they can not
break away
SLIGHTLY HIGHER
ENERGY STATE
VAPOR
water molecules move
very rapidly and are
not bound together
EXTEMELY HIGH
ENERGY STATE
Large Energy
Change
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Latent Heat
Surrounding air cools
More
Ordered
Phase
Strong
attraction
between
molecules
Less
Ordered
Phase
-620 cal/gm
-80 cal/gm
-540 cal/gm
Some
attraction
+540 cal/gm
+80 cal/gm
Weak
attraction
between
molecules
+620 cal/gm
Surrounding air warms
Ahrens, p 28
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Modes of Heat Transfer
Latent
Heat
Williams, p. 19
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Take Home Points
• Heat-Energy transfer due to temperature
differences
Three modes of heat transfer
Conduction – molecule to molecule
Convection – transport of fluid
Radiation – electromagnetic waves
Next lecture!
• Latent Heat – energy of phase changes
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Next Class Assignment
Radiation
• Reading - Ahrens
3rd: 30-42
4th: 30-42
5th: 30-42
• Homework01 - D2L (Due Monday Jan 25th)
3rd-Pg 52: 2.7, 9, 10, 11, 12
4th-Pg 52: 2.7, 9, 10, 11, 12
5th-Pg 52: 2.7, 9, 10, 11, 12
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