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NATS 101
Lecture 6 TR
Temperature Variations
Term Project
Term Project Description
• One of Two Options
1. Scientific analysis of one of two films on
climate change.
2. Analysis of the daily afternoon weather
for Tucson over a three-week period.
Term Project
• Recommendations
1. Start project very soon. Preferably now.
2. Scientific exchange with other students is
OK, but the paper that you submit must be
your own and reflect your final thoughts.
3. Turnitin software will be used to identify
possible cases of plagiarism.
Temperature Questions
• What causes diurnal temperature variations?
• What physical processes can influence daily
temperature variations?
• Why is MAX temperature after solar noon?
• Why is MIN temperature just after sunrise?
• What is Wind Chill Factor? (if time allows)
MAX Temperature near Surface
Ahrens, Fig 3.1
1) Solar SW
3) Convection
2) Conduction
4) Air near ground is heated the most
MIN Temperature near Surface
1) Outgoing
Infrared
Ahrens, Fig 3.3
3) Absorbed
& Re-emitted
Infrared
2) Conduction
INVERSION – Temp
increases w/height
4) Air near ground is cooled the most
Daily Range of Temperatures
Ahrens, Fig 3.10
MAX-MIN
difference
decreases
with height
above ground
12 and 00 UTC
TUS Sounding
MAX-MIN Range
0oC at 700 mb-2400
m
2oC at 850 mb-800 m
6oC at 910 mb-150 m
12oC at 925 mbground
Range decreases
with height
Growth and Decay of Inversion
Height
Morning
Height
Evening
t4
t2
t3
t3
t4
t1
t2
t1
Temperature
Cooled the most at the ground level
Temperature
Warmed the most at the ground level
What Affects Inversion Strength?
Cloud Cover
Clear skies-strong inversion
Cloudy skies-weak inversion
Land Characteristics
Snow cover-strong inversion
Bare ground-weaker inversion
Wind Speed
Calm winds-strong inversion
Strong winds-weak inversion
Absorption Re-Emission
Weak IR
Strong IR
Warm
Cold
Mixing with Fast Winds
When Does MAX-MIN Occur?
When incoming Solar
exceeds outgoing IR
Temperature rises
When outgoing IR exceeds
incoming Solar
Temperature falls
When outgoing IR equals
incoming Solar
MAX occurs
Late afternoon
MIN occurs
Just after sunrise
Ahrens, Fig 3.2
Winter-Summer
Temperature
Variations at
Sea Level
DJF
100oF
10oF
Continents undergo
larger changes than
oceans
High latitudes undergo
larger changes than
low latitudes
JJA
Ahrens, Figs. 3.8, 3.9
Controls of Temperature
• Latitude
Average temperatures in middle latitudes
change by 5-10oC every 10o latitude change
• Elevation
Lapse rate in troposphere is 6.5oC/km
Tucson (2,500 ft)
July Max - 100oF
Mt. Lemmon (8,500 ft) July Max - 76oF
Controls of Temperature
• Ocean Currents and Prevailing Winds
Warm-Gulf Stream
Cold-California Current
• Land versus Water
Heat capacity of water is 5X that of land
Absorbed solar energy is distributed a
greater depth in water than in land
Specific Heat Capacity
Heat required to raise the temperature of
1 gm of mass 1oC.
Water has higher heat capacity than rock.
Material
Still Water
Specific Heat Capacity
(Cal gm-1 oC-1)
1.00
Dry Air
0.24
Granite (Rock)
0.19
Still water warms or cools very slowly
compared to air and land
Water-Soil Heating Depth
Consider the Fate of Incoming Solar Radiation
Penetrating Water vs. Soil
Deep
Penetration
Convective Conduction
Mixing
No mixing
Large Heat Capacity
Small warming over great depth
Shallow
Penetration
Small Heat Capacity
Large warming in shallow layer
Soil Temperature
Wallace and Hobbs
Ocean Temperature
Wallace and Hobbs
Wind Chill
Still air is poor conductor; lack of wind allows
insulating layer of still air to form next to skin
Wind blows insulating layer of air from skin
Forced convection or heat transport by advection
The main reason for seasons is?
1. Eccentricity of the earth’s orbit
2. Tilt of the earth’s axis (obliquity of the
ecliptic)
3. Precession of the equinox
4. Millennium variations in earth-to-sun
distances at aphelion and perihelion
Which statement is not a reason that
coastal sites experience less extreme
seasons than inland sites?
1. Water has a higher heat capacity than soil
2. Convective heat transfer is far more
efficient in water than soil
3. Water has a higher thermal conductivity
than soil
4. Sunlight penetrates deeper into water than
soil
Summary
• Balance between incoming and outgoing energy
controls temperature rises and falls
MAX late afternoon, MIN just after sunrise
• Diurnal temp. changes are largest at ground
Affected by wind, cloud cover, land type
• Winter-Summer differences
Largest over land, high latitudes
• Temperature controls
Latitude, Altitude, Land-Sea, Ocean Currents
Next Class Assignment
Atmospheric Moisture
• Reading - Ahrens
3rd-Pg: 75-86, B: 426, D: 429-432
4th-Pg: 77-89, B: 430, D: 433-436
5th-Pg: 79-91, B: 440, D: 443-446
• Homework03 - D2L (Due Monday Feb 8th)
3rd-Pg 106: 4.1, 4.2, 4.5, 4.6, 4.9, 4.10
4th-Pg 108: 4.1, 4.2, 4.5, 4.6, 4.9, 4.10
5th-Pg 108: 4.1, 4.2, 4.5, 4.6, 4.9, 4.10