nats 101 lecture 8 temperature variations. supplemental references for today’s lecture wallace, j....
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NATS 101
Lecture 8Temperature Variations
Supplemental References for Today’s Lecture
Wallace, J. M. and P. V. Hobbs, 1977: Atmospheric Science, An Introductory Survey. 467 pp. Academic Press. (ISBN 0-12-732950-1)
Review
• Seasons Due to Tilt of Earth’s Axis
Affects Two Things:
Solar Zenith Angle - Length of Day
• Differential Solar Heating and IR Cooling
Cause of Atmospheric-Ocean Motions
Is Longest Day the Hottest Day?
USA Today WWW Site
Consider Average Daily Temperature for Chicago IL:
Annual Energy Balance
Heat transfer done by winds and ocean currentsDifferential heating drives winds and currents
We will examine later in course
NH SH
Radiative WarmingRadiative
CoolingRadiative Cooling
Ahrens, Fig. 2.21
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
ConvectionConvection
ConductionConduction
Solar SWSolar SW
Ahrens, Fig 3.1
Air at ground level is heated the most
MIN Temperature near SurfaceAhrens, Fig 3.3Outgoing Outgoing
InfraredInfrared
Absorbed & Absorbed & Re-emitted Re-emitted
InfraredInfrared
ConductionConduction
INVERSION – Temp decreases w/height
Air at ground level is cooled the most
Daily Range of TemperaturesAhrens, Fig 3.10
MAX-MIN difference decreases with height above ground
12 and 00 UTC TUS Sounding
MAX-MIN Range
12oC at 925 mb
6oC at 910 mb
2oC at 800 mb
0oC by 700 mb
Range decreases Range decreases with heightwith height
isoth
erm
sisobars
Diurnal Range
Inversion
Temperature
Hei
ght
t1
t2
t3
Temperature
Hei
ght
t2
t3
t1
t4
Growth and Decay of Inversion Evening Morning
t4
Cooled the most at the ground level Warmed the most at the ground level
What Affects Inversion Strength?
Cloud CoverCloud CoverClear skies-strong inversionCloudy skies-weak inversionLand CharacteristicsLand CharacteristicsSnow cover-strong inversionBare ground-weaker inversionWind SpeedWind SpeedCalm winds-strong inversionStrong winds-weak inversion
Weak IR Strong IR
Absorption Re-Emission
Warm
Cold
Mixing with Fast Winds
When Does MAX-MIN Occur?When incoming SW
exceeds outgoing IRTemperature rises
When outgoing IR exceeds incoming SWTemperature falls
When outgoing IR equals incoming SWTemp. is constant
MAX occurs Late afternoon
MIN occurs Just after sunrise
Ahrens, Fig 3.2
Winter-Summer Temperature Variations at
Sea Level
Continents undergo larger changes than oceans
High latitudes undergo larger changes than low latitudes
Ahrens, Figs. 3.8, 3.9Ahrens, Figs. 3.8, 3.9100100ooFF 1010ooFF
DJFDJF
JJAJJA
Ahrens, Figs. 3.8, 3.9Ahrens, Figs. 3.8, 3.9100100ooFF 1010ooFF
DJFDJF
JJAJJA
Winter-Summer Temperature Variations at
Sea Level
Continents undergo larger changes than oceans
High latitudes undergo larger changes than low latitudes
Controls of Temperature
• Latitude
Average temperatures in middle latitudes decrease by 5-10oC every 10o latitude
• 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 temperature of 1 gm of mass 1oC.
Rock has lower heat capacity than water
Material Specific Heat Capacity (Cal gm-1 oC-1)
Still Water 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
Deep Penetration
Shallow Penetration
Consider Incoming Solar Energy
Penetrating Water-Soil
Convective Mixing
Small warming over great depth Large warming in shallow layer
Conduction No mixing
Large Heat Capacity Small Heat Capacity
Wallace and Hobbs, p347
Soil Temperature
Wallace and Hobbs, p348
Ocean Temperature
Wind Chill
Still air is poor conductor; lack of wind allows insulating layer of still air to form near skin
Wind blows insulating layer of air from skin Forced convection or heat transport by advection
Summary • Balance between incoming and outgoing energy
controls temperature rises and fallsMAX late afternoon, MIN just after sunrise
• Diurnal temp. changes are largest at groundAffected by wind, cloud cover, land type
• Winter-Summer changesLargest over land, high latitudes
• Temperature ControlsLatitude, Altitude, Land-Sea, Ocean Currents
Assignment
• Ahrens
Atmospheric Moisture
Pages 77-89, B: 430, D: 433-436
Problems 4.1, 4.2, 4.5, 4.6, 4.9, 4.10