Surface air temperature
Review of last lecture
• Earth’s energy balance at the top of the atmosphere and
at the surface. What percentage of solar energy is
absorbed by the surface?
• Atmospheric influences on radiation (3 ways)
• The three types of atmospheric scattering. What causes
the blue sky? Why causes the reddish-orange sunsets?
• What cause the greenhouse effect? What are the major
greenhouse gases? Why is methane important?
• Sensible heat flux (dry flux from warm to cold regions)
and latent heat flux (wet flux from wet to dry regions)
Temperature Basics
• Temperature – measure of average kinetic energy
•
(motion) of individual molecules in matter
Isotherms – maps, connect lines of equal temperature
Different temperature scales (units)
• All scales are relative
• degrees F = 9⁄5 degrees C + 32
• degrees K = degrees C + 273.15
Measurement of Temperature
Measurement of Temperature
• Thermometers are used to
measure temperature with either
mercury or alcohol.
• A maximum thermometer is
used to record daily temperature
maximums while a minimum
thermometer records minimums.
Instrument Shelters
• Weather instruments require
shelters that protect them from
solar radiation.
• They are painted white to create
a high albedo.
• Must be 5 ft from the ground
/surface to reduce laminar layer
bias.
Air Temperature and the Human Body
• Human comfort not only affected by temperature
• Two important considerations  wind and humidity
• Wind Chill Index
– relates temperature and wind speed
• Heat Index
– relates temperature and humidity
Wind Chill Index
Heat Index
Video: The 1995 Chicago heat wave
Seasonal variation of surface air temperature
Principal Controls on Temperature
1.
2.
3.
4.
5.
6.
Latitudinal variations in net radiation
Land-Water Contrasts
Atmospheric Circulation
Ocean Currents
Altitude
Local Effects
Controls on temperature
1. Latitudinal Variations in Net Radiation
• tropic-to-tropic – energy surplus
• poles – energy deficits
• ~ 38o N/S – balance
• imbalance of net radiation at surface
 Equator/Tropics vs. high latitudes
• drives global circulation
• agents: wind, ocean
currents,
weather systems
Daily/Seasonal Radiation Patterns
• insolation peak vs. temperature
• daily lag
• seasonal lag
• Lag is function of type of surface, wetness, wind, etc
Seasonal
Temp
Distributions
• T decreases poleward
• larger T gradient in winter
• isotherms shift seasonally
• T over land > water in summer
• NH steeper T gradient
Controls on temperature
2. Land-water contrasts
• Surface influences heating
• Heat Capacity – water > land… (water takes longer heat/cool)
• Mixing – fluids can be physically mixed
• Transparency – greater penetration (distributed over greater volume)
• Evaporation – consumes large amount of energy – big over water
Temperature Ranges (Summer minus Winter)
Large over land, small over ocean
Controls on temperature
3. Atmospheric circulation
• large scale circulation patterns resulted from pressure differences (gradients)
• generates winds  move warm/cold air around  affects temperature
• influences cloud cover
Controls on temperature
4. Ocean currents
Infrared Satellite image of the Gulf Stream
Red/orange = 25-29oC
Yellow/green = 17-24oC
Blue = 10-16oC
Purple = 2-9oC
Controls on temperature
5. Altitude
• Temperature decreases with increasing altitude
 ground acts as heat source
Controls on temperature
6. Local effects
• slope orientation: North v. South-facing slopes
 temperature/moisture regimes  vegetation
forested v.
open fields
Summary
• Temperature, 3 units
• 6 factors controlling temperature