GEOG101: Physical Geography
Lecture 07: Wednesday, Feb. 4, 2009
Topics
1. Temperature Concepts and Measurement
2. Principal Temperature Controls
3. Earth's Temperature Patterns
4. Air Temperature and the Human Body
Temperature Concepts and Measurement
• Heat is a form of energy that flows from one system or object to another!
• Temperature is a measure of average kinetic energy (motion) of individual molecules in matter!
• Temperature and heat are related because changes in T are caused by the absorption or emission (gain or loss) of heat energy!
• Temperature Scales (Fahrenheit, Celsius, Kelvin)
Absolute zero degree: The temperature at which all atomic and molecular motion in matter stops
Absolute zero degree in different scales: -459.4 degree F; -273 degree C; 0 degree K;
Scientific research uses the Kelvin scale because it starts at absolute zero and thus the readings are proportional to the actual kinetic energy in a material!
Internationally Celsius scale is the most popular -- Melting point of ice is 0 degree C and the boiling point of water is 100 degree C!
US remains the only major country still using the Fahrenheit scale -- C = (5/9)*(F-32)
• Temperature measurement:
Principle -- expansion of fluids: When fluids are heated, they expand; upon cooling, they contract!
Mercury vs. Alchol Thermometers: which one is needed for measuring temperatures lower than -50 degree C?
• Standard Official T readings: 1.2-1.8 m above the ground surface, shelters, anf ventilation
Daily mean T: an average of daily minimum-maximum readings;
Monthly mean T: total daily mean Ts for the month divided by the number of days in the month;
Annual T range: difference between the lowest and highest monthly mean T for a given year
Principal Temperature Controls
• Latitude
Affects insolation: (1) low latitude locations have higher annual T and less difference between Tmax and Tmin, (2) High latitude locations have lower annual T and larger difference between Tmax and Tmin
• Altitude
High altitude has greater daily range
Thinner atmosphere has less ability to absorb and radiate heat
High altitude has lower annual average (Normal lapse rate: 6.4 degree C/1000 m)
• Cloud Cover
cause albedo
Reduce the insolution – you want shadows in summer
Moderate temperatures – cooler days, warmer nights
Cloudy nights are warmer because clouds absorb heat energy and reradiate some of it back to the ground
• Land-Water Heating Differences
Evaporation: Cause a negative feedback – the ocean Temperature rarely rises above 31 degree C (88 degree F)
Transparency: Photic zone in the ocean (aveg. 60 m)
Specific heat: the heat capacity of a substance--Water can hold more heat than can soil or rock: day-to-day T change near a substantial water body tends to be moderated!
Movement--Cooler and warmer water can mix, spreading the available energy over a greater volume
Ocean currents and sea surface temperatures
Marine vs. continental effects: (1) Marine effect, or
Maritime: influencing locations along coastlines or on island--mild T range on both daily and yearly basis; (2) Continental effect, or Continentality: Inland areas far away from ocean--a greater range of Tmax and Tmin on both daily and yearly basis
Earth's Temperature Patterns
• Isotherms: isolines that connects points of equal temperature, thus portrays the T patterns -- Similar to contour lines on a topographic map
• Thermal equator: an isotherm connecting all points of highest temperature
• January Temperature Map
Thermal equator movement southward
More pronounced over large continents
• July Temperature Map
Thermal equator movement northward
More pronounced over large continents
• Annual Temperature Range Map: Maritime vs. Continentality
Low latitudes: lowest annual temperature ranges on Earth
Subpolar latitudes: highest annual temperature ranges
Southern Hemisphere: less seasonal T variations. WHY?
Air Temperature and the Human Body
• Wind chill - body heat loses to the air
Correlates cold and wind speed
Higher wind speed -- more heat loss
• Heat index (HI)
Correlates heat and humidity