Lecture 5: Global Temperatures
Temperature and Heat
Temperature = measure of the average energy of motion,
called kinetic energy, of particles of matter.
Æ cannot flow (just kinetic energy)
Heat = energy transferred from one body/thermodynamicsystem to another due to thermal contact when the systems are
at different temperatures.
Æ can flow (kinetic AND potential energy)
Geog 1000 Introduction to Physical Geography Fall 2013 : Dr. Hester Jiskoot, University of Lethbridge
Temperature scales
1) Kelvin : kinetic energy of molecules (abs. zero)
2) Celcius : thermal behaviour of water freezing (0 ºC)
to boiling (100 ºC) of H2O
3) Fahrenheit : thermal behaviour of ice/salt/water
mixture (0 F) and his own body temperature (100 F)
Temperature measurements
Æ Material expands when heated and contracts when cooled
Outdoors/indoors: liquid (Mercury or Alcohol)
Indoor thermostat: bi-metal (copper expands faster than
steel, it causes the strip to bend Æ electrical contact)
Conversion from Fahrenheit to degrees Celsius
°C = ( F – 32 ) / 1.8
Conversion from degrees Celsius to Kelvin
Scientific: thermistor (electronic resistance)
K = °C + 273
Stevenson screen,
¾ Outdoor temperature
usually measured at 1.5-2.0 m
Barcelona, Spain
¾ Thermometer placed in a
radiation screen (a white box
with vents)
¾ Daily records at
~16000 places
worldwide
Mierij, Aanderaa & Young radiation screens
(Hock & Schroff 2004)
Temperature Lethbridge on 16-17 Sept 2012
Heat definitions
Heat Capacity (J/K)- ratio of amount of ‘heat energy’
absorbed by a substance to its corresponding temperature
rise.
Specific Heat (J/(kg·K)) - heat capacity of a unit mass of
substance = heat needed to raise the temperature of 1 kg of a
substance 1K
Sensible Heat (K or C or F)- measured by thermometer,
sensed by humans.
Latent Heat (J) - energy required to establish a phase change
or released when the change of state is reversed.
Joule= Newton per meter = m2·kg·s-2
SPECIFIC HEAT
LATENT HEAT EXCHANGE FOR 1 g OF WATER
Ratio of the amount of thermal energy absorbed (via heating) to the
corresponding rise in temperature of a unit mass of material
Substance
Specific heat
J/kg × °C
Water
Wet mud
Ice
Sandy clay
Dry air
Sand
Granite
4186
2512
2093
1381
1005
795
794
IMPORTANCE
Æ Temperature difference oceans and landmasses
1 Calorie = 4.184 Joule (= 4.184 m2·kg·s-2)
Æ Thunderstorm formation: uneven heating of ground based upon soil moisture
Temperature controls at earth surface
™ Cloud cover
™ Latitude
Earth Surface heat exchange controls
o
Albedo
o
Specific heat capacity of earth surface material (land/water)
o
Surface roughness
o
Evaporation: water surface evaporation: latent heat storage
o
Transpiration: plant surface evaporation: latent heat storage
o
Transparency: water is heat reservoir
o
Movement: mixing, ocean currents and sea-surface temperatures
™ Altitude
™ Aspect
™Type of earth surface
Maritime climate
0 m a.s.l.
Land vs. water heating differences
Continental climate
1000 m a.s.l.
July isotherms
January isotherms
warmest
coldest
coldest
warmest
Isotherms annual temperature range
Urban
microclimates
Urban Surfaces
Irregular geometric shapes
Human activity
Water does not drain
Air pollution (“Dust Dome”)
Aug
May
-40
Se pt
-40
Aug
0
May
0
Jan
+40
Se pt
+40
Jan
Marine versus continental climates
Urban compared to rural environments
™ Contaminants
WIND CHILL CHART = F(T, windspeed)
10 x more particulates/nuclei
™ Radiation
5-25% less
™ Cloudiness
5-10% more
™ Fog
30-100% more
™ Precipitation
rain: 5-15% more
snow: 5-10% less
™ Thunderstorms
10-15% more
™ Temperature
0.5-3.0°C higher
™ Relative humidity 6% less
™ Wind speed
20-30% less
HUMIDEX CHART =F(T, relative humidity)
READING for Wednesday
Chapter 3: pp. 91-103