Chapter 3
Air Temperature
Introduction
• Temperature
– the measure of sensible heat of a substance, or
– Typically measured or observed at 4 feet above
the ground surface
• Many factors affect the temperature at a
location, but there are five key factors...
Instrument Shelter
• Thermometer at 1.2 m
• Underlying surface –
grass or bare soil/dirt
• Shelter is painted
white and has “vents”
to allow air to flow
through freely
• Set up so door opens
away from Sun (on
north side in NH) –
why?
Factors Influencing Temperature
1. Insolation
– INcoming SOLar
radiATION
– affected by rotation
and revolution of Earth
Factors Influencing Temperature
2. Latitude
- in general, temperatures
decrease from equator to
poles – why?
- temps also become more
variable with increasing
latitude (seasonal
variation)
Factors Influencing Temperature
3. Surface Type
- smoothness (solar noon vs. early AM or late afternoon)
- dark vs. light-colored surface
– Urban Areas (Tucson and outside Tucson)
– (Phoenix)
4. Continentality and the marine effect
- “coastal vs. interior location” in text
- water heats/cools more slowly than land (specific heat)
– San Diego vs. Fargo
5. Elevation
- lapse rate
- greenhouse effect is less
Continentality vs. Marine Effect
Temperature Scales and
Conversion
• Three scales: Celsius, Fahrenheit, Kelvin
• Conversion formulas:
1. Celsius to Fahrenheit: 1.8 x (°C) + 32
2. Fahrenheit to Celsius: (°F – 32) ÷ 1.8
3. Celsius to Kelvin:
273.14 + °C
• 32°F/ 0°C=Freezing water
• 212°F/100°C=Boiling water
Surface Temperature
• Controlled by balance of energy flow (net
radiation of substance)
– If net radiation positive, substance heats
– If net radiation negative, substance cools
• 3 Principal ways which energy moves to/from a
surface:
– 1. Latent heat transfer (storage or release of heat due to
change of state)
• Ex: Evap. Cooling OR sweating
– 2. Conduction (flow of sensible heat via contact)
– 3. Convection (heat is distributed by rising and mixing)
Daily Cycle of Air Temperature
• _________is the main cause by the Earth which
causes significant variability in incoming solar
radiation in a 24-hour period?
– Rotation!! (Day=Positive NR, Night=Negative NR)
• In general, lows temps occur in the morning and
high temps occur in the afternoon.
• A sort of trickle-down effect from insolation to net
radiation to daily temperature
Daily Cycle of Air Temperature –
Insolation (step 1)
• Insolation begins at sunrise, peaks at solar noon,
and ends at sunset
• Daily maximum intensity and total daily insolation
vary throughout year (day length, sun angle)
Daily Cycle of Air Temperature –
Net Radiation (step 2)
• Surplus beginning just after sunrise and ending
just prior to sunset, deficit otherwise
• Magnitude and duration vary throughout year (day
length, sun angle... again!)
Daily Cycle of Air Temperature –
The End Result
• Min temp occurs around sunrise (longest period of no
insolation/negative net radiation); max occurs in mid-afternoon
(convection causes mixing of warm/cool air)
• So... insolation and net radiation affect daily temp cycle (ignoring
other conditions like cloudiness, fronts, precipitation, etc.)
Human Activity and Temperature
• How do humans impact temperature?
1. Removal of vegetation – less cooling via
transpiration/evapotranspiration
2. Pavement – conduct and hold heat
3. Structures – more absorption; more reflection
by vertical surfaces
4. Fuel consumption/exhaust – a/c
5. Greenhouse gases (mostly long-term)
• # 1 – 4 lead to development of urban heat island
What’s an Urban Heat Island?
• Warmer area surrounding city due to less
vegetation, building structure/components,
pavement, and fuel consumption/exhaust
• Noticeable in both high and low temperatures
• Does Tucson have one?
Rural vs. Urban Climate Warming
Vertical Temperature Structure of
the Atmosphere
• With an increase in altitude, temperature
can:
1. Lapse rate: temp decrease with height
• MOST COMMON
2. Inversion: temp increase with height
3. Isothermal layer: no temp change
Vertical Temperature Structure of
the Atmosphere – Lapse Rate
• Lapse rate not always the same, but varies
with humidity and temperature and moisture
advection
• Measures the drop in temperature in degrees
Celsius per 1,000m
• Just an average rate (6.5°C/1,000m)
Vertical Temperature Structure of
the Atmosphere
• Thermosphere
– Upper layer, temp increases with height
– Location of auroras (interaction of ions and radiation)
• Mesosphere
– 3rd layer, temp decreases with height until mesopause
– Lowest average temperatures in atmosphere (-90°C)
• Stratosphere
– Next layer, strong ozone presence
– Temp increases with altitude until stratopause
• Troposphere
– Lowest layer, where most weather phenomena occur
– Temp decreases with altitude until tropopause
Vertical Temperature Structure of
the Atmosphere
Annual Cycle of Air Temperature
•
•
Revolution and tilt of axis  variations in day length 
insolation variation  cycle of net radiation  cycle of
mean (average) monthly temperatures
Also affected by:
1. Elevation
2. Latitude
3. Continentality vs. marine effect
4. Albedo
World Temperature Characteristics
• Common practice is to analyze January and July
temperature – why?
• Study both spatial and temporal patterns
• Isotherms-lines that are drawn on a map to
connect locations having the same temperature
– World patterns of isotherms
• 1. Latitude
• 2. Coast/Interior
• 3. Elevation
Spatial Temperature Patterns
• General decrease with increasing latitude (large
annual insolation variation)
• Large land masses in high latitudes get VERY
COLD (snow cover  high albedo)
• Little change in equatorial regions (small annual
insolation variation)
• Large north-south shift in isotherms over land, less
over oceans (continentality, marine effect)
• High-elevations cold vs low elevations (lapse rate)
• Perpetually ice- and snow-covered regions always
much colder than elsewhere (high elevation, high
albedo)
Spatial Temperature Patterns
Temporal Temperature Patterns
• Annual range increases with latitude (insolation
variations)
• Largest annual ranges over arctic/sub-arctic zones
of Asia and North Am. (insolation)
• Moderately large ranges over tropical deserts
(continentality)
• At same latitude, annual range over ocean less
than over land (marine effect)
• Annual range very low over tropical oceans (little
annual insolation variation, marine effect)
Temporal Temperature Patterns
Temporal Temperature Patterns
Climate Change Studies
• Ice cores and tree-ring growth
• Climate modeling: “popular” technique is study of
increasing (usually doubling) CO2
• Intergovernmental Panel on Climate Change (IPCC)
– 1995: “climate warming due to human activity”
– 2001: global mean temp ↑, snow/ice cover ↓, global mean sea
level ↑, greenhouse gas concentrations ↑, cloud cover/precip
↑ in mid-latitudes of NH
• Kyoto Protocol
- 1997: 38 industrial nations agree to ↓ greenhouse gas
emissions to ~5% below 1990 levels
- 1998: implementation of 1999-2000 reductions, emission
trades, developing countries join
- 2001: W rejects US participation, but 178 new nations