Insolation and
Temperature variation
Atmosphere: blanket of air surrounding earth
1.
2.
3.
Without our atmosphere: cold, quiet, cratered place
Dynamic: currents and circulation cells
June 23, 2008
Atmosphere important in equalizing temperature
and pressure by transfer of ____________,
______________, and ______________________
Meteorology...the study of weather
condition of atmosphere at a given time for a given area
temperature, pressure, wind, moisture
Climatology...the study of long term average weather
usually over past 30 years
The Sun & Insolation
The Sun
The Sun (cont.)
• Provides an immense and continuous flow
of radiant energy
– Electromagnetic waves
• Uv, visible, infrared
• Almost all is shortwave (uv & visible)
• Dispersed in all directions
• Less than one billionth of total solar
output reaches Earth’s atmosphere
1
Driving force behind weather and climate
How bright the sun shines
Factors affecting intensity
1.
Total insolation is a function of __________________
Controlled primarily by ____________
1.
affects intensity of insolation
Latitudinal comparison
Angle of
incidence
Surface area
covered
(Latitude and season affect angle of sun’s rays)
2.
affects intensity of insolation
How bright the sun shines
Factors affecting intensity
1.
2.
2
100% at top of
atmosphere
How bright the sun shines
5% scattered
or reflected
30-60% reflected by
clouds
Factors affecting intensity
1.
15% absorbed
by molecules
and dust
2.
3.
5-20% absorbed
by clouds
80% can reach
ground on
clear day
0-45% reaches ground
on cloudy day
3.
affects intensity of insolation
Mt. Everest, 5.5 mi high
How long the sun shines during the day
Depends on _____________ and ________________
High-latitudes
Duration of Insolation
N.Pole
Spring June
Fall
December
Equinox Solstice Equinox Solstice
12 hrs. 24 hrs.
12 hrs.
0 hrs.
N.Mid-Lat 12 hrs.
~15 hrs
12 hrs.
~9 hrs.
Equator
12 hrs.
12 hrs.
12 hrs.
12 hrs.
S.Mid-lat 12 hrs.
~9 hrs.
12 hrs.
~15 hrs
S. Pole
12 hrs.
0 hrs.
12 hrs.
24 hrs.
Mid-latitudes: sun never
directly overhead
Tropics: sun is directly
overhead twice a year
Low latitudes
Jun
Equinoxes
De
Mid-latitudes: sun never
directly overhead
e
cem
be
r
High-latitudes
3
TROPICS: insolation high year round
due to high sun angle and constant
duration
Mid-latitudes: insolation highest at
summer solstice due to higher sun angle
and longer day, lowest at winter solstice
due to low angle and short day
High latitudes: insolation highest at
summer solstice due to 24 hour duration
low angle sun, extremely low to none at
winter solstice
Seasonal variation in insolation at top of atmosphere
Equator
Duration
Poles
Angle
Total
Duration Angle
Total
Spring
12 hrs.
Equinox
High
High
12 hrs.
Horizon
Low
Sum.
12 hrs.
Solstice
High-
High-
24 hrs
Low
High
Fall
12 hrs.
Equinox
High
High
12 hrs.
Horizon
Low
Winter
12 hrs.
Solstice
High-
High-
0 hrs.
Below
horizon
Zero
Insolation that reaches the Earth can be…
Total annual insolation decreases as latitude
increases
Seasonality increases as latitude increases
High albedo
Absorbed radiation heats the earth. The earth then
radiates energy back out.
Earth radiates in longer wavelengths
90% of this radiation absorbed by atmosphere
Low albedo
Earth’s energy balance
• There is a balance between the total
amount of insolation received by Earth &
atmosphere & total amount radiation
returned to space
Clouds also absorb outgoing longwave energy
Atmosphere is warm, therefore it also radiates energy
Counter radiation directed back to Earth
4
Net Radiation
Global average energy balance
Surplus
• Incoming – Outgoing radiation energy
Deficit
Tropics
• Highest at low latitudes = surplus energy
• Lowest at high latitudes = deficit of energy
Mid-High latitudes
San Francisco
St. Louis
Washington DC
How does heat move from one
place to another?
How can earth move energy from surplus to
deficit areas? (Methods of heat transfer)
1.
All bodies above -460°F (-273°C) (0° Kelvin) radiate
energy.
1.
2.
3.
Lower body temperature, longer wavelength.
Thermal infrared wavelength energy radiated by Earth
heats troposphere.
• 2.
• Heat that is transferred from one part of a stationary
body to another when the two are in contact
• Earth-air interface
3.
• Heat transferred from one point to another
by a moving substance
– Land heats up – transferred to lower atmosphere
ConvectionVertical currents
AdvectionHorizontal currents
For this – only important at earth-air
interface
5
Temperature
• Measurement of sensible heat/energy
• Temperature is an expression of the
degree of hotness or coldness of a
substance
• There is a link between troposphere
temperature and Earth surface conditions
– The air temperature represents the balance
between insolation and terrestrial radiation
Temperature depends on …
Temperature Depends On …
2.
1.
Intensity
x
Duration
angle of sun’s rays
latitude
atmospheric
transparency
season
altitude
Temperature depends on …
Relative rates of heat flow into soil and water
3.
Most land has low albedo. It absorbs radiation and heats up
6
Relative rates of heat flow into soil and water
Why does water heat and cool
slower than land?
Soil
5°C
10°C
20°C
40°C
1.
2.
3.
4.
5.
Water heats up (and cools down) slower than land Æ
CONTINENTALITY
Temporal variation in temperature
1990 Daily temperature ranges
Minneapolis-St.Paul
•
•
•
Freezing
Summer Solstice
Winter Solstice
Temperature Varies
Lapse Rate
• Rate at which temperature decreases with
height
Temperature varies
vertically. In the
troposphere, it usually
gets colder as you go
up.
This normal change in
temprature is called
the “normal” or
“environmental” lapse
(change) rate.
7
Horizontal variation in temperature
Temperature varies horizontally
Winter
• Based on insolation and continentality
40º
0º
Summer
Horizontal variation in temperature
Average sea level temperature °F in July
Summer
Winter
8