atmosphere: blanket of air surrounding earth insolation ... · atmosphere: blanket of air...
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Insolation and Temperature variation
June 23, 2008
Atmosphere: blanket of air surrounding earth1. 2. 3.
Without our atmosphere: cold, quiet, cratered place
Dynamic: currents and circulation cells
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
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Driving force behind weather and climate
Total insolation is a function of __________________
Controlled primarily by ____________
How bright the sun shines
Factors affecting intensity
1.
1. affects intensity of insolation
(Latitude and season affect angle of sun’s rays)
Latitudinal comparison Angle of incidence Surface area
covered
How bright the sun shines
Factors affecting intensity
1.
2.
2. affects intensity of insolation
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100% at top of atmosphere
80% can reach ground on clear day
15% absorbed by molecules and dust
5% scattered or reflected
0-45% reaches ground on cloudy day
5-20% absorbed by clouds
30-60% reflected by clouds
How bright the sun shines
Factors affecting intensity
1.
2.
3.
3. affects intensity of insolation
Mt. Everest, 5.5 mi high
How long the sun shines during the day
Depends on _____________ and ________________
~15 hrs12 hrs.~9 hrs.12 hrs.S.Mid-lat
24 hrs.12 hrs.0 hrs.12 hrs.S. Pole
12 hrs.12 hrs.12 hrs.12 hrs.Equator
~9 hrs.12 hrs.~15 hrs12 hrs.N.Mid-Lat
0 hrs.12 hrs.24 hrs.12 hrs.N.Pole
December Solstice
Fall Equinox
June Solstice
SpringEquinox
Duration of Insolation
Equinoxes
June
December
Tropics: sun is directly overhead twice a year
Low latitudes
Mid-latitudes: sun never directly overhead
Mid-latitudes: sun never directly overhead
High-latitudes
High-latitudes
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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
Belowhorizon
Horizon
Low
Horizon
Angle
PolesEquator
High-
High
High-
High
Angle
Zero0 hrs.High-12 hrs.WinterSolstice
Low12 hrs.High12 hrs.Fall Equinox
High24 hrsHigh-12 hrs.Sum. Solstice
Low12 hrs.High12 hrs.Spring Equinox
TotalDurationTotalDuration
Seasonal variation in insolation at top of atmosphere
Total annual insolation decreases as latitude increases
Seasonality increases as latitude increases
Insolation that reaches the Earth can be…
High albedo Low albedo
Earth radiates in longer wavelengths90% of this radiation absorbed by atmosphere
Clouds also absorb outgoing longwave energy
Atmosphere is warm, therefore it also radiates energy
Counter radiation directed back to Earth
Absorbed radiation heats the earth. The earth then radiates energy back out.
Earth’s energy balance
• There is a balance between the total amount of insolation received by Earth & atmosphere & total amount radiation returned to space
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Net Radiation
• Incoming – Outgoing radiation energy
• Highest at low latitudes = surplus energy• Lowest at high latitudes = deficit of energy
Global average energy balance
Surplus
DeficitTropics
Mid-High latitudes
San FranciscoSt. LouisWashington DC
How does heat move from one place to another?
1.2.3.
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.
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
– Land heats up – transferred to lower atmosphere
For this – only important at earth-air interface
3. • Heat transferred from one point to another
by a moving substance
Convection-Vertical currents
Advection-Horizontal currents
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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 …
1.
altitude
seasonatmospheric transparency
latitudeangle of sun’s rays
Intensity x Duration
Temperature depends on …
2.
Temperature depends on …
3. Relative rates of heat flow into soil and water
Most land has low albedo. It absorbs radiation and heats up
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Relative rates of heat flow into soil and water
Soil 5°C 10°C 20°C 40°C
Water heats up (and cools down) slower than land
CONTINENTALITY
Why does water heat and cool slower than land?
1.2.3.4.5.
Temperature Varies
•••
Temporal variation in temperature
Freezing
1990 Daily temperature rangesMinneapolis-St.Paul
Sum
mer
Sol
stic
e
Win
ter S
olst
ice
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.
Lapse Rate
• Rate at which temperature decreases with height