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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

2

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

3

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

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Temperature varies horizontally

• Based on insolation and continentality

Horizontal variation in temperature

0º40º

Winter

Summer

Winter

Summer

Horizontal variation in temperatureAverage sea level temperature °F in July