Chapter 3. Why the Earth has seasons Earth revolves in elliptical path around sun every 365 days. ...
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Transcript of Chapter 3. Why the Earth has seasons Earth revolves in elliptical path around sun every 365 days. ...
Chapter 3
Why the Earth has seasons Earth revolves in elliptical path around
sun every 365 days. Earth rotates counterclockwise or
eastward every 24 hours. Earth closest to Sun (147 million km) in
January, farthest from Sun (152 million lm) in July.
Distance not the only factor impacting seasons.
Why the Earth has seasons The amount of energy that reaches the
Earths surface is influence by the distance from the Sun, the solar angle, and the length of daylight.
When the Earth tilts toward the sun in summer, higher solar angles and longer days equate to high temperatures.
Why the Earth has seasons Seasons in the Northern Hemisphere
Summer solstice: June 21, Sun directly above Tropic of Cancer, Northern Hemisphere days greater than 12 hours
Winter solstice: December 21, Sun directly above Tropic of Capricorn, Northern Hemisphere days less than 12 hours
Autumnal and Spring Equinox: September 22, Marc 20, Sun directly above Equator, all locations have a 12 hour day
Stepped Art
Fig. 3-8, p. 63
Why the Earth has seasons Special Topic: First day of winter
December 21 is the astronomical first day of winter, sun passes over the Tropic of Capricorn; not based on temperature.
Why the Earth has seasons Seasons in the Southern Hemisphere
Opposite timing of Northern HemisphereCloser to sun in summer but not significant
difference from north due to:○ Greater amount of water absorbing heat○ Shorter season
Simplified Surface Energy Balance
NET R = + SW (insolation) – SW (reflection) + LW (infrared) – LW (infrared)
Figure 3.13
Local temperature variations Southern exposure: warmer, drier
locations facing south. Implications forVegetationVinicultureSki slopesLandscapingArchitecture
Local temperature variations Environmental Issues: Solar Heating
In order to collect enough energy from solar power to heat a house, the roof should be perpendicular to the winter sun.
For the mid-latitudes the roof slant should be 45°- 50°
Daily temperature variations Each day like a tiny season with a cycle
of heating and cooling Daytime heating
Air poor conductor so initial heating only effects air next to ground
As energy builds convection begins and heats higher portions of the atmosphere
After atmosphere heats from convection high temperature 3-5PM; lag in temperature
Daily temperature variations Properties of soil affect the rate of
conduction from Earth to atmosphere Wind mixes energy into air column and
can force convection.
Daily temperature variations Nighttime cooling
As sun lowers, the lower solar angle causes insolation to be spread across a larger area
Radiational cooling as infrared energy is emitted by the Earth’s surface
Radiation inversion: air near ground much cooler than air above
Thermal belt
Stepped Art
Fig. 3-14, p. 69
Daily temperature variations Protecting crops from cold
CoverSmudge potsFansSprinklers
The controls of temperature Latitude: solar angle and day length Land & water: specific heat Ocean currents: warm and cold currents Elevation: cooling and increase range
Land–Water Heating Differences Evaporation
Transparency Specific heat Movement Ocean currents and sea surface
temperatures Marine vs. continental effects
Land–Water Heating Differences
Figure 3.20
Global Temperature Ranges
Figure 3.28
Air temperature data
Daily, monthly, yearly temperatureRange: maximum minus minimumMean: average of temperature observationsMaximum: highest temperature of time
periodMinimum: lowest temperature of time period
Air temperature data
Special topic: What’s normal?Climate normal is the 30 year average for a
given temperature variable.
Air temperature data
The use of temperature dataHeating degree-day: people heat when
temperature below 65°FCooling degree-day: people cool when
temperature above 65°FGrowing degree-day: temperature above of
below base temperature for specific crop
Air temperature and human comfort Body heats through metabolism
wind-chill indexHypothermia
Body cools through emitting infrared energy and evaporation of perspiration
Wind Chill Table
Figure 1
Heat Index Table
Figure 2
Air temperature and human comfort Observation: 1000 degrees
Thin air at the top of the atmosphere does not have enough molecules to create a high temperature as measured by a thermometer.
The Urban Environment
Figure 3.29
Measuring air temperature Thermometers: liquid-in-glass,
maximum, minimum, electrical resistance, bimetallic
ASOS Thermistors Infrared sensors
Urban Heat Island
Figure 3.30
Measuring air temperature Observation: Thermometers in the
shadeRadiant energy from the Sun in direct
sunlight increases the temperature recorded by a sensor.
True air temperature measured in the shade.