Online Quiz

Important Terms

Circle of Illumination: Boundary separating the dark & light halves of the Earth

Earth’s Axis: Imaginary lines through the poles with Inclination 23.5°

Plane of the ecliptic: the plane of the orbit around the sun

Earth-Sun relationship

The distance between the Earth & the sun

average distance = 150 million km

Because earth orbital is ellipse the actual distance varies during year:
  – in January 147 MKm, closer to the sun
  – in July 152 MKm, Farther from the sun

The Earth has 2 principle motions

Rotation: spinning of Earth about its axis

Revolution: The earth revolves completely around the sun in an elliptical path in 365 days, Travels at nearly 113,000 km/hr

(Elliptical Orbit – Eccentricity ≈ 0.8)

Τhe Seasons

Variations distance DO NOT cause seasonal temperature change

Without the TILT we wouldn’t have seasons

The Seasons primarily due to:
1. Change in the length of daylight
2. Gradual change in angle of the sun at noon
3. amount of energy received at surface

The seasons are regulated by energy received at the surface that determined by:
1. Angle of sunlight that strikes surface:
– Overhead, perpendicularly, or directly: is more intense (or strongest intense)
– at Angle (θ) is less intense
2. how long sun shines (daylight hours): determine how warm the surface becomes

The change in day length & sun angle happens because: earth’s Rotation (earth’s orientation to sun constantly changes)

Length of Daylight & Solar Energy

During the summer in N latitudes, the sun is never very high above the horizon, so its radiant energy must pass through atm, & because of the increased cloud cover during the arctic S, much of the sunlight reflected before it reaches ground

Solar energy eventually reaches the surface in the N does not heat the surface effectively

A portion of the sun’s energy is reflected by ice & snow, while some of it melts frozen soil

The amount actually absorbed is spread over  a large area. So, even though N cities experience 24 hr of continuous sunlight on June 21, they are not warmer than cities S

Overall, they receive less radiation at the surface, & what radiation they do receive does not effectively heat the surface.

The Earth intercepts only a tiny percentage of the energy given off by the sun

Solstice & Equinoxes

Summer Solstice

– Occurs on June 21 or 22
– Tropic of CANCER (23.5°N latitud)
– Northern limit of the Sun’s rays
– First day of NH summer
– NH tilted toward the sun
– NH location experience LONGEST day
– ΝH location experience HIGHEST Sun θ
– SH location experience SHORTEST day
– SH location experience LOWEST Sun θ
– Farther from the equator → longer period of daylight (Arctic Circle has 24hr of SUN)

Winter Solstice

– Occurs on December 21 or 22
– Tropic of CAPRICORN (23.5° S)
– Southern limit of the Sun’s rays
– First day of NH winter
– NH tilted away from Sun
– NH location experience SHORTEST day
– ΝH location experience LOWEST Sun θ
– SH location experience LONGEST day
– SH location experience HIGHEST Sun θ
– Farther from the equator → longer period of daylight (Antarctic Circle has 24hr of SUN)

Equinoxes

mid way between the Solstices
– Vertical rays strike along the equator 0°
– Earth not tilted toward or away
– Autumnal Equinox: September 22 or 23
– Spring(Vernal) Equinox: March 21 or 22

Tilt

More Tilt (> 23.5°): More extreme seasons, Colder winters, & Warmer summers

Less Tilt  (<23.5): More mild seasons Cooler summers, & Milder winters

Tilt = 0 (NO TILT): No Seasons

– The location of Tropic of Cancer & Capricorn shift (Ex. 30° Tilt: tropic of Cancer 30°N & tropic of Capricorn 30°S )

– The Arctic & Antarctic circles shift 90-θ (Ex. 30° Tilt: Arctic Circle 60°N & Antarctic 60°S)

Temperature

Air T is important, Why ?

It’s the first thing we usually think when we talk about “weather”

vary on different time scales: Seasonally, daily, & hourly

vary all over the globe, by quite bit

Day Vs Night

1. On a sunny day, the air near the surface warmer than air above the surface
2. On a night, the air near the surface is colder than air above the surface

Temperature Inversion: The increase in T with increasing height above the surface (on a night)

Radiational Cooling: Radiation Inversion, Nocturnal inversions

What controls air temperature?

Differential Heating of Land & Water
Ocean Currents
Altitude
Geographic Position
Cloud Cover
Albedo

Land Vs Ocean

Differential Heating

Different surfaces absorb, emit, & reflect different amounts of energy, & This causes variations in air above each surface

Land HEATS or COOLS more rapidly so Variations over Land are GREATER

Ocean less variable, Why?
1. Surface T of water rises & falls slower
2. Water is highly mobile & mixes easily
3. Daily T changes are about 6m deep
4. Yearly ocean & deep lakes experience  variations through layer (200-660)m thick

Land are more variable, Why?
1. Heat not penetrate deeply into soil or rock & it remains near the surface
2. Rocks are not fluid… so no mixing
3. Daily T changes are 10cm down
4. Yearly T changes reach < 15m

Summer Vs Winter

During summer thick layer of water is heated while only a thin layer of land is heated

During winter the shallow layer of rock cools rapidly while the deeply heated water takes a longer time to cool

as surface water cools, becomes heavier & sinks, replaced with warmer less dense water from below, So water surface T not appear to change much

Opaque Vs Transparent

land surfaces are opaque, So heat is absorbed only at the surface

Water is transparent & lets energy from the sun penetrate to a depth of several meters

Specific Heat

amount of heat needed to raise T of 1g H₂O by 1°C (3 times greater than 1g of soil or rock) 

The OCEANS require More Reheat to raise its T same amount as an equal quantity of land

Evaporation

greater from Oceans than from Land Because There’s more water molecules (Intuitive!)

Energy is required to evaporate water: When energy is used to evaporate water it is not available for heating

WATER WARMS MORE SLOWLY THAN LAND!

Which Hemisphere (N or S) has larger T variations? & Why?

NH, there is more ocean & little land to interrupt the oceanic & atm circulation

THE END