Chapter 4: Weather & Climate (Pg. 54 73)
Introduction:
Distinguish between the terms weather & climate. P. 54 Weather: the state of the atmosphere at any one place or time. (short term) Climate: the average weather conditions of a region over the LONG term. (Season, Month Annually) Both refer to temperature, rain fall, humidity etc.
Practice: Do the following phrases refer to weather or climate? 1. Annual precipitation of 200 mm. 2. Rain forecasted for tomorrow. 3. Normal July temperature averages 22 o C. 4. Temperatures this week will range between 20-30 o C. 5. It was unusually hot this summer. 6. Vancouver has an annual frost free period of 233 days. 7. The greatest annual precipitation 11, 680 mm falls on Mt. Waialeaie in Hawaii. 8. Residents in Florida are preparing to take shelter from a hurricane. Climate Weather Climate Weather Climate Climate Climate Weather
In describing today s weather: 9 features are often used!! 1. Temperature 2. Amount of precipitation 3. Type of precipitation 4. Atmospheric pressure 5. Wind direction 6. Wind speed 7. Cloud cover 8. Hours of sunshine 9. Humidity
How does cloud cover influence the range of temperatures from day to night. (2.1.2) Nightly cloud cover reduces the range of temperature from day to night. Clouds reflect heat waves Heat below clouds is reflected back to earth. Without clouds heat escapes giving colder nights.
Lack of cloud cover Day AND Night the effect DAY: No clouds = higher day temperatures Why? NO clouds to deflect/block heat from reaching the surface. NIGHT: No cloud cover = cold nightly temperatures. Why? Heat escapes, nothing to TRAP it. Ex. Day 24 o C, Night 15 o C
Clear Day AND clouds over BEFORE night the effect DAY: No clouds = higher day temperatures Why? NO clouds to deflect/block heat from reaching the surface. Cloud cover PRIOR to night = = warmer and muggy nights. Why? Heat being TRAPPED during the night like a blanket AND precipitation in the clouds. Ex. Day 24 o C, Night 21 o C
Cloudy Day AND NO clouds at Night the effect DAY: Cloud cover = lower daily temperatures Clouds deflect/block out sun & heat. NIGHT: NO cloud cover =even COLDER nightly temperatures. Already cooler temperatures become even lower. Ex. Day 15 o C, Night 9 o C
Cloudy Day AND cloudy Night the effect Day: Cloud cover = lower daily temperatures Why? Clouds deflects/blocks out heat Night: Cloud cover = relatively constant temperatures in the night. Why? Clouds traps current air temperatures and keeps them relatively constant. Ex. Day 15 o C, Night 12 o C
So.. Clear day/clear Night: largest temp range (24 15=9) Clear day, cloudy night: small/low temp range (24-21=3) Cloudy day, clear night: moderate range (15-9=6) Cloudy day/cloudy night: small temp range(15-12=3)
Why does only about ½ of the sunlight directed at earth actually reaches the earth?
49% of sun s radiation actually reaches the earth s surface (pg. 57) 6% is scattered in the atmosphere 24 % is reflected by clouds 4 % is reflected by the earth s surface. 17 % is absorbed by Green House gases & dust
While the 4 % that reflects from the earth s surface is small it does vary with location & with time. How/Why do you think it varies? Winter vs. Summer? Poles Vs. equator? Land vs. ocean? HINT: Precipitation (Snow & water), reflection vs absorption, dust, cloud cover, angle of sun,
The Greenhouse Effect: (2.2.1) The Earth system behaves like a greenhouse. The atmosphere, like the glass/plastic of a greenhouse traps heat energy resulted increased temps.
SHORT WAVE insolation reaches the ground and is absorbed. The Earth heats up and gives off LONG WAVE terrestrial radiation which is absorbed by the atmosphere causing it to heat up.
The Earth Sun Relationship: (2.1.1, 2.1.4, 2.1.5 & 2.1.6) Because the Earth is a sphere, all areas on the planet do not receive the same intensity insolation. The Earth ROTATES on its axis toward EAST or counter clockwise when looking down from the North Pole. It takes the Earth 24 HOURS to make 1 complete rotation on its axis. Earth REVOLVES around the sun counter clockwise looking down from the North.
It takes 365.25 days to make 1 complete REVOLUTION. This is why we have a LEAP YEAR every 4 years. This keeps our calendar in sync with the Earth s revolution. SEE FIGURE ON PAGE 56 IN TEXT.
Tilt of the Earth: The earth is tilted on its axis 23.5 o At different times of the year, the North (or South) is pointed towards the sun, while other times pointed away from the sun. Causes daylight to be longer or shorter. Contributes to the seasons as well.
During part of the revolution, the North Pole is tilting away from the sun. At another time, the North Pole is tilted toward the sun. Titling toward and away from the sun affects the intensity of the insolation.
As we tilt AWAY from the sun, insolation is less intense and we in the Northern Hemisphere experience cooler temps. (our WINTER) During our summer, the Northern Hemisphere tilts TOWARD the sun resulting in more intense radiation. SEE FIGURE 4.3 PAGE 56. (Magnifying Glass) The tilt of the axis also results in the length of DAYLIGHT and NIGHTTIME varying throughout the year.
Day vs Night & Length of day (daylight!) Rotation on the axis causes day and night. Tilt on axis causes length of day to be longer or shorter. When hemisphere is pointed towards the sun that hemisphere receives more direct, intense heat radiation AND More hours of exposure to the sun Giving that hemisphere longer days AND Warmer temperatures (Summer!!)
Equal Day and Night BUT Differences in Temperatures!? Why?
Intensity and Duration!!
Equinoxes vs. Solstices (2.1.3)
Equinoxes: At 2 times during the year the number of day and nights hours is equal. (equal night) MARCH 21 is the VERNAL (SPRING) EQUINOX. SEPT 22/23 is the AUTUMNAL EQUINOX. These dates mark the 1 st day of Spring and Fall, respectively, in the Northern Hemisphere.
Solstices: In Northern Hemisphere, the sun is directly overhead at noon on JUNE 21 at 23.5 o N. (Longest day of the year.) 1 st day of SUMMER is called the SUMMER SOLSTICE. On Dec 22 nd, the sun is directly overhead at noon at 23.5 o S. In the Northern Hemisphere, this is the shortest day of the year. The beginning of WINTER, it is known as the WINTER SOLSTICE.
Season changes (2.1.4) Seasonal changes are all driven by changes in: The tilt of the earth on its axis AND The position of the earth in its revolution around the sun NOTE: These will ultimately determine: the amount of available sunlight (called day length or photoperiod) the sun's intensity (related to the angle at which it strikes the Earth). Warmer vs cooler
Seasons Summary: SUMMER in the NORTH!! A June 21 st or 22 nd. North = Summer More sun hours More direct sun Noon Sun 90 0 @ Tropic of Cancer South = Winter Less sun hours Less direct sun
Seasons Summary: FALL / AUTUMN in the NORTH September 21 st North = Fall 12 hrs day & 12 hrs night Noon Sun 90 0 @ Equator South = Spring B A
Seasons Summary: WINTER in the NORTH Dec 21 st North = Winter Less sun hours Less direct sun South = Summer More sun hours More direct sun Noon Sun 90 0 @ Tropic of Capricorn C B A
Seasons Summary: SPRING in the NORTH March 21 st North = Spring 12 hrs day & 12 hrs night Noon Sun 90 0 @ Equator South = Fall C B A D
Seasons Summary Back to Summer AGAIN B
SEASONS??? NORTH DATE??? EQUINOX/SOLSTICE? SOUTH NORTH SOUTH
Seasons animated: Sun s Angle and Intensity Seasons and Ecliptic Simulator
Factors that Affect Climate
1. Earth-Sun Relationship
2. Latitude: (Obj.2.2.1 & 2.2.3) 0 The Earth s curvature causes the sun s heat to be unevenly distributed. 0 When the Sun s rays strike the Earth s spherical body, the region that corresponds to the equator receives more radiation than the region corresponding to the poles. 0 The HIGHER the latitude (Northern/Southern Hemisphere) the COLDER it gets.
Intensity and Duration!!
3. Winds: (Obj. 2.3.1, 2.3.3, 2.3.4, & 2.3.5) 0 Wind: is the flow of air from an area of high pressure to one of low pressure 0 Prevailing Winds: is the major, constant winds blowing over the surface of Earth from high to low pressure areas. 0 Air moves from HIGH PRESSURE to LOW PRESSURE (Always).
0 There are major pressure belts over the globe:
There are three major wind systems: 0 Trade Winds, Westerlies and Polar Easterlies. 0 Each of the three systems relate to the major pressure belts: 1. Trade winds flow from the tropical high to the equatorial lows 2. The Easterlies from the polar highs to the subpolar lows 3. The Westerlies from the tropical highs to the subpolar lows.
0 Winds are named according to the DIRECTION from which they blow. (Note: Coriolis Effect) 0 Winds, as a result, influence temperatures. 0 They also influence moisture levels.
Coriolis Force:
0 Coriolis Force: is the tendency for objects or fluids to be deflected to the RIGHT of their path in the Northern Hemisphere and to the LEFT in the Southern Hemisphere; caused by the rotation of the earth. 0 The effect of the Coriolis Force is negligible at the equator but increases in intensity towards the poles.
Animation of the Coriolis effect over Earth's surface
Wind s Impact on Moisture: (Obj. 2.3.5, 2.3.6, & 2.3.7)
A. Orographic Rainfall: 0 Caused by abrupt changes in relief, air masses rise up mountains. 0 Air is forced to rise (WINDWARD)because it is deflected upward by the high mountains. 0 As the air rises, it cools and its ability to hold moisture lessens (condensation occurs).
0 By the time the air reaches the highest point on the mountain, it has lost most of its water vapour it picked dup over the ocean. 0 The air begins to descend down the inland (LEEWARD) side of the mountain, it compresses and becomes warmer. 0 The relative humidity of the air lowers, having a drying effect.
0 RAIN SHADOW: is an area of relatively low rainfall on the leeward side of the uplands. 0 Refer to figure 4.13 on page 66.