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Unit 2: Patterns in Weather and Climate Chapter 4: Weather and Climate Weather: daily atmospheric condition (heat, moisture, air movement) for a given area. Climate: average weather conditions over an extended period of time. The Three Main Factors that Affect both Weather and Climate: 1. Temperature. 2. Moisture. 3. Air Movement. Earth’s warmth is derived from the sun’s energy – INcoming SOlar radiATION or INSOLATION. The Earth’s surface does not receive direct sun rays. WHY???? Our atmosphere filters much of the insolation: 30% reflected to atmosphere. 17% absorbed by the air. 53% reaches the ground. 1 Of the radiation reaching the ground some is absorbed and some is reflected. Snow and Ice REFLECT. Water, vegetation, dark ground ABSORB. The Greenhouse Effect: 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. 2 The Earth – Sun Relationship: 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 Counterclockwise 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 counterclockwise 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. The Earth’s axis is tilted 23.5o from the vertical. This tilt is continuous during Earth’s revolution. This is why we have SEASONS in the higher latitudes. 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. 3 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. At 2 times during the year the number of day and nights hours is equal. - called EQUINOXES (equal night) MARCH 21 is the VERNAL (SPRING) EQUINOX. SEPT 22/23 is the AUTUMNAL EQUINOX. These dates mark the 1st day of Spring and Fall, respectively, in the Northern Hemisphere. 0o latitude is the EQUATOR. 23.5oN is the TROPIC of CANCER. 23.5oS is the TROPIC of CAPRICORN. 4 In Northern Hemisphere, the sun is directly overhead at noon on JUNE 21 at 23.5oN. Longest day of the year. 1st day of SUMMER is called the SUMMER SOLSTICE. On Dec 22nd, the sun is directly overhead at noon at 23.5oS. In the Northern Hemisphere, this is the shortest day of the year. The beginning of WINTER, it is known as the WINTER SOLSTICE. Pattern in Temperature (Latitude): The Earth’s curvature causes the sun’s heat to be unevenly distributed. 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. Other Factors Affecting Climate: 1. Winds: The horizontal movement of air. Occur to equalize varying pressure within atmosphere. Air moves from HIGH PRESSURE to LOW PRESSURE (Always). 5 There are major pressure belts over the globe: Winds are named according to the DIRECTION from which they blow. (Note: Coriolis Effect) Winds, as a result, influence temperatures. They also influence moisture levels. Wind’s Impact on Moisture: A. Orographic Rainfall: Caused by abrupt changes in relief, air masses rise up mountains. Air is forced to rise because it is deflected upward by the high mountains. As the air rises, it cools and its ability to hold moisture lessens (condensation occurs). 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. The air begins to descend down the inland (leeward) side of the mountain, it compresses and becomes warmer. The relative humidity of the air lowers, having a drying effect. 6 Rain Shadow – is an area of relatively low rainfall on the leeward side of the uplands. Refer to figure 4.13 on page 66. B. Frontal Rainfall: Occurs when a FRONT is created on the meeting of two air masses with different temperatures. As a warm air comes in contact with colder air, it is forced to rise up over the colder air because the colder air is denser and heavier than the warm air. As the warm air rises, it becomes cooler. As the warm air cools, the relative humidity rises, to the point at which the air masses can no longer hold the water vapour it brought from the ocean. This water vapour condenses and falls as precipitation. Refer to figure 4.14 on page 66. C. Convectional Rainfall: Not related to wind. Results from RAPID uplift of air due to intense HEATING. Common along the equator. 7 This type of precipitation typically occurs in the summer in mid-to late afternoon after a day of high rising temperature. Lightning and thunder often accompany this type of precipitation because the air flows quite rapidly and intensely. Which cause considerable friction between the air molecules. Refer to figure 4.15 on page 67. 2. Nearness of Land to Water: Land masses heat up and cool down more RAPIDLY than water. Areas near the water often experience 2 types of BREEZES: A. Land Breeze: 8 Sea Breeze: 3. Ocean Currents: Refer to map on page 60. Currents (movements of large amounts of ocean water) result from unequal heating of the top layer of water by the sun. Generally there is a circular flow of dense cold water of Polar Regions to displace the less dense warmer water equatorial zones. This equator ward flow is complicated by: i. ii. iii. iv. Winds Shorelines Shape of continents Earth’s rotation 9 Influence on Weather/Climate: Warmer currents (Gulf Stream, Japan Current (or Kuroshio) tend to modify or moderate temps of cooler areas into which they flow. Ex: European weather warmed by Gulf Stream. Ex: B.C. coast warmed by the Kuroshio Current. Colder currents (Labrador, Peru Current) have a cooling effect. These currents cool the air above which causes the air to have less capacity for holding moisture. This results in generally lower precipitation levels for these areas. Where warm and cold ocean currents meet FOG is produced. Ex: Grand Banks off NL meeting place of Gulf Stream and Labrador Current = Heavy Fog. 4. Elevation of the Land: General rule: the HIGHER the elevation, the LOWER the temperature. Before condensation occurs 1oC decrease for every 100 m increase. After condensation occurs 0.6oC decrease for every 100 m increase. 10 Monsoons: Occur because of differences in heating over the interior of the Asian continent and the Indian Ocean during different seasons. In the winter, central Asia is very cold and an area of high pressure develops over the area. Strong winds blow from this high pressure towards lower pressure over the Indian Ocean. In the summer, the reverse takes place because the Asian interior becomes very hot and a large low – pressure area develops. Strong moisture – laden winds blow from high pressure over the Indian Ocean towards the Asian and Indian Continent. Dry Monsoons from Sept. – March. Wet Monsoons from June – Sept. 11