Due to the Coriolis effect, prevailing winds are: 0-30 N - trade winds (trade winds blow toward the equator) N N - (fig 14.

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1 1 CD2 Factors that Influence the Earth s Climate Meteorology Meteorology is the study of the Earth's atmosphere and weather systems. The atmosphere is the layer of gases that surround the Earth which extends to an altitude of about km. Weather occurs in the troposphere, (up to about km) and is defined as the sum of the atmospheric conditions in a given place at a given time. (fig 13.14, p442) The Causes of Weather: Heat and Energy Transfer Weather is caused by. Because the Earth is spherical, rotating, and varied in composition, some areas receive and store much of the sun's energy, while other areas receive little. In general, the Earth's surface will absorb about 50% of the solar radiation that enters the atmosphere. The other half is absorbed by the atmosphere (20%) or reflected by clouds and ground (30%). (fig 13.4, p424) Snow and clouds have high albedo values (~0.8 or 80 %) and are very effective in reflecting the sun's radiation. The albedo effect (reflecting the sun's energy) lessens heating of the Earth's surface, and can also influence weather. Rays of light that are perpendicular to the surface on which they shine provide much more heat than rays at a shallow angle. (fig 13.3, p424) When the rays are perpendicular, such as it is at the equator, the Sun delivers 1367 J/m 2 s. Near the poles, this number is significantly less. Different substances have different abilities to hold heat, or. Compare the heat capacities of sand (295 J/kg C) with that of water (4186 J/kg C). Because water has such a high heat capacity, it takes regions near water longer to heat up or cool off. The water cycle has a large effect on weather, as water is the principle mechanism for heat transfer. (fig 13.10, p434) The fact that the Earth is means that at any given time, half of the Earth is being heated, (unevenly), and the other half is being cooled. (also unevenly) This difference in energy distribution is the cause of virtually all weather phenomena. Seasons are caused by the of the Earth's rotational with respect to its plane of orbit. The Earth currently maintains a tilt from its plane, which means that when the northern hemisphere is tilted towards the sun, it receives more direct light for longer. This is our summer. During the winter, we are tilted from the sun, receiving less intense light for less time. The equator would receive close to the same amount of light, with the same intensity all year, and would thus not experience seasons the way we do. (fig 14.5, p456) Important Lines is a measure of the distance north or south from the equator. The equator is set to 0 and the poles are 90 N and 90 S. is a measure of the distance east or west from the meridian, an imaginary line that runs from pole to pole through Greenwich, England. (0 ) On the other side of the world is the International Date Line (180 ), and distances are designated east or west as if observing from off the Earth. Using these lines, you can locate any point on Earth. (fig 14.2, p454)

2 2 The Arctic/Antarctic circles are from their respective poles and mark the polar zones. These lines also mark the regions where there is 24 light or darkness at the solstices (June 21 and Dec. 21). The Tropic of and the Tropic of are 23.5 north and south of the equator respectively. These mark the boundaries between the temperate zones and the central tropical zone. (p460) Wind Wind is caused by the mixing of air. Because warm air is less dense than cool air, it rises, and vice versa. Cool, dense air exerts pressure on warmer air and pushes it up, out of the way. When the warm air rises, it expands, cools, and falls back to the ground. This creates a circulatory movement of a mass of air, caused by temperature difference and hence density. This is called. (fig 13.13, p441) Prevailing Winds and the Coriolis Effect Convection occurs on a global scale. If the Earth were a smaller sphere, the warm air near the equator would rise, and the cold dense air from the poles would rush in to replace it. This would cause winds in the northern hemisphere. (fig 14.8, p462) However, because the Earth is so large, by the time the warm air from the equator reaches 30 N, it has cooled so much, it falls to the ground. Some returns to the equator, and some is pushed north. Meanwhile, cold air from the north is heated and by 60 N, it rises. This causes 3 distinct patterns: 0-30 N - northerly, N - southerly, N - northerly. (fig 14.8, p463) Because of the of the Earth, if air were not moving with it, you would feel a constant wind of about 1000 km/h. You don't, therefore in general, the air molecules rotate with the Earth. The molecules are moving faster at 30 than 60 N. As the southerly convection current pushes the air north, the air that was moving east at 30 will move faster than the air at 60 N. This difference is felt as wind. We call a prevailing wind moving from west to east - westerly. This change in the motion of moving objects on the surface of a rotating body is called the effect. (fig 14.10, p464) Due to the Coriolis effect, prevailing winds are: 0-30 N - trade winds (trade winds blow toward the equator) N N - (fig 14.11, p466) Jet Streams A jet stream is a ribbon of fast moving air caused by the contrast between warm and cool air. Jet streams move air at a minimum of 100 km/h, average around 300 and can be as fast as km/h in the winter. These "streams" are not always a clearly defined strip. They may be several wide, but are only a few kilometres deep. Because jet streams are caused by differences in temperatures, the jets form at the boundaries between the climatic zones. There are 4 jet streams: the jet 60 N ; the jet 30 N; and the same in the southern hemisphere. All jet streams move from west to east, but meander north and south, pulled by the rotation of high and low pressure systems.

3 3 Jet Streams Influence Weather Jet streams have a major impact weather patterns. They act as a to warm and cool systems. When a jet stream drops down to the south, it allows systems with air to move in from the north. Conversely, when a jet moves north, it allows air systems to come up from the south. In Saskatoon (52 N), this difference is especially prominent in the winter and spring. The jet stream's average position will move north or south depending on the time of year and the angle of the sun's light. (fig 14.15, p467) Chinook Chinook is a First Nations word that means " ". When the mountains cause moist pacific air to rise and condense, much rain or snow fall in the mountains. Water changes from vapour to liquid to snow, which releases thermal energy, warming the air. When this blows across the prairies in the winter, it can change conditions dramatically in a short time. On January 6, 1966, a chinook raised the temperature in parts of Alberta by 21 C in 4 minutes! Cloud Types When water evaporates into the atmosphere, it rises, cools, and condenses. This forms clouds. There are 3 main types of clouds: (L. heap) - Cotton like clouds, formed when air rises quickly over a small area. (L. covering or blanket) - Grey, flat clouds that usually cover the whole sky, formed when air rises over a large area. (L. curl) White wispy clouds formed very high, made of ice crystals. Nimbus (L. rain cloud) - a descriptor of a cloud that produces rain. Alto - a descriptor that means middle Cloud types can be made from a combination of these. (fig 15.5, p490) Low Clouds ( m) Stratus, Nimbostratus, Stratocumulus Middle Clouds ( m) Altostratus, Altocumulus High Clouds (6000+ m) Cirrus, cirrostratus, cirrocumulus All Levels Cumulus, Cumulonimbus Weather Systems A weather system is a set of temperature, wind, pressure, and moisture conditions for a region that move as a unit for a period of days. Two types of weather systems are and pressure. Low pressure systems typically result in and stormy weather. They are caused by air, either by solar heating, or by a frontal low. When air rises, it condenses and forms clouds. Where warm and cool air masses meet, a front forms. Fast flowing air from the jet stream pulls air out of both air masses and causes the air to rise. (frontal low, fig 15.18, p501) Due to the Coriolis effect, the rising air rotates counterclockwise in the northern hemisphere. The leading edge of the warm air is called a, and the cool air's - a. The

4 4 cold front moves about as fast as the warm front, and pushes it up as it goes. This usually produces clouds, but if the cold front is moving rapidly, cumulonimbus clouds and intense thunderstorms follow. (fig 15.12, p497) At the same time, the warm front rises gently over the cool air. This usually produces clouds, followed by altostratus and cirrus as it climbs higher. (fig 15.13, p497) Once the cold front catches up with the warm front, the low is cut off from the warm air and the lifting effects of the jet stream. This is known as an front, and the low starts to weaken. Both warm and cold fronts can cause, Cold fronts are typically heavier storms, that are over quickly, leaving the temperature cooler. Warm fronts may last for days, are less intense, and may leave the temperature warmer. High pressure systems usually result in skies. They are caused by air that cools, becomes more dense, and falls. Highs rotate in the northern hemisphere, and may be hundreds of kilometres across. Because they are so large, they could mean similar weather conditions for several days. Ocean Currents set the oceans in motion. For example, a westerly wind would cause water below it to also flow toward the east. Figure on p469 has the major ocean currents and their relative temperatures. Notice the similarity to the pattern of prevailing wind. When wind moves water in one direction, water rushes in to replace it. This causes circular water patters called. In general, gyres are in the northern hemisphere, and counter clockwise in the southern hemisphere. The water on the east side of a gyre tends to be cooler, which also makes the air above it cooler (warm water also causes warmer air). Cooler air holds less moisture, and if that air moves over land, will not produce much precipitation. Conversely, if warm moist air moves over land, it creates a humid, rainy environment. El Nino and La Nina El Nino is the name given to an area of than normal water off the coast of Ecuador and Peru. This area is 1.5 times the size of Canada and is the world's second largest driver of weather (next to seasons). El Ninos usually occur every 2 to 7 years and last for 12 to 18 months. The name El Nino means "the child (boy)" and is named after the Christ child because they typically begin in December. An El Nino is a reversal of the normal weather patterns that usually see warm water near Australia and cooler water near Peru. This is because trade winds blow the warm water near the equator to the west. The sea level is m near Australia than near Peru. This current pulls colder water from below on the eastern side to replace the warmer water (upwelling). For an unknown reason, the trade winds reverse and blow the "pile" of warm water across the ocean. (Fig 14.21, p476) In Saskatoon, an El Nino causes a, winter. The El Nino of was the strongest on record (5 C above normal), and caused droughts, crop failures and even a December fire on the prairies. El Nino was also blamed for a massive ice storm in eastern

5 5 Canada that January. The previous strongest El Nino caused Australia's worst drought in 200 years, 18 billion dollars in damage, and 2000 deaths. La Nina, "the girl," is a of the water near Ecuador and Peru by as much as 4 C below normal. La Ninas occur less frequently than El Ninos, at about every 4 to 5 years. The effects of La Nina are less pronounced than, and usually opposite to El Nino. In Saskatoon, La Nina causes a winter with snow. It also tends to promote Atlantic hurricanes, whereas El Nino suppresses them. Severe Weather Lightning We have already learned how thunderstorms form. Lightning occurs because charges have built up in the clouds, perhaps from friction among the moving water and ice pellets in a storm. Electrons flow from areas of negative charge to positive, which is usually cloud to ground, but may be the reverse. A typical bolt is km long, but it can easily travel km before turning downward. Under ideal conditions, km from the strike is the farthest you will hear thunder, but it may be as low as 3 km. If you can hear thunder, you can be struck. You can use the 3 seconds/km rule for calculating distance to a strike. Lightning can travel with lethal charge through the ground for about m and in water for about m. Most lightning is about wide and is around C, 5 times hotter than the surface of the sun. Around the world, there are nearly thunderstorms per day, and even though 90% of lightning is within the clouds, lightning hits the ground about times per second. Lightning only kills about 10% of its victims, but one third of the survivors suffer long term medical problems. (NLSI) Tornadoes Scientists aren't sure how tornadoes form, but most theories involve a cell that begins to rotate. An area of low pressure at the centre draws the cyclone downward and it narrows. In doing so, its speed increases the same way a figure skater speeds up by pulling the arms in. Tornadoes are classified from to to on the Enhanced Fujita scale based on their wind speed and damage. (table 15.1, p507) Tornadoes occur on every continent except Antarctica. On average, Saskatchewan sees 23 tornadoes per year. Hurricanes Although hurricanes don't have the wind speeds of some tornadoes, but they can be 500 km across, and last for days. As a result, they can cause much more extensive destruction. The name "hurricane" may come from the Mayan god of wind,. In the western Pacific, they are called typhoons and in the Indian Ocean, tropical cyclones. However, they are essentially the same. Just like normal low pressure systems, hurricanes spin counterclockwise in the northern hemisphere, and clockwise in the southern. Hurricanes do not form over the equator because the effect is absent there. Intense low pressure at the centre of the hurricane creates a "pile" of water, that, when it hits land, creates a storm surge. A storm surge can be as high as 6 m higher than sea level, and cause many of the fatalities. Hurricane wind strength ranges from km/h (category 1) to 250 km/h + (category 5). This compares with a minimum 37 km/h for a tropical depression, and 65 km/h for a tropical storm. (fig 15.26, p509)