EARTH SCIENCE 5.9 (WIND) WEATHER

Transcription

1 EARTH SCIENCE 5.9 (WIND) WEATHER Video Notes Key Points: 1. According to the video, what two factors cause wind: a. b. 2. Fill in the blanks from this quote from the video: Energy from the Sun heats the, and the heat warms the air over the. 3. According to the video, when the air molecules go faster, they don t weigh as much. What happens to the cold air after this? 4. The video shows smoke representing cold air. Where is the air sinking on the model? (Hint: He says the air is sinking over the cold what?) 5. He then says that the air is rising over the warm parts? If you were looking at a model of the Earth, where would the warm parts be? 6. Why does wind come from all different directions? Earth Model: 9 th GRADE 5

2 EARTH SCIENCE 5.9 (WIND) WEATHER Video II Notes: 1. How does wind happen: 2. Fill in this quote from the clip: Air near the is heated by energy of the Sun, so it becomes less and. 3. Fill in this quote from the clip: Near the, there s not as much heating by the Sun, and that cold, dense air down toward the Earth. 4. The turning of wind belts because of Earth s rotation is known as the. (Note: We will learn more about this later!) What is Wind? Wind is simply air in motion. It is produced by uneven heating of the Earth s surface by energy from the Sun. Since the Earth s surface is made of very different types of land and water, and the tilt of the Earth causes insolation to heat locations on the Earth at different rates, the Earth heats at different rates. When insolation strikes different surfaces, some of that energy is converted into heat, which also heats the surrounding air. The energy of wind comes from the Sun. When the Sun shines, more of the radiant energy (insolation) reaches the tropics/equatorial region than the poles. Even despite this, some types of land absorb more sunlight than others (for example, the sands of the desert reflect a lot of sunlight, which reduces the amount of heat absorbed). When this insolation is absorbed, the land turns this into heat (think of a blacktop on a hot summer day, or how hot a sandy beach is in August). As this air warms, it expands. The molecules get farther apart. The warm air is then less dense than the air around it and rises in the atmosphere. Cooler, denser air nearby flows in to take its place. This movement of air is what we call wind. It s caused by the uneven heating of Earth s surface. 9 th GRADE 6

3 EARTH SCIENCE 5.9 (WIND) WEATHER How is wind formed? At Earth s surface, winds blow in response to differences in air pressure. Winds always move from places of higher pressure to places of lower pressure (i.e. along a pressure gradient). When you exhale, you do so by squeezing the air in your lungs, increasing the pressure. Air escapes from your body to equalize the pressure inside and outside your lungs. You learned earlier that atmospheric pressure is caused by the weight of the atmosphere. Differences in the density of air cause changes in the weight of the air. Primarily, temperature and humidity determine the density of air. (As temperature and humidity increase, air becomes less dense.) When air density increases, so does air pressure at Earth s surface, forcing the air to move to places with a lower surface pressure. This often creates a localized convection cell, where regions of high pressure and low pressure circulate as density changes as a result of temperature. 9 th GRADE 7

4 Flight times from JFK (in NYC) to SFO (San Francisco): Flight times from SFO to JFK: 2

5 Video - Define the following two terms: 1. According to the video, warm air weighs less than cool air. This creates a pressure area. Similarly, cool air is, and creates an area of pressure 2. A narrow band of fast-moving air about eight (8) miles above the Earth is referred to as the. a. The jet stream influences weather across the Northern hemisphere b. When the jet stream moves over the ocean, it often creates a region of, or a surge of warm air rushing up from the ocean 3. According to the video, what is wind:. 4. What prevents winds from blowing directly North or South toward the Equator: 5. Instead, the winds that blow toward the Equator curve 6. Winds the blow away from the Equator move toward the a. This phenomenon is called the 7. A mass of air that moves together in a circular motion is a a. Cold air sinks at the and then flows North or South, where it and again to complete a polar cell 3

6 Prevailing Winds: In New York State, winds blow from the west and southwest more often than they come from any other direction. Remember, winds are labeled according to the direction you face when you look into the wind. Prevailing winds refer to the most common wind direction and speed at a particular location and time of year. The picture below shows how winds might blow if Earth were not spinning. Cold air would sink at the poles and travel along the surface toward the Equator. Strong sunlight heating the air near the equator would cause the air to rise and move back toward the poles. Two large convection cells, as shown in the vertical profile, would dominate planetary winds. Why would the air sink at the poles and rise at the Equator: Earth s rotation modifies this motion through the Coriolis effect, as shown in the second image below. Winds curving to the right in the Northern Hemisphere and to the left in the Southern Hemisphere break the two convection cells shown in the first image into six convection cells. Within each cell, winds curving to the right in the Northern Hemisphere and to the left in the Southern Hemisphere change the North and South winds into winds east and west winds. Regional weather systems (highs and lows) complicate the pattern even more. Winds can come from any direction depending on changes in the pressure gradient. 4

7 The Jet Stream: Jet streams were discovered during the Second World War when the pilots of high-altitude aircraft found themselves traveling much slower than their air speed indicated. Today, aircraft will sometimes change their flight paths to take advantage of fast tail winds, or to avoid fighting head winds. Wandering currents of air far above Earth s surface are known as jet streams. With wind speeds that can be greater than 160 km/h (100 mph), jet streams circle the globe, usually in the middle latitudes. Jet streams seldom follow surface winds and usually occur where cold polar air meets warmer air in the mid-latitudes. They circle the globe from west to east, usually in the upper part of the troposphere. This west to east motion is also what drives most storms that pass through the United States! 5

8 The path of the jet stream is changeable as it meanders around the globe. In fact, two jet streams sometimes develop in the Northern Hemisphere. They tend to occur at the northern and southern limits of the zone of prevailing westerly winds. The image on the previous page, taken from the Earth Science Reference Tables, is a generalization of the pattern of winds on our planet. This diagram shows the large convection cells responsible for prevailing surface winds at various latitudes. Notice how the jet streams generally occur in the regions between the circular convection cells. Q: A storm starts to form in the Arizona. According to the jet stream, which direction will it travel over the next few days: Practice: 1.) 2.) 3.) 4.) 6

9 5.) 6.) 7.) 8.) 9.) 7

10 10.) What is meant by prevailing winds? Answer: 10.) 11.) 8

11 12.) 13.) 14.) 9

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