3 Notes Chapter 16.11. Air pressure is the force of air molecules pushing on an area. The greater the force the higher the air pressure because air molecules move in all directions. AIR PRESSURE PUSHES IN ALL DIRECTIONS.
4 2. Air pressure decreases as altitude increases 2. Air pressure decreases as altitude increases. Air pressure increases as altitude decreases.
5 3. Air pressure and density are related 3. Air pressure and density are related. The denser the air is, the greater the pressure. Areas of low pressure are less dense.4.Air pressure is different in different areas of the atmosphere. Because of the differences in pressure air starts to move from areas of high pressure to areas of low pressure.5. The instrument used to measure air pressure is the barometer.
6 Chap 16.2 notesWeather is the condition of the Earth’s atmosphere at a certain time. Wind is an important part of weather.Wind is air that moves horizontally or parallel to the ground.Uneven heating of the Earth’s surface causes pressure differences. This uneven heating sets the air(wind) in motion.
7 4. Cooler air sinks causing high pressure 4. Cooler air sinks causing high pressure. Air (wind) moves across the surface of the earth getting warmer. This creates a low pressure area. Then the warmer air rises to cool again. The changing pressure (from high to low and back again) is what creates the wind.Drawing of winds5. Global winds are caused by uneven heating between the North Pole and the Equator and the South Pole and the Equator.Equator- warm air low pressurePoles- cool air high pressure
8 6. The influence of Earth’s rotation is called the Coriolis effect 6. The influence of Earth’s rotation is called the Coriolis effect. Global winds curve as Earth turns beneath them. N. Hemisphere winds curve to the right. S. Hemisphere to the left.7. Coriolis effect keeps winds from traveling from the poles directly to the equator. They travel in 3 global wind belts.8. Earth’s rotation and the uneven heating of its surface cause a pattern of wind belts separated by calm regions. Doldrums, low pressure areas along the equator, the horse latitudes are high pressure areas 30 degrees north and south of the equator.
9 9. Wind belts are the trade winds, the westerlies, and the easterlies 9. Wind belts are the trade winds, the westerlies, and the easterlies. Why do you think the trade winds were so named? Which belt do we live in?10. Jet stream usually flow in the upper troposphere from west to east for thousands of kilometers. Air often moves in jet streams at speeds greater that 200 kilometers per hour. Jet streams occur because of the uneven heating of the earth’s surface.11. Sea breezes and land breezes occur near shoreline. During the day, the land heats up faster than the water. This causes the winds to blow from the water to the land because of the cooler air over the oceans and the warmer air over the land. At night the reverse happens. The land cools much more rapidly than the water so the winds blow from the cooler land to the warmer water.
11 16.3-Humidity is the amount of water vapor in the air. Humidity varies from place to place and time to time. High humidity makes it hard for water vapor to evaporate from your skin, so you feel hotter.As water molecules evaporate into the air some start to condense. Air gains water vapor because more water evaporates than condenses. But the air will reach saturation when the rate of evaporation and condensation are equal.
12 3. If humidity is low, you feel cooler 3. If humidity is low, you feel cooler. If the humidity is high, you feel hotter.4. Water vapor evaporates and rises in the air. As it rises, it cools. This causes condensation which makes clouds. Water vapor condenses on small particulates such as dust, smoke, and salt from the ocean.5. When water droplets that have formed around particulates get heavy enough, they fall as precipitation.
13 6. Clouds form under different conditions 6. Clouds form under different conditions. Puffy clouds form when air rises sharply or moves straight up and down. Flat smooth clouds form in air that rises gradually. At high altitudes clouds are made of ice crystals. Clouds that are lower to the ground are made of water droplets or a mixture of droplets and crystals.
14 ChapterAll precipitation comes from clouds. Precipitation can form when cloud droplets combine. Droplets move up and down in clouds and as they bump into each other they combine. As they continue to move they bump into more droplets until they get big and heavy enough to fall.Another way precipitation forms is by ice crystals growing. When the temperature in the cloud is below freezing the water vapor changes into ice crystals. Crystals grow like the droplets do and when they get larger and heavy enough they fall from the clouds.
15 Chapter cont3. Types of precipitation (turn to page 564 and define each of these types of precipitation)1. Rain or drizzle-form from water droplets or ice crystals that melt as they fall2. Freezing rain-is rain that freezes when it hits the ground or other surfaces3. Sleet-is rain that freezes into ice pellets while falling through cold air
16 4.Snow-forms from ice crystals that merge into clouds. 5. Hail-forms when ice pellets move up and down in clouds growing larger as they gain layers of ice.