# Ch19 FI

 Lesson 1 Air Pressure The pressure exerted by the weight of air above.Avg air pressure at sea level: 1kg/cm2. Air pressure is exerted in all directions --down, up & sideways.Air pressure pushing down on an object balances the air pressure pushing up on the object. Air pressure Air pressure is exerted in all directions-down,up, and sideways. The air pressure pushing down on an object balances the air pressure pushing up on the object. barometer A device used for measuring air pressure, design by Torricelli, student of Galileo.Standard sea-level pressure = 1013.2 millibars. mercury levels When air pressure increases, the mercury in the barometer's tube rises. When air pressure decreases, so does the height of the mercury column wind Wind is the result of horizontal differences in air pressure. Air flows from areas of higher pressure to areas of lower pressure. What causes the difference in atmospheric pressure? The unequal heating of Earth's surface generates pressure differences. Solar radiation is the ultimate source of energy for most wind What factors combine to control wind? presuure differences, Coriolis effect & friction Wind created by differences in pressure:the greater the difference, the greater the wind speed. Isobars lines on a map that connect places of equal air pressure. Pressure Gradient The spacing of isobars indicates the amount of pressure change occurring over a given distance. These pressure changes are expressed as the pressure gradient Isobar spacing Closely spaced isobars indicate a steep pressure gradient and high winds. Widely spaced isobars indicate a weak pressure gradient and low winds.Direction of force is always from higher pressure to lower pressure & at right angles to the isobar.Friction affects wind speed & direction.Coriolis effect affects wind DIRECTION only Coriolis Affect Describes how the Earth's rotation effects moving objects. Strongest at the poles. Directed @ 90 degree angles to that of airflow Coriolis effect describes how rotation affects moving objects or fluids, including the wind, are deflected to the right of their path of motion in the Northern Hemisphere. In the Southern Hemisphere, they are deflected to the left.Earth rotates at 15o/hr; therefore the Coriolis effect deflects at 15o/hr. Shift in wind direction is attributed to the Coriolis effect This deflection:1) is always directed at right angles to the dirction of airflow2) affects only wind direction and not wind speed3) is affected by wind speed---th stronger th wind, th greater the deflection4) is strongest at the poles and weakens toward the equator, bcoming nonexistent at the equator How many degrees does Earth rotate in one day? 15o x 24 = 360o Friction effect of friction on wind is important only w/in a few kilometers of Earth's surface.friction slow air movement, which changs wind direction. Compare friction over smooth ocean surface vs. friction over rugged terrain? Friction over smooth ocean surface is low & angle of airflow is small Friction over rugged terrain is high & winds move more slowly across the isobars at greater angles. Jet Streams Fast-moving rivers of air near the tropopause that travel between 120 and 240 kilometers per hour in a west-to-east direction. Why don't objects such as a table collapse under the weight of the air above? Because the object emits the same amount of pressure outward as the air above it air pressure pushing down on an object balances the air pressure phushing up on the object. Suppose the height of a column in a mercury barometer is decreasing. What is happening? The air pressure is decreasing. If height of mercury column rises = pressure is increasing. What happens to mercury column of a barometer when air pressure changes? When column of mercury decreases = air pressure decreasingWhen column of mercury increases = air pressure increasing What is the ultimate energy source for wind? the difference in the atmospheric pressure caused by the uneven heating of the earth by the Sun. Air pressure travels from high to low, creating wind. How does the Coriolis effect influence free-moving objects? In the Northern Hemisphere it deflects things to the right. In the Southern Hemisphere it deflects things to the left. The rate of deflection is 15o/hr Why do jet streams flow parallel to isobars? in the tropopause or upper-level, jet stream flow can be almost parallel to the surface flow because of the Coriolis effect & pressure gradient forces. Cyclones Are centers of low pressure. Anticyclones Are centers of high pressure. 2 significant factors that affect wind pressure gradient & Coriolis effect:wind blows from higher to lower & are deflected to right or left by Earth's rotation Explain the pressure changes in outer isobars toward the center of cyclones & anticyclones In cyclones, the pressure decreases from the outer isobars toward the center. In anticyclones, just the opposite is the case-the values of the isobars increase from the outside toward the center Explain the pressure gradient & Coriolis effect on the pressure centers in the Northern Hemisphere: When the pressure gradient and the Coriolis effect are applied to pressure centers in the Northern Hemisphere, winds blow counterclockwise aroud a low. Around a high, they blow clockwise. How does friction control net flow of air around a cyclone and an anticyclone? In either hemisphere, friction causes a net flow of air inward around a cyclone and a net flow of air outward an anticyclone. With what type of weather is rising air associated? rising air = cloud formation & precipitation or unstable condition & stormy weathersinking air = clear skies, good weather In general, what type of weather can you expect if a low-pressure system is moving into your area? low presssure:-cloudy conditions & precipitation or stormy weather high presssure:- clear skies & fair weather airflow patterns: surface & aloft (upper air) air spreads out (diverges) above the surce of cyclonesair comes togehter (converges) above surface of anticyclones Describe how winds blow around pressure centers in the Northern and Southern Hemispheres. Northern Hemisphere:Low (cyclone) = counterclockwiseHigh (anticyclone) = clockwise opposite in Southern Hemisphere:Low (cyclone) = clockwiseHigh (anticyclone) = counterclockwise Describe how winds blow around pressure centers in the Northern Hemisphere. Northern Hemisphere:Low (cyclone) = counterclockwiseHigh (anticyclone) = clockwise Compare the air pressure for a cyclone with an anticyclone Cyclone = Low pressure systemAnticyclone = High pressure sytem What is the only truly continuous pressure belt? Why is it continuous? the Trade winds, 2 belts of winds that blows almost constantly from easterly directions & are located b/t the subtropical highs & the equator. How does the atmosphere balance the unequal heating of Earth's surface? The atmosphere balances these differences by acting as a giant heat-transfer system.This system moves warm air toward high latitudes and cool air toward the equator. Trade Winds Two belts of winds that blow almost constantly from easterly directions.Trade winds are located b/t the subtropical highs & the equator. What is the ploar front? stormy frontal zone separating cold air masses of polar origin from warm air masses of tropical origin Westerlies They make up the dominant west-to-east motion of the atmosphere that characterizes the regions on the poleward side of the subtropical highs. They usually move the weather west-to-east Polar Easterlies Winds that blow from the polar high toward the subpolar low Polar Front The stormy belt in the middle latitudes. What is the polar front? The Polar front is where the westerlies and polar easterlies meat. What's the influence of continents on global pattern of pressure zones in the atmosphere? Landmasses break up the ocean surface & large seasonal tempreature differences disrupt the global pattern of pressure zones in the atmosphere. In the winter in Northern Hemisphere, large land masses become cold in winter when a seasonal high-pressuresystem develops, causing surface airflow off the land.In the summer, landmasses are heated & develop low-pressure cells, which permits air to flow onto the land. Monsoons Seasonal changes in wind direction. Section 19.3 Regional Wind Systems local winds Small-scale winds produced by a locally generated pressure gradient. What causes local winds? The local winds are caused either by topographic effects or by variations in surface composition-land and water-in the immediate area Examples of local winds Land & Sea breezesValley & mountain breezes Land & Sea breezes During the day, land heats up faster, causing the air to rise & thus lower pressure on surface, this cause the higher pressure & cool air of the water to push onto land, giving a cool breeze. At night, the land cools faster, causing higher pressure near surface, causing cool wind to blow out onto lower pressure water. Valley & Mountain Breezes valley breeze (dominant in warm season):During daylight hours, air along the slopes of mountains heated more intensely than air at same elevation over valley floor, causing the warm, less dense air to glide up the slopes., generating a valley breeze. mountain breeze (dominant in cold season):At night, rapid cooling of air along the mountain slopes produces a layer of cooler mor dense air next to the ground, causing it to move downslope What type of local wind cand form in the Grand Canyon at night? Mountain Breeze What's the prevailfing wind in the US? the westerlies consistenly move weather from west to east across the continent. Prevailing Wind When the wind consistently blow more often from one direction than from any other Anemometer Common device used to measure wind speed What is El Nino & La Nina El Nino = warm La Nina = cold El Niño and La Niña result from interaction between the surface of the ocean and the atmosphere in the tropical Pacific. Changes in the ocean impact the atmosphere and climate patterns around the globe. In turn, changes in the atmosphere impact the ocean temperatures and currents. The system oscillates between warm (El Niño) to neutral (or cold La Niña) conditions with an on average every 3-4 years. El Nino ("the child" =after the Christ child) At irregular intervals of three to seven years, these warm countercurrents become unusually strong and replace normally cold offshore waters with warm equatorial waters La Nina when surface temperatures in the eastern Pacific are colder that average, a La Nina event is triggered that has a distinctive set of weather patterns El Niño and La Niña are extreme phases of a naturally occurring climate cycle referred to as El Niño/Southern Oscillation. Both terms refer to large-scale changes in sea-surface temperature across the eastern tropical Pacific Describe the general movement of weather in the U.S. West-to-east What happens wen unusually strong,warm ocean currents flow along the coasts of Ecuador and Peru? El Nino happens. How is a La Nina event triggered? when surface temperatures in the eastern Pacific are colder than average. Toward which direction does a SE wind blow? To the NW What is and El Nino and what effect does it have on weather? unusually strong countercurrents accumulate large quantities of warm water tht block the upwelling of colder, nutrient-filled water, causing anchovies to starve & devasting the fishing industry.causes abnormal weather patterns that drastically affect the economise of Ecuador & Peru. How is a La Nina event recognized? when surface temperatures in the eastern Pacific are colder than average. What two factors mainly influence global precipitation? El Nino & El Nina Summarize the general wind patterns in the Northern Hemisphere and in the Southern Hemisphere? Global Circulations explain how air and storm systems travel over the Earth's surface. The global circulation would be simple (and the weather boring) if the Earth did not rotate, the rotation was not tilted relative to the sun, and had no water. In a situation such as this, the sun heats the entire surface, but where the sun is more directly overhead it heats the ground and atmosphere more. The result would be the equator becomes very hot with the hot air rising into the upper atmosphere. That air would then move toward the poles where it would become very cold and sink, then return to the equator (above right). One large area of high pressure would be at each of the poles with a large belt of low pressure around the equator. However, since the earth rotates, the axis is tilted, and there is more land mass in the northern hemisphere than in the southern hemisphere, the actual global pattern is much more complicated. Instead of one large circulation between the poles and the equator, there are three circulations...Hadley cell - Low latitude air movement toward the equator that with heating, rises vertically, with poleward movement in the upper atmosphere. This forms a convection cell that dominates tropical and sub-tropical climates. Ferrel cell - A mid-latitude mean atmospheric circulation cell for weather named by Ferrel in the 19th century. In this cell the air flows poleward and eastward near the surface and equatorward and westward at higher levels. Polar cell - Air rises, diverges, and travels toward the poles. Once over the poles, the air sinks, forming the polar highs. At the surface air diverges outward from the polar highs. Surface winds in the polar cell are easterly (polar easterlies). Between each of these circulation cells are bands of high and low pressure at the surface. The high pressure band is located about 30° N/S latitude and at each pole. Low pressure bands are found at the equator and 50°-60° N/S. Usually, fair and dry/hot weather is associated with high pressure, with rainy and stormy weather associated with low pressure. You can see the results of these circulations on a globe. Look at the number of deserts located along the 30°N/S latitude around the world. Now, look at the region between 50°-60° N/S latitude. These areas, especially the west coast of continents, tend to have more precipitation due to more storms moving around the earth at these latitudes.http://www.srh.noaa.gov/srh/jetstream/global/circ.htm Authorsuperman237 ID78352 Card SetCh19 FI DescriptionNote Cards Updated2011-04-11T06:35:29Z Show Answers