geography exam 2

intertropical convergence zone (ITCZ)

warmer, less dense air along the equator rises, creating the low pressure region of this

Antarctic high

A consistent high-pressure region centered over Antarctica; source region for an intense polar air mass that is dry and associated with the lowest temperatures on Earth

mercury barometer

A device that measures air pressure using a column of mercury in a tube; one end of the tube is sealed, and the other end is inserted in an open vessel of mercury.

aneroid barometer

A device that measures air pressure using a partially evacuated, sealed cell.

anemometer

A device that measures wind velocity

anticyclone

A dynamically or thermally caused area of high atmospheric pressure with descending and diverging airflows that rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

cyclone

A dynamically or thermally caused area of low atmospheric pressure with ascending and converging airflows that rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

polar front

A significant zone of contrast between cold and warm air masses; roughly situated between 50° and 60° N and S latitudes.

Hawaiian high

A subtropical high-pressure cell, centered over the Pacific Ocean about 1600 km northeast of Hawai'i.

Pacific high

A subtropical high-pressure cell, centered over the Pacific Ocean about 1600 km northeast of Hawai'i.

wind vane

A weather instrument used to determine wind direction; winds are named for the direction from which they originate.

geostrophic winds

A wind moving between areas of different pressure along a path that is parallel to the isobars. It is a product of the pressure gradient force and the Coriolis force.

monsoons

An annual cycle of dryness and wetness, with seasonally shifting winds produced by changing atmospheric pressure systems; affects India, Southeast Asia, Indonesia, northern Australia, and portions of Africa. From the Arabic word mausim, meaning "season."

ridges

An elongated region of high air pressure, usually oriented north-south.

troughs

An elongated region of low air pressure, usually oriented north-south.

isobar

An isoline connecting all points of equal atmospheric pressure.

Rossby waves

An undulating horizontal motion in the upper-air westerly circulation at middle and high latitudes.

Higher wind speeds at troughs: winds near the area of maximum wind speeds along the troughs accelerate and diverge, causing low pressure air to converge and ascend from the surface.

Are higher wind speeds associated with ridges or troughs? Explain why this occurs.

Air pressure is created by the motion, size, and number of molecules. Air molecules in the atmosphere are pulled toward the center of Earth by gravity. The molecules bounce off each other, creating air pressure through their motion and number. Air molecules exert more force when they are closer together, as at Earth's surface, or when the temperature is higher and they are moving more quickly

How does air exert pressure?

- wind and pressure contribute to earth's general atmospheric circulation, which drives weather systems and spreads natural and anthropogenic pollution across the globe - natural oscillations in global circulation, such as ENSO, affect global weather - ocean currents carry human debris and non-native species into remote areas and spread oil spills across the globe

How does atmospheric and oceanic circulation impact humans?

In general, rougher surfaces produce more friction. Because surface friction decreases wind speed, it reduces the effect of the Coriolis force and causes winds to move across isobars at an angle.

How does friction affect surface winds?

- Temperature of Tropics: The tropics are warm all year, averaging 25 to 28 degrees Celsius (77 to 82 degrees Fahrenheit). - Precipitation of Tropics: There are basically three seasons - the dry season (December - April), the wet season (May - August), and the possibly very wet season (September through November) - Temperature of ITCZ and trade winds: warm all year, 12-hour days - Precipitation of ITCZ and trade winds: The air is also dry because of the moisture that was lost as precipitation as the air initially rose in the ITCZ. This will bring dry weather. In the ITCZ, warm, moist air rises and cools, releasing latent heat and producing condensation and rainfall. This will bring wet weather.

Relate the general temperature and precipitation characteristics of the tropics to the ITCZ and the trade winds.

El Niño

Sea-surface temperatures increase, sometimes more than 8 C° (14 F°) above normal in the central and eastern Pacific, replacing the normally cold, nutrient-rich water along Peru's coastline. Pressure patterns and surface ocean temperatures shift from their usual locations across the Pacific, forming the Southern Oscillation.

- named El Niño ("the boy child") because these episodes seem to occur around Christmas, they can occur as early as spring and summer and persist through the year. The expected interval for ENSO recurrence is 3 to 5 years. The frequency and intensity of ENSO events increased through the 20th century. - During an El Niño, air pressures and trade winds shift (Fig. 3.23b). Air pressure is higher than usual over the western Pacific and lower than usual over the eastern Pacific. The shift in air pressure causes the northeast trade winds to weaken and even reverse. The change in wind and ocean current direction causes cooler sea-surface temperatures in the western Pacific. At the same time, sea-surface temperatures increase up to 8°C (14°F) above normal in the central and eastern Pacific as warm water replaces the normally cold, nutrient-rich water along Peru's coastline. - The shift in air pressure patterns and ocean temperatures create the El Niño-Southern Oscillation, or ENSO. Higher air pressure over the western Pacific causes drier conditions, while the lower air pressure over the eastern Pacific is associated with rising air and wetter conditions. The shift in air pressure also causes equatorial ocean currents to weaken or reverse. - Normally, the current flowing eastward away from the west coast of South America creates an upwelling of cold water. During an ENSO, the wind and warm surface waters flow toward the South American coast slowing the upwelling currents of nutrient-rich water. This loss of nutrients affects the entire marine food chain, from plankton to birds and seals that feed on fish. LA NINA: - When surface waters in the central and eastern Pacific cool below normal, the condition is dubbed La Niña, Spanish for "the girl" (Fig. 3.23c). This condition is weaker and less consistent than El Niño. The strength or weakness of an El Niño does not correlate with the strength or weakness of La Niña, or vice versa. Following the record 1997-1998 ENSO event, the subsequent La Niña was not as strong as predicted. - In contrast, the 2010-2011 La Niña was one of the strongest on record. In Australia, this event corresponded with the wettest December in history. Heavy rainfall led to the country's worst flooding in 50 years in Queensland and across eastern Australia. Weeks of precipitation flooded an area the size of France and Germany combined and caused the evacuation of thousands of people.

Summarize the main effects and timescales of the El Niño-Southern Oscillation. Explain what patterns are affected by ENSO. Describe the changes in sea-surface temperatures and atmospheric pressure that occur during El Niño and La Niña, the warm and cool phases of the ENSO.

subpolar low

pressure cells - A region of low pressure centered approximately at 60° latitude in the North Atlantic near Iceland and in the North Pacific near the Aleutians as well as in the Southern Hemisphere. Airflow is cyclonic; it weakens in summer and strengthens in winter.

subtropical high

pressure cells - One of several dynamic high-pressure areas covering roughly the region from 20° to 35° N and S latitudes; responsible for the hot, dry areas of Earth's arid and semiarid deserts

polar high

pressure cells - Weak, anticyclonic, thermally produced pressure systems positioned roughly over each pole; that over the South Pole is the region of the lowest temperatures on Earth

*figures 3.3**

Construct a simple diagram of Earth's general circulation, including the four principal pressure belts and the three principal wind systems.

thermohaline circulation

Deep-ocean currents produced by differences in temperature and salinity with depth; earth's deep currents

- Air pressure is the weight of air molecules pressing down on the Earth. it fluctuates due to a variety of reasons, and these fluctuations can create phenomena like wind

Define the concept of air pressure.

Differences in air pressure between one location and another produce this, the horizontal motion of air; flows from areas of higher air pressure toward areas of lower air pressure

Define wind.

Air pressure is measured using a barometer. In 1643, Evangelista Torricelli invented a device for measuring air pressure—the *mercury barometer* (Fig. 3.2). Torricelli sealed a 1 m tall glass tube at one end, filled it with mercury (Hg), and inverted it into a dish of mercury. He determined that the average height of the column of mercury in the tube was 760 mm (29.92 in.) and that it varied day to day as the weather changed. A more compact design is the *aneroid barometer.* The aneroid barometer principle is simple: A small chamber, partially emptied of air, is sealed and connected to a mechanism attached to a needle on a dial. As air pressure increases, it compresses the chamber; as air pressure decreases, the chamber expands—changes in air pressure move the needle. An aircraft altimeter is a type of aneroid barometer.

Describe instruments used to measure air pressure. Compare and contrast a mercury barometer and an aneroid barometer.

ngl girl idk look thru some diagrams prob 3.1, 3.2

Describe or draw a diagram showing how the principal winds would blow if Earth rotated in the opposite direction. Include the warm and cold surface ocean currents.

Ocean currents are driven by the winds flowing out of the subtropical high-pressure cells in both hemispheres (Fig. 3.20). The large circular currents in the oceans are called gyres. Because ocean currents flow over long distances, the Coriolis force deflects them. The circular flow of ocean currents transports warm water from the equator to the poles, where the water cools and moves back to the equator. The trade winds drive the ocean surface waters westward along the equator. When these currents reach the eastern shores of the continents, water actually piles up to an average height of 15 cm (6 in.). This phenomenon, called the western intensification, forms poleward-moving currents. The piled-up water moves poleward in tight channels along the eastern shorelines of the continents. In *video from 3.6*

Describe the basic pattern of Earth's major surface ocean currents.

Heating differences between land and water produce the land and sea breezes that occur on most coastlines mountain and valley breezes result from mountain air cooling rapidly at night and valley air heating rapidly during the day Strong, dry winds sometimes flow across the desert towards Southern California coastal areas. These Santa Ana winds occur when high pressure builds over the Great Basin of the western United States in the fall, with low-pressure offshore Usually stronger than local winds and of larger, regional scale, katabatic winds occur when air at the surface cools, becomes denser, and flows downslope from an elevated plateau or highland. Gravity winds are not specifically related to the pressure gradient. Regional winds are part of Earth's secondary atmospheric circulation. The monsoons are seasonally shifting wind systems caused by the annual cycle of migrating pressure belts.

Describe the conditions that produce several types of local winds.

Differences in density caused by differences in temperatures and salinity produce deep currents called thermohaline circulation (thermo- refers to temperature and -haline refers to salinity, or the amount of salts dissolved in water). Although these currents flow more slowly than surface currents, thermohaline circulation moves larger volumes of water, and a large amount of heat as well. While thermohaline circulation doesn't have a beginning or end, our discussion starts with the flow of the Gulf Stream toward the Arctic Ocean (Fig. 3.22). When this warm water mixes with the cold water of the Arctic Ocean, it cools, increases in density, and sinks. In addition, some water forms sea ice, leaving the salt behind to make the ocean water more saline, also increasing its density. As the cold temperature and increased salinity cause denser water to sink, surface water moves to replace the sinking water, forming a current and driving the thermohaline circulation. This process also occurs in the southern hemisphere as warm equatorial surface currents meet cold Antarctic waters. As this water moves northward, it warms; feeding the warm, shallow currents in the Indian Ocean and North Pacific.

Describe the deep thermohaline circulation of Earth's oceans.

The circulation systems of the atmosphere and the oceans are intimately connected, because the major driving force for ocean currents is the frictional drag of the winds on the surface of the ocean. Ocean currents are driven by the winds flowing out of the subtropical high-pressure cells in both hemispheres (Fig. 3.20). As wind moves over the rough ocean surface, the resulting friction transfers energy from the wind to the water, causing the water to move. This main force is modified by the Coriolis force, density differences caused by temperature and salinity, the configuration of the continents and ocean floor, and astronomical forces that cause the tides. Because ocean currents flow over long distances, the Coriolis force deflects them.

Describe the forces that create surface ocean currents.

- High pressure is associated with descending and diverging air, and low pressure is associated with converging and ascending air. Surface friction decreases both the speed of winds and the Coriolis force. Winds close to the surface result from the pressure-gradient force, the Coriolis force, and friction. The net effect of these forces is wind that flows at a 20° to 45° angle to the pressure gradient (Fig. 3.8). - Northern Hemisphere winds descend and spiral out from a high-pressure area clockwise to form an anticyclone and spiral into a low-pressure area counterclockwise and ascend to form a cyclone. In the Southern Hemisphere, these circulation patterns are reversed, with winds flowing counterclockwise out of anticyclonic high-pressure cells and clockwise into cyclonic low-pressure cells. - Above 500 m (1600 ft), the two forces acting upon wind are the pressure-gradient force and the Coriolis force. Figure 3.8 shows that the result of these two forces is for wind to flow parallel to the isobars. Such winds, called geostrophic winds, are characteristic of upper tropospheric circulation. *video 3.2*

Describe the horizontal and vertical air motions in a high-pressure anticyclone and in a low-pressure cyclone.

- The monsoons are seasonally shifting wind systems caused by the annual cycle of migrating pressure belts. - The location and size of the Asian landmass and its proximity to the Indian Ocean drive the monsoons of southern and eastern Asia (Fig. 3.19). In the winter, high pressure dominates central Asia, while the equatorial low-pressure tough (ITCZ) is over the central Indian Ocean. This pressure gradient produces cold, dry winds from the Asian interior over the Himalayas and across India. These winds dry out the landscape, especially in combination with the hot temperatures from March through May. - The ITCZ shifts northward during June to September, and high temperatures create a thermal low in the Asian interior. Subtropical high pressure dominates the Indian Ocean, with a sea-surface temperature of 30°C (86°F). As a result of this reversed pressure gradient, hot winds pick up moisture from the warm ocean as they flow toward and are lifted by the Himalayas. When the monsoonal rains arrive from June to September, they bring welcome relief from the dust, heat, and parched land of Asia's springtime. World-record rainfalls drench India. Cherrapunji, India, shown on the map, received both the second highest average annual rainfall (1218 cm, or 479.5 in.) and the highest single-year rainfall (2647 cm, or 1042 in.) on Earth.

Describe the seasonal pressure patterns that produce the Asian monsoonal wind and precipitation patterns. Contrast January and July conditions.

- Subpolar gyres form in the polar regions of the planet. They sit beneath an area of low atmospheric pressure. Wind drives the currents in subpolar gyres away from coastal areas. - Most of the world's major gyres are subtropical gyres. These form between the polar and equatorial regions of Earth. Subtropical gyres circle areas beneath regions of high atmospheric pressure.

Do gyres follow the pattern of high- or low-pressure circulation?

The Coriolis force (also called the Coriolis effect) makes wind appear to be deflected in relation to Earth's rotating surface. Because Earth rotates eastward, objects appear to curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere (Fig. 3.7). The Coriolis force is an effect of Earth's rotation.

Explain how the Coriolis force appears to deflect atmospheric and oceanic circulations.

Northern Hemisphere winds descend and spiral out from a high-pressure area clockwise to form an anticyclone and spiral into a low-pressure area counterclockwise and ascend to form a cyclone. In the Southern Hemisphere, these circulation patterns are reversed, with winds flowing counterclockwise out of anticyclonic high-pressure cells and clockwise into cyclonic low-pressure cells. Above 500 m (1600 ft), the two forces acting upon wind are the pressure-gradient force and the Coriolis force. Figure 3.8 shows that the result of these two forces is for wind to flow parallel to the isobars. Such winds, called geostrophic winds, are characteristic of upper tropospheric circulation.

Explain how the pressure gradient, Coriolis, and friction forces affect winds in cyclones and anticyclones.

Air pressure is measured using a barometer. (aneroid and mercury) A wind vane determines wind direction. The standard measurement is taken 10 m (33 ft) above the ground to reduce surface effects on wind direction Winds are named for the direction from which they originate (Fig. 3.5). For example, a north wind blows from the north to the south. The most common winds in the midlatitudes are called the westerlies, because they blow from the west toward the east.

Explain how wind is measured, how wind direction is determined, and how winds are named.

ridges + troughs: - Upper-air maps include areas of high pressure called ridges and areas of low pressure called troughs. The 500-mb height contours showing a ridge bend poleward; the contours showing a trough bend equatorward. - Ridges and troughs in the upper-air wind flow are important in sustaining surface cyclonic (low-pressure) and anticyclonic (high-pressure) circulation. Winds near the ridges slow and converge, causing air to descend and create high pressure at the surface, whereas winds near the area of maximum wind speeds along the troughs accelerate and diverge, causing low pressure air to converge and ascend from the surface rossby waves: - Within the westerly flow of upper-air winds are Rossby waves (Fig. 3.14). Rossby waves flow along the polar front - The development of Rossby waves begins with ripples along the polar front that increase in amplitude to form waves. The extremely cold conditions during the "polar vortex" of 2014 were due to one of these waves growing in size and extending farther south than usual. These ripples develop into waves of ridges and troughs of higher and lower air pressure. If you live in the midlatitudes, the storms you experience during winter occur along the polar front. jet streams: - The most prominent movements in these upper-level westerly wind flows are the jet streams, migrating rivers of wind that influence surface weather systems (Fig. 3.15). The jet streams are 160-480 km (100-300 mi) wide but only 900-2150 m (3000-7000 ft) thick, with core speeds that can exceed 300 kmph (190 mph). They tend to weaken during summer and strengthen during winter as the streams shift closer to the equator. The pattern of ridges and troughs causes variation in jet stream speeds. - The polar jet stream meanders between 30° and 70° N, at the top of the troposphere, along the polar front, at altitudes between 7600 and 10,700 m (24,900 and 35,100 ft). The polar jet stream can migrate as far south as Texas, steering colder air masses into North America and influencing surface storm paths traveling eastward. In the summer, the polar jet stream exerts less influence on storms by staying over higher latitudes. The subtropical jet stream meanders from 20° to 50° N and may occur over North America simultaneously with the polar jet stream

Explain pressure patterns and winds in the middle and upper troposphere. Describe Rossby waves.

Regional winds are part of Earth's secondary atmospheric circulation. The monsoons are seasonally shifting wind systems caused by the annual cycle of migrating pressure belts. Monsoons occur in the tropics over Southeast Asia, Indonesia, India, northern Australia, and equatorial Africa. A mild version of such a monsoonal-type flow affects the southwestern United States. The location and size of the Asian landmass and its proximity to the Indian Ocean drive the monsoons of southern and eastern Asia (Fig. 3.19). In the winter, high pressure dominates central Asia, while the equatorial low-pressure tough (ITCZ) is over the central Indian Ocean. This pressure gradient produces cold, dry winds from the Asian interior over the Himalayas and across India. These winds dry out the landscape, especially in combination with the hot temperatures from March through May. The ITCZ shifts northward during June to September, and high temperatures create a thermal low in the Asian interior. Subtropical high pressure dominates the Indian Ocean, with a sea-surface temperature of 30°C (86°F). As a result of this reversed pressure gradient, hot winds pick up moisture from the warm ocean as they flow toward and are lifted by the Himalayas.

Explain regional monsoons in relation to Earth's atmospheric circulation.

Ocean currents can move vertically as well as horizontally, because of local winds and differences in temperature, salinity, and density. Upwelling currents are formed where surface water is swept away from a coast. Cool nutrient-rich water rises from great depths to replace the water that was pushed aside.

Explain the causes and effects of upwelling and downwelling.

- Heating differences between land and water produce the land and sea breezes that occur on most coastlines (Fig. 3.16). Land warms faster than the water during the day. The warm air rises because it is less dense, which causes air pressure at the surface to drop by 1-2 mb, which triggers an onshore flow of cooler marine air to replace the rising warm air—usually strongest in the afternoon. - The onshore flow of cooler air can lower the temperature by 2° to 10° C (3.6° to 18° F). At night, land cools faster than the water, cooler air over the land subsides and flows offshore over the warmer water, where the air is lifted. The land breezes are usually not as strong as the sea breezes, because land has a rougher surface than the ocean, so friction reduces the wind speed.

Explain the factors that produce land and sea breezes.

WIND: - Gravity pulls objects, including air molecules, toward the center of Earth. The gravitational force creates air pressure by compressing the atmosphere so that pressure is greatest at Earth's surface, and decreases with altitude. Without gravity, there would be no air pressure, and therefore no wind. PRESSURE-GRADIANT: A pressure gradient is the difference in air pressure between two points on Earth's surface. These pressure differences establish a pressure-gradient force that causes winds by driving air from areas of higher air pressure to areas of lower pressure (Fig. 3.6). Without a difference in air pressure between two locations, there would be no wind. Recall that these high- and low-pressure areas are mainly formed by the unequal heating of Earth's surface. Cold, dense air at the poles exerts greater pressure than warm, less dense air along the equator. CORIOLIS: The Coriolis force (also called the Coriolis effect) makes wind appear to be deflected in relation to Earth's rotating surface. Because Earth rotates eastward, objects appear to curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere (Fig. 3.7). The Coriolis force also increases as the speed of the moving object increases, so faster winds have greater apparent deflection. Without the Coriolis force, winds would move along straight paths between high- and low-pressure areas. FRICTION: The friction force slows wind speeds and reduces Coriolis force close to the surface. Surface friction extends to a height of about 500 m (around 1600 ft). In general, rougher surfaces produce more friction. Because surface friction decreases wind speed, it reduces the effect of the Coriolis force and causes winds to move across isobars at an angle.

Explain the four driving forces within the atmosphere: gravity, pressure gradient force, Coriolis force, and friction force. Briefly describe the four forces that cause winds.

By flying in a jet stream, aircraft travelling from west to east get carried along by the tailwind, saving them time - and/or fuel

How could pilots use the jet stream to their advantage?

EL NINO: - During an El Niño, air pressures and trade winds shift (Fig. 3.23b). Air pressure is higher than usual over the western Pacific and lower than usual over the eastern Pacific. - The change in wind and ocean current direction causes cooler sea-surface temperatures in the western Pacific. At the same time, sea-surface temperatures increase up to 8°C (14°F) above normal in the central and eastern Pacific as warm water replaces the normally cold, nutrient-rich water along Peru's coastline. - Higher air pressure over the western Pacific causes drier conditions, while the lower air pressure over the eastern Pacific is associated with rising air and wetter conditions. LA NINA: - In North America, La Niña brings higher amounts of rainfall across the upper Midwest, the northern Rockies, Northern California, and the Pacific Northwest. Canada typically experiences cooler and snowier winters. South America has drought conditions across Peru and Chile, while northern Brazil receives more rain than normal.

How do conditions in the eastern and western Pacific Ocean differ during El Niño and La Niña?

- climate change may be altering patterns of atmospheric circulation, esp in relation to arctic sea-ice melting and the jet stream, as well as possible intensification of subtropical high-pressure cells - air pollution in Asia affects monsoonal wind flow; weaker flow could reduce rainfall and affect water availability

How do humans impact atmospheric and oceanic circulation?

dry; Broad high-pressure zones of hot, dry air exist in both hemispheres between 20° and 35° latitude. The clear, frequently cloudless skies over the Sahara and the Arabian Deserts are typical of these zones, referred to as the subtropical high or subtropical high-pressure cells. Powered by the Hadley cells and their strong vertical movement of air in the ITCZ, these surface high-pressure cells are characterized by wind diverging at the surface. The high-pressure centers form as air above the subtropics in the Hadley cells is pushed downward and heats by compression on its descent to the surface. Warmer air has a greater water vapor capacity than cooler air, making this descending warm air relatively dry because of its large water vapor capacity compared to its low water vapor content. The air is also dry because of the moisture that was lost as precipitation as the air initially rose in the ITCZ. One of the main reasons for the world's deserts being found in the subtropics is the warm, dry air from the subtropical high-pressure cells. - dry all year long and probably hot all year long

How do the subtropical high-pressure cells affect summer rainfall in California and the Mediterranean? How would those climates be affected if the subtropical high-pressure cells became stronger throughout the year?

El Niño is tied to strong hurricanes in the eastern Pacific and droughts in South Africa, India, Australia, and the Philippines (Figs 3.24a and c). In India, every drought for more than 400 years seems linked to this warm phase of ENSO. In the United States, the Northeast and Midwest states have warmer and drier winters, while the Southwest has cooler and wetter winters. La Niña often brings wetter conditions throughout Indonesia, the South Pacific, and northern Brazil (Fig. 3.24b). During El Niño years Atlantic hurricanes are stronger, and during La Niña years they are weaker. In North America, La Niña brings higher amounts of rainfall across the upper Midwest, the northern Rockies, Northern California, and the Pacific Northwest. Canada typically experiences cooler and snowier winters. South America has drought conditions across Peru and Chile, while northern Brazil receives more rain than normal.

How does the ENSO affect your weather? Explain the effects during the El Niño and La Niña phases of the ENSO.

Winds near the ridges slow and converge, causing air to descend and create high pressure at the surface, whereas winds near the area of maximum wind speeds along the troughs accelerate and diverge, causing low pressure air to converge and ascend from the surface

How does upper-level convergence affect surface air flow?

- We use this 500-mb level to analyze upper-air winds and how they might affect surface weather conditions. Just as with surface maps, closer spacing of the isobars indicates faster winds; wider spacing indicates slower winds. Upper-air maps include areas of high pressure called ridges and areas of low pressure called troughs. The 500-mb height contours showing a ridge bend poleward; the contours showing a trough bend equatorward. - Ridges and troughs in the upper-air wind flow are important in sustaining surface cyclonic (low-pressure) and anticyclonic (high-pressure) circulation. Winds near the ridges slow and converge, causing air to descend and create high pressure at the surface, whereas winds near the area of maximum wind speeds along the troughs accelerate and diverge, causing low pressure air to converge and ascend from the surface.

How is the 500-mb surface, especially the ridges and troughs, related to surface pressure systems? How are upper-level divergence and surface lows related? Convergence aloft and surface highs?

The surface wind is the balance of forces on the wind that occurs at and near the Earth's surface. The contrast to the geostrophic wind is that it is the product of the Pressure-gradient force and the Coriolis force, surface winds introduce friction.

How is the flow of geostrophic winds different from the flow of surface winds?

Just as a ball rolls down a steep hill more quickly than a gently sloped hill, a steeper pressure gradient generates higher winds than a less-steep pressure gradient.

How is the pressure-gradient force related to wind speed?

Studies show that warming Arctic temperatures and melting polar ice could disrupt the deep current in the North Atlantic. Vast areas of melting sea ice and land ice, as in Greenland, are adding fresh water to the Arctic Ocean. Because the fresh water is less dense than salt water, these changes could affect the rate of sinking, and slow or stop the North Atlantic deep ocean circulation.

How would a warmer Arctic affect thermohaline circulation?

They tend to weaken during summer and strengthen during winter as the streams shift closer to the equator.

In which season is the polar jet stream strongest?

gyres

Large, rotating ocean currents. They are driven by prevailing winds and the Coriolis force

Warmer, less-dense air along the equator rises, creating the *low pressure* region of the intertropical convergence zone or ITCZ; and colder, more-dense air at the poles sinks, creating the weak polar *high-pressure* cells. Air sinking over the tropics creates the subtropical *high-pressure* cells, and warm air moving poleward from the tropics rises, creating the subpolar *low-pressure* cells PRINCIPAL WINDS: - Air sinking to the surface spreads out and flows both toward the poles and toward the equator, creating two important belts of winds. In both hemispheres, winds are generally easterly (westward-moving) toward the equator from the tropics, and they are generally westerly (eastward-moving) in the middle and high latitudes. (subtrop hi press) - In the Northern Hemisphere, the air flowing toward the equator forms the northeast trade winds. - In the Southern Hemisphere, air flowing toward the equator forms the southeast trade winds. - The wind flowing from the subtropical highs toward the poles in both hemispheres is deflected by the Coriolis force to create the westerlies, the main winds in the midlatitudes. The westerlies initially flow toward the pole from the subtropical high, but they are deflected to flow from the west as they move toward the poles.

Locate the primary high- and low-pressure areas and principal winds. Where are the four bands of pressure in each hemisphere? Describe the two wind systems created by the subtropical high-pressure cells.

Coriolis force

The apparent deflection of moving objects (wind, ocean currents, missiles) from traveling in a straight path, in proportion to the speed of Earth's rotation at different latitudes. Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere; maximum at the poles and zero along the equator.

friction force

The effect of drag by the wind as it moves across a surface; may be operative through 500 m (1600 ft) of altitude. Surface friction slows the wind and therefore reduces the effectiveness of the Coriolis force.

wind

The horizontal movement of air relative to Earth's surface; produced essentially by air pressure differences from place to place; turbulence, wind updrafts and downdrafts, adds a vertical component; its direction is influenced by the Coriolis force and surface friction.

jet streams

The most prominent movement in upper-level westerly wind flows; irregular, concentrated, sinuous bands of geostrophic wind, traveling at 300 kmph

western intensification

The piling up of ocean water along the western margin of each ocean basin, to a height of about 15 cm (6 in.); produced by the trade winds that drive the oceans westward in a concentrated channel.

westerlies

The predominant surface and aloft wind-flow pattern from the subtropics to high latitudes in both hemispheres.

northeast trade winds

The prevailing northeast winds flowing from the subtropical high toward the ITCZ.

southeast trade winds

The prevailing southeast winds flowing from the subtropical high toward the ITCZ.

La Niña

The weaker, cold-water phase of the El Nino Southern Oscillation. Sea-surface temperatures decrease by at least 0.4° C (0.7° F) below normal in the central and eastern Pacific

Hadley cells

Two circulation cells on either side of the equator. Air rises in the ITCZ, flows toward the poles, sinks over subtropical high, and flows toward the ITCZ.

polar easterlies

Variable, weak, cold, and dry winds moving away from the polar region; an anticyclonic circulation.

- wind energy is a renewable resource that is expanding in use - ongoing climate change may affect ocean currents, including the thermohaline circulation

What are some atmospheric and oceanic circulation impacts of the 21st century?

speed and direction

What are the two main properties of wind that we measure?

Air molecules in the atmosphere are pulled toward the center of Earth by gravity. The molecules bounce off each other, creating air pressure through their motion and number. Air molecules exert more force when they are closer together, as at Earth's surface, or when the temperature is higher and they are moving more quickly. Recall from Chapter 1 that air pressure decreases with altitude. In addition, air pressure rises and falls as weather systems move across Earth's surface

What causes air pressure?

Upwelling currents are formed where surface water is swept away from a coast. Cool nutrient-rich water rises from great depths to replace the water that was pushed aside. These currents exist off the Pacific coasts of North and South America and the subtropical and midlatitude west coast of Africa. These areas are some of Earth's prime fishing regions

Where on Earth are upwelling currents experienced? How are upwelling currents related to fishing conditions?

While thermohaline circulation doesn't have a beginning or end, our discussion starts with the flow of the Gulf Stream toward the Arctic Ocean (Fig. 3.22). When this warm water mixes with the cold water of the Arctic Ocean, it cools, increases in density, and sinks. In addition, some water forms sea ice, leaving the salt behind to make the ocean water more saline, also increasing its density. As the cold temperature and increased salinity cause denser water to sink, surface water moves to replace the sinking water, forming a current and driving the thermohaline circulation.

What causes surface water to sink and form the deep currents of thermohaline circulation?

The Coriolis force is an effect of Earth's rotation

What causes the Coriolis force?

**cool and moist** - The area of contrast between cold, dry air from the polar and Arctic regions and warm, moist air brought by the westerlies forms the polar front, where masses of air with different characteristics battle, bringing storms and rain. This front encircles Earth, centered around these low-pressure areas. - The changing weather patterns in the midlatitudes that we experience are made by secondary highs and lows along the polar front that migrate north and south with the seasons. Low-pressure cyclonic storms, hundreds to thousands of kilometers in diameter, migrate out of the Aleutian and Icelandic frontal areas, bringing precipitation to North America and Europe, respectively. Northwestern sections of North America and Europe generally are cool and moist as a result of the passage of these cyclonic systems.

What climate type is associated with the subpolar low-pressure cells?

**hot and dry** - Broad high-pressure zones of hot, dry air exist in both hemispheres between 20° and 35° latitude. The clear, frequently cloudless skies over the Sahara and the Arabian Deserts are typical of these zones, referred to as the subtropical high or subtropical high-pressure cells. - The pattern of air rising in the ITCZ, moving toward the poles, and sinking in the subtropics creates the Hadley cells, two circulation cells on either side of the ITCZ. Powered by the Hadley cells and their strong vertical movement of air in the ITCZ, these subtropical surface high-pressure cells are characterized by wind diverging at the surface. The high-pressure centers form as air above the subtropics in the Hadley cells is pushed downward and heats by compression on its descent to the surface. - Warmer air has a greater water vapor capacity than cooler air, making this descending warm air relatively dry because of its large water vapor capacity compared to its low water vapor content. The air is also dry because of the moisture that was lost as precipitation as the air initially rose in the ITCZ. One of the main reasons for the world's deserts being found in the subtropics is the warm, dry air from the subtropical high-pressure cells. - Air sinking to the surface spreads out and flows both toward the poles and toward the equator, creating two important belts of winds (northeast trade winds and southeast trade winds)

What climate type is associated with the subtropical high-pressure cells? Explain two reasons that the subtropical highs create the dry conditions that are associated with desert climates.

Differences in density caused by differences in temperatures and salinity produce deep currents called thermohaline circulation (thermo- refers to temperature and -haline refers to salinity, or the amount of salts dissolved in water). Although these currents flow more slowly than surface currents, thermohaline circulation moves larger volumes of water, and a large amount of heat as well.

What is meant by deep-ocean thermohaline circulation? At what rates do these currents flow?

Normal sea-level pressure is 1013.2 mb (millibar, which expresses force per square meter of surface area) 760 mm 29.92 in. of mercury

What is normal sea-level pressure in millibars? In millimeters? In inches?

- Constant high Sun altitude and 12-hour days make large amounts of energy available in the ITCZ throughout the year. - Warm, moist air rises and cools, releasing latent heat and producing condensation and rainfall. **warm and rainy** - Vertical cloud columns frequently reach the top of the troposphere. The combination of heating and convergence forces air aloft and forms the ITCZ. The ITCZ is identified by bands of clouds - The rising air causes surface winds to converge along the entire region of low pressure.

What is the general weather pattern caused by the ITCZ?

the polar front, where masses of air with different characteristics battle, bringing storms and rain. This front encircles Earth, centered around these low-pressure areas. The changing weather patterns in the midlatitudes that we experience are made by secondary highs and lows along the polar front that migrate north and south with the seasons. Low-pressure cyclonic storms, hundreds to thousands of kilometers in diameter, migrate out of the Aleutian and Icelandic frontal areas, bringing precipitation to North America and Europe, respectively. Northwestern sections of North America and Europe generally are cool and moist as a result of the passage of these cyclonic systems.

What is the relationship among the Aleutian low and migratory low-pressure cyclonic storms in North America?

Western intensification: piling up of ocean water along western margin of each ocean basin The circular flow of ocean currents transports warm water from the equator to the poles, where the water cools and moves back to the equator. The trade winds drive the ocean surface waters westward along the equator. When these currents reach the eastern shores of the continents, water actually piles up to an average height of 15 cm (6 in.). This phenomenon, called the western intensification, forms poleward-moving currents.

What is western intensification? How is it related to warm surface currents?

1065 mb (31.43 in.) in Barrow, AK

What was the highest air pressure measured in the US? Where was the lowest air pressure in the US measured?

882 mb (26.02 in.) hurricane wilma (atlantic/caribbean)

What was the lowest air pressure measured in the US? Where was the lowest air pressure in the US measured?

June to September

When is the rainy season in the Asian monsoon?

Rossby waves flow along the polar front

Where do Rossby waves occur?

Santa Ana winds or Land and Sea Breezes location wise -- Strong, dry winds sometimes flow across the desert towards Southern California coastal areas. These Santa Ana winds occur when high pressure builds over the Great Basin of the western United States in the fall, with low-pressure offshore; california borders the pacific also logistics; summer and heat are good factors for land/sea breezes and california tends to be very hot in the summer; santa ana winds are very strong

Which local wind would be best suited to power the electrical demand of air conditioning for California?

In the winter, high pressure dominates central Asia, while the equatorial low-pressure tough *(ITCZ)* is over the central Indian Ocean. This pressure gradient produces cold, dry winds from the Asian interior over the Himalayas and across India. These winds dry out the landscape, especially in combination with the hot temperatures from March through May. *Subtropical high pressure* is above Indian Ocean during wet seasons/summer; The ITCZ shifts northward during June to September, and high temperatures create a thermal low in the Asian interior. Subtropical high pressure dominates the Indian Ocean, with a sea-surface temperature of 30°C (86°F). As a result of this reversed pressure gradient, hot winds pick up moisture from the warm ocean as they flow toward and are lifted by the Himalayas.

Which two pressure systems create the wet and dry seasons of the Asian monsoon?

cold, dry air from the polar and Arctic regions and warm, moist air brought by the westerlies

Which two wind systems combine to create the pattern of weather along the polar front?

Katabatic winds involve the flow of cold, dense air under the influence of gravity, not necessarily pressure differences; Gravity winds are not specifically related to the pressure gradient.

Why are katabatic winds not necessarily related to the pressure gradient?

Normally, the current flowing eastward away from the west coast of South America creates an upwelling of cold water. During an ENSO, the wind and warm surface waters flow toward the South American coast slowing the upwelling currents of nutrient-rich water. This loss of nutrients affects the entire marine food chain, from plankton to birds and seals that feed on fish.

Why does an El Niño reduce upwelling off the coast of South America?

Because Earth rotates eastward, objects appear to curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere

Why does the Coriolis force deflect objects to their left in the Southern Hemisphere?

Gravity pulls objects, including air molecules, toward the center of Earth. The gravitational force creates air pressure by compressing the atmosphere so that pressure is greatest at Earth's surface, and decreases with altitude.

Why is air pressure higher closer to the surface?

Of the two polar regions, the Antarctic has the stronger and more persistent high-pressure system, the Antarctic high, that forms over the Antarctic landmass. When an Arctic polar high-pressure cell does form, it tends to locate over the colder northern continental areas in winter (the Canadian or Siberian high) rather than directly over the relatively warmer Arctic Ocean. Weak because the polar atmosphere receives little energy from the Sun.

Why is the Antarctic high stronger than the Arctic high?

trade winds

Winds from the northeast and southeast that converge in the equatorial low-pressure trough, forming the intertropical convergence zone.

summer; the sea breezes are stronger than in winter because of the large temperature differences between land and ocean water that time of year. Heating differences between land and water produce the land and sea breezes that occur on most coastlines (Fig. 3.16). Land warms faster than the water during the day. The warm air rises because it is less dense, which causes air pressure at the surface to drop by 1-2 mb, which triggers an onshore flow of cooler marine air to replace the rising warm air—usually strongest in the afternoon. The onshore flow of cooler air can lower the temperature by 2° to 10° C (3.6° to 18° F). At night, land cools faster than the water, cooler air over the land subsides and flows offshore over the warmer water, where the air is lifted.

Would sea-breezes be stronger during winter or summer? Explain.

pressure

gradient force - Causes air to move from an area of higher barometric pressure to an area of lower barometric pressure due to the pressure difference.