Chapter 7 Study Guide

Key Terms

scales of motion: A Doppler radar capable of measuring the turbulent eddies that move with the wind. Because of this, it is able to provide a vertical picture of wind speed and wind direction.

Microscale: The smallest scale of atmospheric motions.

Mesoscale: The scale of meteorological phenomena that range in size from a few km to about 100 km. It includes local winds, thunderstorms, and tornadoes.

synoptic scale: The typical weather map scale that shows features such as high- and low-pressure areas and fronts over a distance spanning a continent. Also called the cyclonic scale.

global scale: The largest scale of atmospheric motion. Also called the planetary scale.

Macroscale: The normal meteorological synoptic scale for obtaining weather information. It can cover an area ranging from the size of a continent to the entire globe

rotor-Turbulent eddies that form downwind of a mountain chain, creating hazardous flying conditions.

wind shear: The rate of change of wind speed or wind direction over a given distance.

clear air turbulence (CAT):Turbulence encountered by aircraft flying through cloudless skies. Thermals, wind shear, and jet streams can each be a factor in producing CAT.

thermal circulation: Air flow resulting primarily from the heating and cooling of air.

sea breeze: A coastal local wind that blows from the ocean onto the land. The leading edge of the breeze is termed a sea-breeze front.

land breeze: A coastal breeze that blows from land to sea, usually at night.

valley breeze: A local wind system of a mountain valley that blows downhill (mountain breeze) at night and uphill (valley breeze) during the day.

mountain breeze: A local wind system of a mountain valley that blows downhill (mountain breeze) at night and uphill (valley breeze) during the day.

katabatic wind: Any wind blowing downslope. It is usually cold.

chinook wind: A warm, dry wind on the eastern side of the Rocky Mountains. In the Alps, the wind is called a Foehn.

Santa Ana wind: A warm, dry wind that blows into southern California from the east off the elevated desert plateau. Its warmth is derived from compressional heating.

Haboob: A dust or sandstorm that forms as cold downdrafts from a thunderstorm turbulently lift dust and sand into the air.

dust devils (whirlwinds): A small but rapidly rotating wind made visible by the dust, sand, and debris it picks up from the surface. It develops best on clear, dry, and hot afternoons.

Monsoon: A name given to seasonal winds that typically blow from different directions during different times of the year, most often during summer and winter.

monsoon wind system: A wind system that reverses direction between winter and summer. Usually the wind blows from land to sea in winter and from sea to land in summer.

general circulation of the atmosphere: Large-scale atmospheric motions over the entire earth.

Hadley cell: A thermal circulation proposed by George Hadley to explain the movement of the trade winds. It consists of rising air near the equator and sinking air near 

30° latitude.

Doldrums: The region near the equator that is characterized by low pressure and light, shifting winds.

subtropical highs: A semipermanent high in the subtropical high-pressure belt centered near 

30° latitude. The Bermuda high is located over the Atlantic Ocean off the east coast of North America. The Pacific high is located off the west coast of North America

trade winds: The winds that occupy most of the tropics and blow from the subtropical highs to the equatorial low.

intertropical convergence zone (ITCZ): The boundary zone separating the northeast trade winds of the Northern Hemisphere from the southeast trade winds of the Southern Hemisphere.

Westerlies: The dominant westerly winds that blow in the middle latitudes on the poleward side of the subtropical high-pressure areas

polar front: A semi permanent, semicontinuous front that separates tropical air masses from polar air masses.

subpolar low: A belt of low pressure located between 50° and 70° latitude. In the Northern Hemisphere, this “belt” consists of the Aleutian low in the North Pacific and the Icelandic low in the North Atlantic. In the Southern Hemisphere, it exists around the periphery of the Antarctic continent.

polar easterlies: A shallow body of easterly winds located at high latitudes poleward of the subpolar low

Bermuda high: A semipermanent high in the subtropical high-pressure belt centered near 

30° latitude. The Bermuda high is located over the Atlantic Ocean off the east coast of North America. The Pacific high is located off the west coast of North America.

Pacific high: A semipermanent high in the subtropical high-pressure belt centered near 

30° latitude. The Bermuda high is located over the Atlantic Ocean off the east coast of North America. The Pacific high is located off the west coast of North America.

Icelandic low: The subpolar low-pressure area that is centered near Iceland on charts that show mean sea-level pressure

Aleutian low: The subpolar low-pressure area that is centered near the Aleutian Islands on charts that show mean sea-level pressure.

Siberian high: A strong, shallow area of high pressure that forms over Siberia in winter.

jet stream: Relatively strong winds concentrated within a narrow band in the atmosphere

subtropical jet stream: The jet stream typically found between 20 degrees and 30° altitude at altitudes between 12 and 14 km.

polar front jet stream: The jet stream that is associated with the polar front in middle and high latitudes. It is usually located at altitudes between 9 and 12 km.

Gulf Stream: A warm, swift, narrow ocean current flowing along the east coast of the United States.     
Upwelling: The rising of water (usually cold) toward the surface from the deeper regions of a body of water.

El Niño: An extensive ocean warming that typically extends westward from the coast of Peru and Ecuador across the eastern tropical Pacific Ocean, with associated atmospheric conditions. El Niño events occur roughly once every 2 to 7 years. (See also ENSO.)

Southern 

Oscillation: The reversal of surface air pressure at opposite ends of the tropical Pacific Ocean that occur during major El Niño events.

ENSO: A semi-cyclic variation in surface air pressure across the tropical Pacific Ocean, together with associated changes in surface winds that can induce either an El Niño or La Niña event.

La Niña: A condition where the surface waters of the central and eastern tropical Pacific Ocean turn cooler than normal, with associated atmospheric conditions.

teleconnections-A linkage between weather changes occurring in widely separated regions of the world.

Pacific Decadal Oscillation (PDO): A reversal in ocean surface temperatures that occurs every 20 to 30 years over the northern Pacific Ocean

Indian Ocean Dipole (IOD): A cyclic shift in sea surface temperatures between the western and eastern Indian Ocean.

North Atlantic Oscillation (NAO): A reversal of atmospheric pressure over the Atlantic Ocean that influences the weather over Europe and over eastern North America.

Arctic Oscillation (AO): A reversal of atmospheric pressure over the Arctic that produces changes in the upper-level westerly winds over northern latitudes. These changes in upper-level winds influence winter weather patterns over North America, Greenland, and Europe.

polar vortex: The semipermanent zone of upper-level low pressure found in the polar regions that is sometimes disrupted or displaced during winter. 

Chapter 7 Study Guide Questions

1. What are the scales of atmospheric motion? (Micro, Meso, Synoptic, Global) Name at least one weather phenomenon associated with each.

   1. Micro: Localized phenomena such as thunderstorms or sea breezes.

   2. Meso: Mesoscale convective systems or tornadoes. Larger-scale phenomena such as tornadoes or hurricanes. Synoptic: Weather systems like cold fronts or warm fronts. Global: Patterns such as El Niño or the jet stream.

   3. Synoptic: Mid-latitude cyclones or anticyclones.

   4. Global: El Niño or the Monsoon.

2. What is thermal circulation? Thermal highs and lows? 

   1. Thermal circulation refers to the large-scale movement of air caused by temperature differences, which create areas of high and low pressure. Thermal highs occur in regions where the air is cooler and denser, leading to higher pressure, while thermal lows develop in warmer areas where the air is less dense, resulting in lower pressure. This circulation pattern plays a crucial role in weather systems, influencing wind patterns and precipitation distribution across different regions.

3. What is the sea-breeze? Land breeze? Understand the structure.

   1. Sea-breeze is a local wind that occurs during the day when the land heats up faster than the sea, causing cooler air from the ocean to move inland, while land breeze is the opposite phenomenon that occurs at night, where the land cools more rapidly than the sea, resulting in cooler air moving from the land toward the ocean. Understanding the structure of these breezes involves recognizing the temperature differences between land and water, as well as the resulting pressure gradients that drive these winds. Additionally, these breezes contribute to local climate variations and can significantly affect coastal weather patterns, leading to increased humidity and precipitation in some areas.

4. Understand the basics of Chinook winds and Santa Ana winds.

   1. Chinook winds are warm, dry winds that descend the eastern slopes of the Rocky Mountains, often resulting in rapid temperature increases in the region. Conversely, Santa Ana winds are strong, hot, and dry winds that occur in Southern California, typically blowing from the inland desert areas toward the coast, leading to increased fire danger and dry conditions. These winds are essential to understanding regional weather patterns, as they can lead to significant changes in temperature and humidity, impacting both ecosystems and human activity.

5. What is the Monsoon? Where do we see it?  What does it produce?

   1. The monsoon is a seasonal wind pattern characterized by a shift in wind direction, which brings heavy rainfall during the summer months. We typically see monsoons in South Asia, particularly in countries like India and Bangladesh, as well as in parts of Africa and Australia. The monsoon produces significant precipitation, which is crucial for agriculture, replenishing water supplies, and influencing local climates.

6. What is the three-cell model? Understand and describe the three cells and how the air flows in them. 

   • The three-cell model is a conceptual framework that explains global wind patterns based on the uneven heating of the Earth's surface. It consists of three distinct cells:

     • Hadley Cell: Located between the equator and approximately 30 degrees latitude, this cell is characterized by warm air rising at the equator, which then cools and descends around 30 degrees, creating trade winds.

     • Ferrel Cell: Situated between 30 and 60 degrees latitude, this cell operates in a more complex manner, where the air flows in the opposite direction to the Hadley Cell, creating prevailing westerlies.

     • Polar Cell: Found from 60 degrees latitude to the poles, this cell features cold air that sinks at the poles and flows towards the equator, which leads to the formation of polar easterlies.

     In this model, the air flows in a continuous cycle, influencing weather patterns and climate across different regions. This interaction between the three cells results in distinct climatic zones, including tropical, temperate, and polar climates, each with its own unique weather characteristics.

7. What is the Hadley Cell Circulation?  Understand the structure.

   • The Hadley Cell is a large-scale atmospheric circulation pattern that occurs between the equator and approximately 30 degrees latitude. In this cell, warm air rises at the equator, where intense solar heating causes it to expand and become less dense. As the air rises, it cools and eventually descends around 30 degrees latitude, creating a high-pressure zone. This descending air leads to the formation of trade winds that blow from east to west in the tropics, contributing to the characteristic weather patterns of tropical climates.

8. What is the ITCZ, Trade Winds and Jet Stream – how are they formed in the Hadley Cell?

   • The Intertropical Convergence Zone (ITCZ) is formed where the trade winds from the Northern and Southern Hemispheres meet, resulting in a band of low pressure that is characterized by rising air and frequent thunderstorms. The trade winds are generated by the Coriolis effect acting on the warm, rising air at the equator, which creates easterly winds that move towards the equator. Meanwhile, the jet stream, a fast-flowing air current located in the upper atmosphere, forms at the boundaries between the warm rising air of the Hadley Cell and the cooler air of higher latitudes, influencing weather patterns across the globe. These three components interact dynamically, with the ITCZ shifting north and south with the seasons, affecting precipitation patterns, while the trade winds help drive ocean currents, and the jet stream plays a crucial role in steering weather systems.

9. How does the ITCZ move between seasons?

   • The ITCZ migrates northward during the Northern Hemisphere's summer months and southward during the winter months, following the sun's zenith point. This seasonal shift causes variations in rainfall distribution, with regions experiencing increased precipitation when the ITCZ is overhead and drier conditions when it moves away.

10. Describe the main features of the polar and subtropical jet streams.

    • The polar jet stream is typically found at higher latitudes and is characterized by its strong winds that can reach speeds of over 100 miles per hour, often influencing the development of storm systems and cold fronts. In contrast, the subtropical jet stream is located at lower latitudes and generally has a smoother flow, playing a significant role in the distribution of moisture and temperature, which can impact weather patterns in the mid-latitudes.

11. Where is the Gulf Stream? What is it?

    • The Gulf Stream is a warm ocean current that originates in the Gulf of Mexico, flows along the eastern coast of the United States, and continues across the Atlantic Ocean towards Europe. It is known for its significant influence on the climate of the regions it passes, contributing to milder winters in Western Europe and affecting weather patterns across the Atlantic.

12. Know the difference between El Nino and La Nina and what a pattern shift means for global weather patterns. 

• El Niño refers to the periodic warming of ocean surface temperatures in the central and eastern Pacific Ocean, which can lead to increased rainfall and warmer temperatures in various regions, while La Niña is characterized by cooler ocean surface temperatures in the same area, often resulting in drier conditions and cooler temperatures in affected regions. A pattern shift, such as the transition between El Niño and La Niña, can have profound effects on global weather patterns, including alterations in storm tracks, precipitation distribution, and temperature anomalies, thereby impacting agriculture, water resources, and disaster preparedness.