Questions and Answers
What is the primary reason why air pressure is often overlooked by the general public?
What is the standard unit of atmospheric pressure used in the US since 1940?
What is the purpose of a mercury barometer?
What is the name of the instrument that provides a continuous record of pressure changes over time?
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What is the primary reason for the horizontal movement of air?
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What happens to objects if air pressure is not equal in all directions?
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What is the average air pressure at sea level in millibars?
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What is the term used to describe the horizontal movement of air?
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What is the primary force that generates wind?
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What do closely spaced isobars on a weather map indicate?
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What is the Coriolis effect?
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What is affected by the Coriolis effect?
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Where is the Coriolis effect strongest?
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What is the result of the balance between the pressure-gradient force and the Coriolis effect?
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What is the term for upper-air winds that flow parallel to the isobars?
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What slows down air movement near the Earth’s surface?
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What is the term for fast-moving 'rivers' of air that travel at 75-150 miles per hour?
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What is the effect of friction on wind direction?
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What is the effect of friction on wind speed?
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What is the direction of winds around a low pressure center in the Northern Hemisphere?
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What is the result of horizontal convergence in a low pressure system?
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What type of weather is generally associated with high pressure systems?
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What is the main factor controlling global circulation of air?
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What happens to air as it rises near the equator?
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What is the Coriolis effect?
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What is the result of low pressure on a home barometer?
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What determines the angle of airflow over a surface?
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What happens to air in a high pressure system?
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What happens to air when it reaches 30° N and 30° S?
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What is the name of the large circuit of air that involves the movement of air from the equator to 30° N and 30° S and back to the equator?
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How many large atmospheric circulation cells are present in each hemisphere?
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What is the term used to describe the area where air is moving vertically and surface winds are weak and erratic?
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What is the name of the pattern of wind circulation that changes with the season?
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What is the name of the wind that occurs when cooler air from over the sea moves toward land?
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What is the name of the warm, dry winds that occur on the eastern slopes of the Rocky Mountains?
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What is the name of the wind that occurs in southern California and dramatically increases the likelihood of wildfires in this region?
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What is the process that occurs on the opposite side of the mountain as the air was lifted, resulting in a dry air mass on the leeward side of the mountain?
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What is the term used to describe the winds that occur within the Hadley cell?
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What is the direction indicated by the wind direction measurement?
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What is the instrument used to measure wind speed?
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What happens to the trade winds in the tropical Pacific during an El Nino event?
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What is the term used to describe the change in atmospheric pressure during an El Nino event?
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What is the typical duration of an El Nino event?
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What is the effect of an El Nino event on sea level in the eastern Pacific?
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What is the term used to describe the event that occurs after an El Nino event?
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What is the primary factor that affects the distribution of precipitation?
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What happens to the wind direction in high-pressure regions?
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What is the effect of mountain barriers on precipitation patterns?
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Study Notes
Atmospheric Pressure
- Air pressure is the weight of air above, defined as the pressure exerted by the air column above a unit area
- Average air pressure at sea level is 1 kg/cm² or 14.7 lbs/in²
- This pressure is equivalent to the weight of a 1-square-inch column of water 33 feet high
- Air pressure is measured in units of millibars (mbar), with standard atmospheric pressure at sea level being 1,013.2 mbar
- The term "inches of mercury" is used to describe atmospheric pressure, with a standard pressure of 29.92 inches of mercury
Measuring Atmospheric Pressure
- Mercury barometers are used to measure atmospheric pressure
- They consist of a glass tube filled with mercury, inverted into a dish of mercury
- Changes in atmospheric pressure cause the mercury level to rise or fall
- Aneroid barometers are portable instruments that use a partially evacuated metal chamber to measure pressure changes
- They can be attached to a recording mechanism to provide a continuous record of pressure changes
Wind
- Wind is generated by horizontal differences in air pressure
- Air flows from areas of high pressure to areas of low pressure
- Wind is controlled by three factors:
- Pressure-gradient force
- Coriolis effect
- Friction between moving air and the Earth's surface
- Wind direction is influenced by the Coriolis effect, which causes winds to deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere
Global Atmospheric Circulation
- The concentration of solar energy at the equator affects the atmosphere
- Warm air rises at the equator, moves poleward, and sinks, creating a circulation pattern
- The Coriolis effect deflects moving air, creating large circulation cells in each hemisphere
- There are three atmospheric circulation cells in each hemisphere:
- Hadley Cell (0°-30°)
- Ferrel Cell (30°-60°)
- Polar Cell (60°-90°)
Local Winds
- Sea breeze: occurs when cooler air from over the sea moves toward land
- Land breeze: occurs after sunset when the land cools faster than the sea
- Valley breeze: occurs when air along mountain slopes is heated more intensely than air over the valley floor
- Mountain breeze: occurs after sunset when rapid radiation cooling along the mountain slope occurs
Measuring Wind
- Wind direction is labeled from where it originates (e.g., North wind blows from the north toward the south)
- Wind speed is commonly measured using a cup anemometer
- Prevailing winds are winds that consistently blow more often from one direction than any other
El Niño and La Niña
- El Niño: a complex weather pattern that occurs when the trade winds in the tropical Pacific weaken or reverse direction
- La Niña: a event that occurs after an El Niño event, characterized by strong currents, powerful upwelling, and chilly and stormy conditions along the South American coast
- Both events have significant impacts on global weather patterns and ecosystems
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Description
Learn about the importance of air pressure changes in producing weather conditions, including its relation to hurricane strength. Discover how atmospheric pressure is defined and measured.
