Geology Ch. 18 - Winds

From what direction does a northeast wind blow? Toward what direction does a south wind blow?

A northeast wind blows from the northeast. A south wind blows toward the north.

What force is responsible for generating wind?

Pressure gradient force

List the factors that combine to direct horizontal airflow (wind).

Pressure gradient force, Coriolis effect, and friction with Earth's surface.

With which global pressure belt are the rain forests of Africa's Congo basin associated? Which pressure system is linked to the Sahara Desert?

The equatorial low is associated with the Congo and the subtropical high is linked to the Sahara.

Describe the operating principles of the mercury barometer and the aneroid barometer.

The mercury barometer consists of a tube filled with mercury inverted into a dish of mercury. Mercury flows out of the tube to balance the weight of the mercury column by the pressure exerted on the mercury in the dish. The aneroid barometer has a partly evacuated vacuum chamber that compresses as the pressure increases. Levers are connected to the chamber and transmit readings to a pointer on a dial that is calibrated to read the correct atmospheric pressure.

Referring to the idealized model of atmospheric circulation, in which belt of prevailing winds is most of the United States?

Westerlies

Which prevailing belts converge in the stormy region known as the polar front?

Westerlies and polar easterlies

What is standard sea-level pressure in millibars, in inches, and in pounds per square inch?

1013.25 millibars, 29.9 inches, and 14.7 pounds per square inch.

Explain the seasonal change in winds associated with India. What term is applied to this seasonal wind shift?

As the land surface heats up in summer, it generates a thermal low pressure. Air from the relatively high-pressure region over the ocean blows into this thermal low. This is called the monsoon.

Unlike winds aloft, which blow nearly parallel to the isobars, surface winds generally cross the isobars. Explain what causes this difference.

At the surface, friction affects wind and as a result alters its direction. The pressure gradient force and the Coriolis effect at the surface causes air to move across the isobars. Aloft, geostrophic winds lack friction with Earth's surface and can travel more quickly as the Coriolis effect balances the PGF.

Does a land breeze blow toward or away from the shore?

Away.

What are the two basic wind measurements? What instruments are used to make these measurements?

Direction and speed. A wind vane is used to measure direction and an anemometer is used to measure speed.

For a surface low-pressure center to exist for an extended period, what condition must exist aloft?

Divergence of air.

Describe the formation of a sea breeze.

During the summer solar radiation heats the land surface near the sea more quickly than it heats water with its high thermal inertia. A thermal low pressure develops over the land, and air flows onto the land from the sea, which is at a relatively higher pressure.

Describe how an El Niño event might affect the climate in North America during the winter. Describe the same for a La Niña event.

El Niño might cause the southern portion of North America to be wet, with the eastern part also being cool. The northern portion of North America might be warmer. A La Niña might cause the southern portion of North America to be warm and dry and the northern portion to be cool.

Which pressure belt is associated with the equator?

Equatorial low

Briefly describe how the Coriolis effect influences air movement.

In the Northern Hemisphere, the Coriolis effect causes the deflection of the path of a moving object, including moving air, to the right. In the Southern Hemisphere, this deflection is to the left. The effect is greater with increasing latitude.

How does a major La Niña event influence the hurricane season in the Atlantic Ocean?

It increases hurricane activity.

What is a local wind?

It is a small-scale wind produced by a locally-generated pressure gradient.

List two advantages of the aneroid barometer.

It is small and portable, and it can be readily connected to a recording mechanism.

Describe air pressure in your own words.

It is the pressure exerted on Earth's surface due to the weight of the overlying air molecules.

Describe how a major El Niño event tends to affect the weather in Peru and Chile compared to Indonesia and Australia.

It will make Peru and Chile wetter than normal and Indonesia and Australia dryer than normal.

During what time of day would you expect to experience a well-developed valley breeze - midnight, late morning, or late afternoon?

Late afternoon.

The trade winds diverge from which pressure belt?

Subtropical high

What factors, in addition to the distribution of wind and pressure, influence the global distribution of precipitation?

Temperature of the air, distribution of land and water, and mountain barriers

Briefly describe the Southern Oscillation and how it is related to El Niño and La Niña.

The Southern Oscillation is a shift in high and low atmospheric pressures in the eastern and western tropical Pacific Ocean. An El Niño is associated with an increase in surface pressure near Australia and a drop in pressure off the coast of Peru. The opposite occurs with La Niña.

Write a generalization relating the spacing of isobars to wind speed.

The closer together the isobars are, the faster the wind speed.

Describe the sea-surface temperatures on both sides of the tropical Pacific during a La Niña event.

The western Pacific has relatively warm water and the eastern Pacific has relatively cool water.

What general weather conditions are to be expected when the pressure tendency is rising? When the pressure tendency is falling?

When the pressure tendency is rising, weather is expected to be fair or good. When the pressure tendency is falling, stormy or bad weather is expected.