Driving Forces within the Atmosphere

Question 1

What is Gravitational force?

Answer 1

Four forces determine both speed and direction of winds. The first of these is Earth’s gravitational force, which exerts a virtually uniform pressure on the atmosphere over all of Earth.

Gravity compresses the atmosphere, with the density decreasing as altitude increases. The gravitational force counteracts the outward centrifugal force acting on Earth’s spinning surface and atmosphere.

Without gravity, there would be no atmospheric pressure—or atmosphere, for that matter.

Question 2

What is Centrifugal Force?

Answer 2

Centrifugal force is the apparent force drawing a rotating body away from the center of rotation; it is equal and opposite to the centripetal, or “center-seeking,” force.

Question 3

Other then gravitational force, what are the other three forces that affect wind?

Answer 3

The other forces affecting winds are the pressure gradient force, Coriolis force, and friction force. All of these forces operate on moving air and ocean currents at Earth’s surface and influence global wind-circulation patterns.

Question 4

What is Pressure gradient force?

Answer 4

The pressure gradient force drives air from areas of higher barometric pressure (more-dense air) to areas of lower barometric pressure (less-dense air), thereby causing winds.

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

Question 5

What is a gradient?

Answer 5

A gradient is the rate of change in some property over distance. Without a pressure gradient force, there would be no wind.

Question 6

Why do High and Low pressure areas exist?

Answer 6

High- and low-pressure areas exist in the atmosphere principally because Earth’s surface is unequally heated. For example, cold, dry, dense air at the poles exerts greater pressure than warm, humid, less-dense air along the equator.

Question 7

What are High and Low pressure areas associated with on a regional scale?

Answer 7

On a regional scale, high- and low-pressure areas are associated with specific masses of air that have varying characteristics. When these air masses are near each other, a pressure gradient develops that leads to horizontal air movement.

Question 8

How dose vertical air movement create pressure gradients?

Answer 8

In addition, vertical air movement can create pressure gradients. This happens when air descends from the upper atmosphere and diverges at the surface or when air converges at the surface and ascends into the upper atmosphere. Strongly subsiding and diverging air is associated with high pressure, and strongly converging and rising air is associated with low pressure. These horizontal and vertical pressure differences establish a pressure gradient force that is a causal factor for winds.

Question 9

What is an isobar?

Answer 9

An isobar is an isoline (a line along which there is a constant value) plotted on a weather map to connect points of equal pressure. The pattern of isobars provides a portrait of the pressure gradient between an area of higher pressure and one of lower pressure. The spacing between isobars indicates the intensity of the pressure difference, or pressure gradient.

Question 10

What do closer isobars denote?

Answer 10

Just as closer contour lines on a topographic map indicate a steeper slope on land and closer isotherms on a temperature map indicate more extreme temperature gradients, so closer isobars denote steepness in the pressure gradient.

Question 11

What dose a steep gradient cause?

Answer 11

A steep gradient causes faster air movement from a high-pressure area to a low-pressure area.

Question 12

What do wider spaced Isobars mean?

Answer 12

Isobars spaced wider apart from one another mark a more gradual pressure gradient, one that creates a slower airflow.

Question 13

What produces movement at right angles to the isobar?

Answer 13

Along a horizontal surface, a pressure gradient force that is acting alone (uncombined with other forces) produces movement at right angles to the isobars, so wind blows across the isobars from high to low pressure.

Question 14

What is Coriolis force

Answer 14

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.

Question 15

How dose the Coriolis effect effect the earths wind?

Answer 15

On a nonrotating Earth, surface winds would move in a straight line from areas of higher pressure to areas of lower pressure. But on our rotating planet, the Coriolis force deflects anything that flies or flows across Earth’s surface—wind, an airplane, or ocean currents—from a straight path. Because Earth rotates eastward, such objects appear to curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Because the speed of Earth rotation varies with latitude, the strength of this deflection varies, being weakest at the equator and strongest at the poles

Question 16

Why dose an airplane have to make constant corrections in its flight path to maintain a “straight” heading

Answer 16

Looking from the surface at the airplane, the surface seems stationary, and the airplane appears to curve off course. The airplane does not actually deviate from a straight path, but it appears to do so because we are standing on Earth’s rotating surface beneath the airplane. Because of this apparent deflection, the airplane must make constant corrections in the flight path to maintain its “straight” heading relative to a rotating Earth

Question 17

What would happen to a plane traveling from the north pole due south if the earth were not rotating?

Answer 17

A pilot leaves the North Pole and flies due south toward Quito, Ecuador. If Earth were not rotating, the aircraft would simply travel along a meridian of longitude and arrive at Quito. But Earth is rotating eastward beneath the aircraft’s flight path.

Question 18

How much does the speed of the earth’s rotation increase at 60° N and 0°?

Answer 18

As the plane travels toward the equator, the speed of Earth’s rotation increases from about 838 km·h−1 at 60° N to about 1675 km·h−1 at 0°. If the pilot does not allow for this increase in rotational speed, the plane will reach the equator over the ocean along an apparently curved path, far to the west of the intended destination

Question 19

What happens for planes flying from east to west?

Answer 19

This effect also occurs if the plane is flying in an east–west direction. During an eastward flight from Vancouver to Gander, in the same direction as Earth’s rotation, the centrifugal force pulling outward on the plane in flight (Earth rotation speed + plane speed) becomes so great that it cannot be balanced by the gravitational force pulling toward Earth’s axis. Therefore, the plane experiences an overall movement away from Earth’s axis, observed as a right-hand deflection toward the equator. Unless the pilot corrects for this deflective force, the flight will end up somewhere further south

Question 20

How does the Coriolis effect affect planes traveling westward?

Answer 20

In contrast, flying westward on a return flight opposite Earth’s rotation direction decreases the centrifugal force (Earth rotation speed – plane speed) so that it is less than the gravitational force. In this case, the plane experiences an overall movement toward Earth’s axis, observed in the Northern Hemisphere as a right-hand deflection toward the pole.

Question 21

What direction dose deflection occur in the north and south Hemisphere?

Answer 21

Note the deflection to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Question 22

Name three factors that affect Coriolis’s effect on earth?

Answer 22

Several factors contribute to the Coriolis force on Earth.
First, the strength of this deflection varies with the speed of Earth’s rotation, which varies with latitude.
Second, the deflection occurs regardless of the direction in which the object is moving and does not change the speed of the moving object.
Third, the deflection increases as the speed of the moving object increases; thus, the faster the wind speed, the greater its apparent deflection.

Question 23

How does the Coriolis force affect wind?

Answer 23

As air rises from the surface through the lowest levels of the atmosphere, it leaves the drag of surface friction behind and increases speed (the friction force is discussed just ahead). This increases the Coriolis force, spiraling the winds to the right in the Northern Hemisphere or to the left in the Southern Hemisphere, generally producing upper-air westerly winds from the subtropics to the poles.

Question 24

How does the Coriolis force affect wind in the upper troposphere?

Answer 24

In the upper troposphere, the Coriolis force just balances the pressure gradient force. Consequently, the winds between higher-pressure and lower-pressure areas in the upper troposphere flow parallel to the isobars, along lines of equal pressure.

Question 25

What is Friction force ?

Answer 25

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

Question 26

How does Friction force affect the wind on the boundary layer?

Answer 26

On the boundary layer, friction force drags on the wind as it moves across Earth’s surfaces but decreases with height above the surface.

Question 27

What would happen to surface winds without friction?

Answer 27

Without friction, surface winds would simply move in paths parallel to isobars and at high rates of speed

Question 28

Study Summery of Physical forces on wind Figure 6.8

Question 29

What is a Geostrophic wind

Answer 29

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.

The combined effect of the pressure gradient force and the Coriolis force on air currents in the upper atmosphere, above about 1000 m. Together, they produce winds that do not flow directly from high to low but flow around the pressure areas, remaining parallel to the isobars

Question 30

What prevents the equilibrium between the pressure gradient and the Coriolis forces near the surface?

Answer 30

Near the surface, friction prevents the equilibrium between the pressure gradient and Coriolis forces that results in geostrophic wind flows in the upper atmosphere. Because surface friction decreases wind speed, it reduces the effect of the Coriolis force and causes winds to move across isobars at an angle. Thus, wind flows around pressure centres form enclosed areas called pressure systems, or pressure cells, as illustrated in Figure 6.8c.

Question 31

How do surface winds interact with high and low pressure areas. How dose it differ in the Northern and Southern Hemisphere?

Answer 31

In the Northern Hemisphere, surface winds spiral out from a high-pressure area in a clockwise direction, forming an anticyclone, and spiral into a low-pressure area in a counterclockwise direction, forming a cyclone (Figure 6.8). 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.

Question 32

How dose air behave in anticyclones and cyclones?

Answer 32

Anticyclones and cyclones have vertical air movement in addition to these horizontal patterns. As air moves away from the centres of an anticyclone, it is replaced by descending, or subsiding (sinking), air. These high-pressure systems are typically characterised by clear skies. As surface air flows toward the centres of a cyclone, it converges and moves upward