6.1 Which of the following instruments is used to measure atmospheric pressure?

6.1 Which of the following instruments is used to measure atmospheric pressure?
Anemometer Barometer Thermograph Tachometer Hygrometer

6.1 Which of the following instruments is used to measure atmospheric pressure?
Anemometer Barometer Thermograph Tachometer Hygrometer Measuring Air Pressure You may be acquainted with the expression “inches of mercury,” which weather reporters use to describe atmospheric pressure. This expression dates from 1643, when Torricelli, a student of the famous Italian scientist Galileo, invented the mercury barometer. Torricelli correctly described the atmosphere as a vast ocean of air that exerts pressure on us and all things about us. To measure this force, he closed one end of a glass tube and filled it with mercury. He then inverted the tube into a dish of mercury (Figure 6–4). Torricelli found that the mercury flowed out of the tube until the weight of the mercury column was balanced by the pressure exerted on the surface of the mercury by the air above. In other words, the weight of the mercury in the column equaled the weight of a similar-diameter column of air that extended from the ground to the top of the atmosphere. Torricelli noted that when air pressure increased, the mercury in the tube rose; conversely, when air pressure decreased, so did the height of the column of mercury. The length of the column of mercury, therefore, became the measure of the air pressure–“inches of mercury.” With some refinements, the mercury barometer invented by Torricelli remains the standard pressure-measuring instrument.

6.2 With an increase in altitude, air pressure:
Increases at a constant rate Increases at a decreasing rate Decreases at a constant rate Decreases at a decreasing rate Decreases at an increasing rate

6.2 With an increase in altitude, air pressure:
Increases at a constant rate Increases at a decreasing rate Decreases at a constant rate Decreases at a decreasing rate Decreases at an increasing rate Pressure Changes with Altitude The rate at which pressure decreases with altitude is not constant. The rate of decrease is much greater near Earth’s surface, where pressure is high, than aloft, where air pressure is low. A model of the U.S. standard atmosphere, shown in Figure 6–7, depicts the idealized vertical distribution of atmospheric pressure at various altitudes. Near Earth’s surface, air pressure decreases by about 10 millibars for every 100-meter increase in elevation, or about a 1-inch drop of mercury for every 1000-foot rise in elevation. Further, atmospheric pressure is reduced by approximately one-half for each 5-kilometer increase in altitude. Therefore, at 5 kilometers the pressure is 500 millibars, about one-half its sea-level value; at 10 kilometers it is one-fourth, at 15 kilometers it is one-eighth, and so forth. Thus, at the altitude at which commercial jets fly (10 kilometers), the air exerts a pressure equal to only one-fourth that at sea level.

6.3 On an upper-level weather chart, a ridge indicates:
The direction major weather systems are moving An elongated high pressure area An elongated low pressure area A region of cold, wet weather A constant 18,000 foot elevation

6.4 The addition of water vapor into a volume of air will cause the density of air to:
Decrease Increase Stay the same Vary widely in a horizontal direction

6.4 The addition of water vapor into a volume of air will cause the density of air to:
Decrease Increase Stay the same Vary widely in a horizontal direction Pressure Changes with Altitude Influence of Water Vapor on Air Pressure The amount of water vapor contained in a volume of air influences its density. Contrary to popular perception, water vapor reduces the density of air. The air may feel “heavy” on hot, humid days, but it is not. You can easily verify this fact for yourself by examining a periodic table of the elements and noting that the molecular weights of nitrogen (N2) and oxygen (O2) are greater than that of water vapor (H2O). In a mass of air the molecules of these gases are intermixed, and each takes up roughly the same amount of space. As the water content of an air mass increases, lighter water vapor molecules displace heavier nitrogen and oxygen molecules. Therefore, humid air is lighter (less dense) than dry air. Nevertheless, even very humid air is only about 2 percent less dense than dry air at the same temperature.

6.5 Lines of equal pressure are called:
Isotherms Isohyets Isotachs Isodrosotherms Isobars

6.5 Lines of equal pressure are called:
Isotherms Isohyets Isotachs Isodrosotherms Isobars Factors Affecting Wind Pressure Gradient Force Variations in air pressure over Earth’s surface are determined from barometric readings taken at hundreds of weather stations. These pressure measurements are shown on surface weather maps using isobars (iso = “equal”, bar = “pressure”) lines connecting places of equal air pressure (Figure 6–12).

6.6 Winds are generated by the:
Coriolis force Pressure gradient force Friction force Centrifugal force Centripetal force

6.6 Winds are generated by the:
Coriolis force Pressure gradient force Friction force Centrifugal force Centripetal force Factors Affecting Winds Pressure Gradient Force The spacing of the isobars indicates the amount of pressure change occurring over a given distance and is called the pressure gradient force. Pressure gradient is analogous to gravity acting on a ball rolling down a hill. A steep pressure gradient, like a steep hill, causes greater acceleration of a parcel of air than does a weak pressure gradient (a gentle hill).

6.7 On a weather map of air pressure, what can you infer from a closer spacing of isobars?
Nothing can be inferred. A steep pressure gradient and light winds A steep pressure gradient and strong winds A weak pressure gradient and light winds A weak pressure gradient and strong winds

6.7 On a weather map of air pressure, what can you infer from a closer spacing of isobars?
Nothing can be inferred. A steep pressure gradient and light winds A steep pressure gradient and strong winds A weak pressure gradient and light winds A weak pressure gradient and strong winds Factors Affecting Winds Pressure Gradient Force Isobars are lines connecting places of equal atmospheric pressure. The spacing of isobars indicates the amount of pressure change occurring over a given distance—called the pressure gradient force. Closely spaced isobars indicate a steep pressure gradient and high wind speeds, whereas widely spaced isobars indicate a weak pressure gradient and low wind speeds.

6.8 Atmospheric circulations are fundamentally caused by:
The heating of the ozone layer The passage of frontal storm systems Ocean currents Earth’s gravity Unequal heating of Earth’s surface

6.8 Atmospheric circulations are fundamentally caused by:
The heating of the ozone layer The passage of frontal storm systems Ocean currents Earth’s gravity Unequal heating of Earth’s surface Factors Affecting Wind Pressure Gradient Force An important relationship exists between air pressure and temperature. Temperature variations create pressure differences and ultimately wind. Daily temperature differences caused by the unequal heating as in the sea breeze example tend to be confined to a zone only a few kilometers thick. On a global scale, however, variations in the amount of solar radiation received in the polar versus the equatorial latitude generate the much larger pressure systems that in turn produce the planetary atmospheric circulation. Therefore, the underlying cause of global pressure differences and, by extension, wind is mainly the unequal heating of Earth’s land–sea surface.

6.9 In either the Northern or Southern Hemisphere, a cyclonic flow means:
Any clockwise wind flow Any counterclockwise wind flow Circulation around a low pressure center Circulation around a high pressure center Any strong wind

6.9 In either the Northern or Southern Hemisphere, a cyclonic flow means:
Any clockwise wind flow Any counterclockwise wind flow Circulation around a low pressure center Circulation around a high pressure center Any strong wind Factors Affecting Wind Pressure Gradient Force Figure 6–12 is a surface weather map that shows isobars and winds. Wind direction is shown as wind arrow shafts and speed as wind bars (see the accompanying key). Isobars, which reflect pressure patterns, are rarely straight or evenly spaced on surface maps. Consequently, wind generated by the pressure gradient force typically changes speed and direction as it flows. The area of somewhat circular closed isobars represented by the red letter L is a low-pressure system. Low pressure systems that occur in the middle latitudes are called cyclones, or midlatitude cyclones, to differentiate them from tropical cyclones. Midlatitude cyclones tend to produce stormy weather. (Tropical cyclones are also called hurricanes or typhoons, depending on their locations.) In western Canada, a high-pressure system, denoted by the blue letter H, can also be seen. High-pressure areas such as this are called anticyclones. In contrast to cyclones, anticyclones tend to be associated with clearing conditions.

6.10 The Coriolis force occurs because of Earth’s:
Magnetic field Atmosphere Rotation Dense core

6.10 The Coriolis force occurs because of Earth’s:
Magnetic field Atmosphere Rotation Dense core Factors Affecting Wind Coriolis Force Air moves out of the regions of higher pressure and into the regions of lower pressure. However, the wind rarely crosses the isobars at right angles, as the pressure gradient force directs. This deviation is the result of Earth’s rotation and has been named the Coriolis force, after the French scientist Gaspard-Gustave Coriolis, who first expressed its magnitude quantitatively. It is important to note that the Coriolis force cannot generate wind; rather, it modifies airflow.

6.11 In the Northern Hemisphere, the Coriolis force deflects moving air:
To the right To the left Always toward the north Always toward the south It does not deflect moving air.

6.11 In the Northern Hemisphere, the Coriolis force deflects moving air:
To the right To the left Always toward the north Always toward the south It does not deflect moving air. Factors Affecting Wind Coriolis Force The Coriolis force causes all freemoving objects, including wind, to be deflected to the right of their path of motion in the Northern Hemisphere and the left in the Southern Hemisphere. The reason for this deflection can be illustrated by imagining the path of a rocket launched from the North Pole toward a target on the equator (Figure 6–13). If the rocket travels one hour toward its target, Earth would have rotated 15° to the east during its flight. To someone watching the rocket’s path from the location of the intended target, it would look as if the rocket veered off its path and hit Earth 15° west of its target. The true path of the rocket was straight and would appear as such to someone in space looking toward Earth. Earth’s rotation under the rocket produced the apparent deflection. Note that the rocket did not hit its target and as such was deflected to the right of its path of motion because of the counterclockwise rotation of the Northern Hemisphere. Clockwise rotation produces a similar deflection in the Southern Hemisphere, but to the left of the path of motion.

6.12 The Coriolis force is _______ in the upper troposphere because _______.
Enhanced; the pressure gradient is weaker Enhanced; there is less friction Enhanced; there is more friction Decreased; air moves to high latitudes Decreased; there is more friction

6.12 The Coriolis force is _______ in the upper troposphere because _______.
Enhanced; the pressure gradient is weaker Enhanced; there is less friction Enhanced; there is more friction Decreased; air moves to high latitudes Decreased; there is more friction It is common to see “stormy” at the low end of household barometers and “fair” at the high end.

6.13 A geostrophic wind: Flows perpendicular to the pressure gradient force Is usually not affected by the Coriolis force Is strongly influenced by friction Follows the pressure gradient force Flows in the geosphere

6.13 A geostrophic wind: Flows perpendicular to the pressure gradient force Is usually not affected by the Coriolis force Is strongly influenced by friction Follows the pressure gradient force Flows in the geosphere Winds Aloft Geostrophic Flow When the Coriolis force is exactly equal in strength but acting in the opposite direction of the pressure gradient force, the airflow is said to be in geostrophic balance. The winds generated by this balance are called geostrophic (“turned by Earth”) winds. Geostrophic winds flow in relatively straight paths, parallel to the isobars (perpendicular to the pressure gradient force), with velocities proportional to the pressure gradient force. A steep pressure gradient creates strong winds, and a weak pressure gradient produces light winds.

6.14 Buys Ballot’s law states that:
In the Northern Hemisphere, low pressure will be on your left if you stand with your back to the wind Winds higher than a few kilometers are called geostrophic Winds at Earth’s surface are frictionless Cyclonic flow must be opposite the direction of Earth’s rotation

6.15 Which of the following is INCORRECT relative to air circulation?
Anticyclone—High pressure Cyclone—Low pressure Anticyclone—Clockwise circulation in the Southern Hemisphere Cyclone—Counterclockwise circulation in the Northern Hemisphere

6.15 Which of the following is INCORRECT relative to air circulation?
Anticyclone—High pressure Cyclone—Low pressure Anticyclone—Clockwise circulation in the Southern Hemisphere Cyclone—Counterclockwise circulation in the Northern Hemisphere Surface Winds We have learned that above the friction layer in the Northern Hemisphere, winds blow counterclockwise around a cyclone and clockwise around an anticyclone, with winds nearly parallel to the isobars. Combined with the effect of friction, we notice that the airflow crosses the isobars at varying angles, depending on the terrain, but always from higher to lower pressure. In a midlatitude cyclone (low), in which pressure decreases inward, friction causes a net flow toward its center (Figure 6–21). In an anticyclone (high), the opposite is true: The pressure decreases outward, and friction causes a net flow away from the center. Therefore, the resultant winds blow into and counterclockwise about a midlatitude cyclone and outward and clockwise about a anticyclone (Figure 6–21). Of course, in the Southern Hemisphere the Coriolis force deflects the winds clockwise and reverses the direction of flow. Regardless of hemisphere, however, friction causes a net inflow (convergence) around a midlatitude cyclone and a net outflow (divergence) around an anticyclone.

6.16 In a Northern Hemisphere cyclone viewed from above, surface winds blow:
Clockwise and parallel to isobars Clockwise and outward Counterclockwise and parallel to isobars Counterclockwise and inward

6.16 In a Northern Hemisphere cyclone viewed from above, surface winds blow:
Clockwise and parallel to isobars Clockwise and outward Counterclockwise and parallel to isobars Counterclockwise and inward Surface Winds Airflow crosses isobars at varying angles, depending on the terrain, but always from higher to lower pressure. In a midlatitude cyclone (low), in which pressure decreases inward, friction causes a net flow toward its center (Figure 6–21). In an anticyclone (high), the opposite is true: The pressure decreases outward, and friction causes a net flow away from the center. Therefore, the resultant winds blow into and counterclockwise about a midlatitude cyclone and outward and clockwise about a anticyclone (Figure 6–21). Of course, in the Southern Hemisphere the Coriolis force deflects the winds clockwise and reverses the direction of flow. Regardless of hemisphere, however, friction causes a net inflow (convergence) around a midlatitude cyclone and a net outflow (divergence) around an anticyclone.

6.17 High air-pressure systems are usually associated with:
Diverging winds at the surface Subsiding air Clear weather All of the above are correct. Only a and c are correct.

6.17 High air-pressure systems are usually associated with:
Diverging winds at the surface Subsiding air Clear weather All of the above are correct. Only a and c are correct. How Winds Generate Vertical Air Motion Vertical Airflow Associated with Midlatitude Cyclones and Anticyclones In an anticyclone, outflow near the surface is accompanied by convergence aloft and general subsidence of the air column (Figure 6–22). Because descending air is compressed and warmed, cloud formation and precipitation are less likely in an anticyclone. Thus, fair weather can usually be expected with the approach of a high-pressure system.

6.18 If “fair” weather is approaching, the pressure tendency would probably be:
Falling Steady Rising Pressure tendency has nothing to do with forecasting fair or stormy weather.

6.18 If “fair” weather is approaching, the pressure tendency would probably be:
Falling Steady Rising Pressure tendency has nothing to do with forecasting fair or stormy weather. How Winds Generate Vertical Air Motion Vertical Airflow Associated with Midlatitude Cyclones and Anticyclones It is common to see “stormy” at the low end of household barometers and “fair” at the high end. By noting the pressure trend—rising, falling, or steady—we have a good indication of forthcoming weather. Such a determination, called the pressure tendency, or barometric tendency, is useful in short-range weather prediction. Because descending air is compressed and warmed in an anticyclone, cloud formation and precipitation are less likely than in a cyclone. Thus, fair weather can usually be expected with the approach of a high-pressure system.

6.19 On a 360 degree wind vane dial, winds from the west are associated with:
0 degrees 90 degrees 180 degrees 270 degrees

6.19 On a 360 degree wind vane dial, winds from the west are associated with:
0 degrees 90 degrees 180 degrees 270 degrees Wind Measurement Sometimes the wind direction is shown on a dial that is connected to the wind vane. The dial indicates the direction of the wind either by points of the compass—that is, N, NE, E, SE, and so on—or by a scale of 0 to 360°. On the latter scale, 0° (or 360°) is north, 90° is east, 180° is south, and 270° is west.

6.20 An instrument used to measure wind speed is called a(n):
Anemometer Aneroid barometer Thermograph Tachometer Hygrometer

6.20 An instrument used to measure wind speed is called a(n):
Anemometer Aneroid barometer Thermograph Tachometer Hygrometer Wind Measurement Wind speed is often measured with a cup anemometer, which has a dial much like the speedometer of an automobile (Figure 6–24a).

6.21 When wind consistently blows more often from one direction than any other, this is called a:
Wind vane Wind rose Prevailing wind Trade wind Converging wind

6.22 What country has the largest wind-generating capacity?
China United States Germany Spain India

6.1 Which of the following instruments is used to measure atmospheric pressure?

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6.1 Which of the following instruments is used to measure atmospheric pressure?

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