Chapter 9 - Notes

Question 1

What is the average air pressure at sea level?

In inches of mercury?

Answer 1

1 kg/cm^{<span>2</span>}

29.92 Inches

Question 2

What is falling pressure often associated with?

Answer 2

Increasing cloudiness and the possibility of of precipitation.

Question 3

At whate rate does the Atmospheric Pressure drop with altitude?

Answer 3

Approximately ¹/₂ for each 5 km

Question 4

How does water vapor influence air density?

Answer 4

As the water content of an air mass increases, lighter water vapor molecules displace heavier nitrogen and oxygen molecules.

Nevertheless, even very humid air is only about 2% less dense than dry air at the same temperature.

Question 5

Does cold, dry air producer higher surface pressure than warm, humid air?

Answer 5

Yes.

Because cold air is composed of slow-moving gas molecules that are packed closly together. Thus, a mass of cold air quite dense and will be labeled a High, **for high barometric pressure, on a weather map. and the opposite is true for warm air, being labeled **Low.

Further, the pressure at the surface will increase when there is a net convergance in a region and decrease when there is a net divergence.

Question 6

What is Wind?

Answer 6

Wind is the result of horizontal differences in air pressure. Air blows from areas of higher pressure to areas of lower pressure.

Question 7

Wind is controlled by a combination of forces, they are:

Answer 7

1. The pressure-gradient force
   
   1. If the Pressure-gradient force was the only force acting on the wind, air would flow directly from areas of higher pressures to areas of lower pressure and the lows would be quickly filled.
2. The Coriolis force
   
   1. The Coriolis force is the deflective effet of Earth’s rotation on all free-moving objects, including the atmosphere and oceans. Deflection is to to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This Deflection is always directed at right angles to the direction of airflow; affects only wind direction, not wind speed; is affected by wind speed (the stronger the wind, the greater the deflecting force); and is strongest at the poles and weakens equatorward becoming nonexistent at the equator.
3. Friction
   
   1. Friction’s effect is negligible above a height of a few kilometers.

Question 8

What is the underlying cause of pressure differences?

Answer 8

Unequal heating of Earth’s land-sea surface.