Nature of the Atmosphere (part 1)

Question 1

State the general characteristics in regard to the direction of air around high and low pressure systems in the Northern Hemisphere. (AC00-6)

Answer 1

1. Low pressure: counterclockwise
2. High pressure: clockwise

Question 2

If your route of flight takes you towards a low-pressure system, in general, what kind of weather can you expect? What if you were flying towards a high-pressure system? (AC 00-6)

Answer 2

1. A low-pressure system moves inward and upward, and is conducive to cloudiness, precipitation and bad weather
2. A high-pressure system moves outward and downward, and tends to favor dissipation of cloudiness and good weather

Question 3

Describe the different types of fronts. (AC 00-6)

Answer 3

1. Cold front—Occurs when a mass of cold, dense, and stable air advances and replaces a body of warmer air
2. Warm front—The boundary area formed when a warm air mass flows over a colder air mass
3. Occluded front—A frontal occlusion occurs when a fast-moving cold front catches up with a slow-moving warm front. Two types: cold front occlusion and warm front occlusion
4. Stationery front—When the forces of two air masses are relatively equal, the boundary that separates them remains stationary

Question 4

What are the general characteristics of the weather a pilot would encounter when operating near a cold front? (FAA-H-8083-25)

Answer 4

1. Towering cumulus or cumulonimbus clouds
2. Heavy rain accompanied by lightning, thunder and/or hail
3. Tornadoes possible with winds variable and gusting
4. Temperature/dew point and barometric pressure drop rapidly

Question 5

What are the general characteristics of the weather a pilot would encounter when operating near a warm front? (FAA-H-8083-25)

Answer 5

1. Stratiform clouds with possible rain and/or drizzle
2. Low ceilings and poor visibility
3. Variable winds
4. Rise in temperature

Question 6

What is a trough? (AC00-6)

Answer 6

1. A trough line is an elongated area of relatively low atmospheric pressure
2. At the surface when air converges into a low, it cannot go outward against the pressure gradient, nor can it go downward into the ground; therefore, a trough or a low, is an area of rising air
3. Rising air is conducive to cloudiness and precipitation; hence the general association of low pressure and bad weather

Question 7

What is a ridge? (AC00-6)

Answer 7

1. A ridge (also called a ridge line) is an elongated area of relatively high atmospheric pressure
2. Air moving out of a ridge or a high, flows downward; therefore, these are areas of descending air
3. Descending air favors dissipation of cloudiness; hence the association of high pressure and good weather

Question 8

What are the standard temperature and pressure values for sea level? (AC00-6)

Answer 8

1. 59°F or 15°C
2. 29.92” Hg

Question 9

What are isobars? (AC00-6)

Answer 9

1. An isobar is a line on a weather chart which connects areas of equal or constant barometric pressure

Question 10

If the isobars are relatively close together on a surface weather chart or a constant pressure chart, what information will this provide? (AC00-6)

Answer 10

1. How steep or shallow a pressure gradient is
2. When isobars are spaced very close together, a steep pressure gradient exists which indicates higher wind speeds
3. A shallow pressure gradient (isobars not close together) usually means wind speeds will be less

Question 11

What is the name of the force that deflects winds to the right in the northern hemisphere and left in the southern hemisphere? (AC00-6)

Answer 11

1. The Coriolis force

Question 12

Why do surface winds generally flow across the isobars at an angle? (AC00-6)

Answer 12

1. Surface friction

Question 13

At what rate does atmospheric pressure decrease with an increase in altitude? (AC00-6)

Answer 13

1. 1” Hg per 1,000 feet