Weather Information : A - Nature Of The Atmosphere Flashcards
State the general characteristics in regard to the flow of air around high and low pressure systems in the Northern Hemisphere.
Low pressure—inward, upward, and counterclockwise.
High pressure—outward, downward, and clockwise.
AC 00-6
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?
A low-pressure system is characterized by rising air, which is conducive to cloudiness, precipitation and bad weather.
A high-pressure system is an area of descending air which tends to favor dissipation of cloudiness and good weather.
(AC 00-6)
Describe the different types of fronts (4).
Cold front — a mass of cold, dense, and stable air advances and replaces a body of warmer air.
Occluded front — a fast-moving cold front catches up with a slow-moving warm front. Two types: cold front occlusion and warm front occlusion.
Warm front — The boundary area formed when a warm air mass contacts and flows over a colder air mass.
Stationery front — When the forces of two air masses are relatively equal, the front that separates them remains stationary and influences the local weather for days. The weather is typically a mixture of both warm and cold fronts.
(AC 00-6)
What are the general characteristics and hazards of the weather a pilot would encounter when operating near a cold front? A warm front?
Cold front — As the front passes, expected weather can include towering cumulus or cumulonimbus, heavy rain accompanied by lightning, thunder and/or hail; tornadoes possible; during passage, poor visibility, winds variable and gusting; temperature/dew point and barometric pressure drop rapidly.
Warm front — As the front passes, expected weather can include stratiform clouds, drizzle, low ceilings and poor visibility; variable winds; rise in temperature.
(FAA-H-8083-25)
What is a trough?
A trough (also called a trough line) is an elongated area of relatively low atmospheric pressure. 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; it must go upward. Therefore, a low or trough is an area of rising air. Rising air is conducive to cloudiness and precipitation; hence the general association of low pressure and bad weather. (AC 00-6)
What is a ridge?
A ridge (also called a ridge line) is an elongated area of relatively high atmospheric pressure. Air moving out of a high or ridge depletes the quantity of air; therefore, these are areas of descending air. Descending air favors dissipation of cloudiness; hence the association of high pressure and good weather. (AC 00-6)
What are the standard temperature and pressure values for sea level? (AC 00-6)
59°F or 15°C and 29.92” Hg or 1013.2 millibars.
What are isobars? (AC 00-6)
An isobar is a line on a weather chart which connects areas of equal or constant barometric pressure.
If the isobars are relatively close together on a surface weather chart or a constant pressure chart, what information will this provide? (AC 00-6)
The spacing of isobars on these charts defines how steep or shallow a pressure gradient is. When isobars are spaced very close together, a steep pressure gradient exists which indicates higher wind speeds. A shallow pressure gradient (isobars not close together) usually means wind speeds will be less.
What is the name of the force that deflects winds to the right in the northern hemisphere and left in the southern hemisphere? (AC 00-6)
The Coriolis force. It is at a right angle to wind direction and is directly proportional to wind speed.
Why do surface winds generally flow across the isobars at an angle? (AC 00-6)
Surface friction
At what rate does atmospheric pressure decrease with an increase in altitude? (AC 00-6)
1” Hg per 1,000 feet
What does dew point mean? (AC 00-6)
Dew point is the temperature to which a sample of air must be cooled to attain the state of saturation.
When temperature and dew point are close together (within 5°), what type of weather is likely? (AC 00-6)
Visible moisture in the form of clouds, dew, or fog. Also, these are ideal conditions for carburetor icing.
What factor primarily determines the type and vertical extent of clouds? (AC 00-6)
The stability of the atmosphere.