Nature of the Atmosphere (part 3)

Question 1

Is frost considered to be hazardous to flight? Why? (AC00-6)

Answer 1

1. The rough surface of frost spoils the smooth flow of air over an airfoil, therefore causing a slowing of airflow
2. This slowing of the air causes early airflow separation, resulting in a loss of lift
3. Even a small amount of frost on airfoils may prevent an aircraft from becoming airborne at normal takeoff speed

Question 2

What factors must be present for a thunderstorm to form? (AC00-6)

Answer 2

1. Sufficient water vapor
2. An unstable lapse rate
3. An initial upward boost (lifting) to start the storm process in motion

Question 3

What are the three stages of a thunderstorm? (AC00-6)

Answer 3

1. Cumulus stage: Updrafts cause raindrops to increase in size
2. Mature stage: Rain at earth’s surface; it falls through the updrafts; lightning; perhaps roll clouds
3. Dissipating stage: Downdrafts while the rain begins to dissipate

Question 4

What is a temperature inversion? (AC00-6)

Answer 4

1. An inversion is an increase in temperature with height
2. An inversion aloft permits warm rain to fall through cold air below, which could be critical to icing
3. A ground-based inversion favors poor visibility by trapping fog and smoke into low levels of the atmosphere; the air is stable, with little or no turbulence

Question 5

How does fog form? (AC00-6)

Answer 5

1. Fog forms when the temperature and dewpoint of the air become identical (or nearly so)
2. Cooling of the air to a little beyond its dewpoint produces radiation fog, advection fog, or upslope fog
3. Adding moisture and thereby elevating the dewpoint produces frontal fog or steam fog

Question 6

What causes radiation fog to form? (AC00-6)

Answer 6

1. The ground cools the adjacent air to the dew point on calm, clear nights

Question 7

What is advection fog, and where is it most likely to form? (AC00-6)

Answer 7

1. Advection fog results from the transport of warm humid air over a cold surface (primarily along coastal areas during the winter)
2. Unlike radiation fog, it may occur with winds and cloudy skies, at any time of the day or night

Question 8

What is upslope fog? (AC00-6)

Answer 8

1. Upslope fog forms as a result of moist, stable air being cooled as it moves up sloping terrain; Once the upslope wind ceases, the fog dissipates
2. Upslope fog is often quite dense and extends to high altitudes

Question 9

Define the term wind shear, and state the areas in which it is likely to occur? (AC00-6)

Answer 9

1. Wind shear is defined as the rate of change of wind velocity (direction and/or speed); conventionally expressed as vertical or horizontal wind shear
2. It may occur at any level in the atmosphere but three areas are of special concern: low-level temperature inversion, frontal zone or thunderstorm, and Clear air turbulence (CAT) at high levels associated with a jet stream or strong circulation

Question 10

Why is wind shear an operational concern to pilots? (AC00-6)

Answer 10

1. Unexpected changes in wind speed and direction can be very hazardous to aircraft operations at low altitudes on approach and departure from airports

Question 11

What types of weather information will you examine to determine if wind shear conditions might affect your flight? (AC 00-54)

Answer 11

1. PIREPs
2. METARs
3. SIGMETS, and convective SIGMETS
4. Terminal forecasts
5. LLWAS (low level windshear alert system) reports—installed at 110 airports in the U.S.