Visibility

Question 1

Visibility difference between fog and mist:

Fog -

Mist -

Answer 1

Vis less than 1 000m

Vis between 1 000m and 5 000m

Question 2

Radiation fog:

Principle -

Favourable conditions(three points) -

The effect of strong wind -

Answer 2

During clear nights when terrestrial radiation is a maximum, air close to the surface will be cooled by contact(because the surface is losing heat quickly)and, provided the dew point is not too low, condensation will take place. If there is no wind dew will form, fog occurs if the dew point is below zero.

a. High relative humdity
b. Clear night for maximum terrestrial radiation
c. Light wind(2 - 8kts)

Radiation fog will lift to low stratus, where it will be burned of by the sun. But in very cold regions where to sun rays are oblique, radiation fog may development thick banks of fog.

Question 3

Advection fog:

Principle -

One prominent characteristic which sets it apart from radiation fog -

Answer 3

Advection will occur anytime warm moist air moves over a cold surface. It tends to form because of the wind, but not when the wind is too strong. This type usually occurs over the sea, where a warm moist air mass blows over the cold Benguella currents, being especially common on the west coast of South Africa.

Advection fog is usually must deeper than radiation fog at times as deep as 2 000ft.

Question 4

Explain Upslope Fog:

Answer 4

When terrain gradually slopes upwards, fog will form due to air being cooled adiabatically as it ascend to a higher altitude. Natal midlands is a prime example of upslope fog.

Question 5

Explain Valley Fog:

Answer 5

When a katabatic wind blows downwards into a valley or basin. The temperature eventually attains dew point.

Question 6

When flying through mist or haze the oblique visibility will -

Answer 6

improve with altitude, and reduce when descending

Question 7

Between looking up into the sun and down into the sun, which will provide greater glare visibility -

Answer 7

Looking down into the sun