Visibility Flashcards
What is the meteorological optical range
meteorological optical range is the length of path in the atmosphere required to reduce the luminous flux
Visibility, meteorological visibility (by day) and meteorological visibility at night are defined as
the greatest distance at which a black object of suitable dimensions (located on the ground) can be seen and recognized when observed against the horizon sky during daylight
Fog is the only thing that reduces vis below ___m
1000m
Mist will have vis between ____ and ____
1000m and 5000m
Ideal conditions for radiation fog formation:
High relative humidity
Light winds (2 – 8 kts)
Clear skies, long nights
Fog is found in what systems
Prevailing conditions found in high pressure system or col over land
Radiation fog
Radiation fog often clears during the early morning
Temperature increases above the due point
Wind: mixing dry and saturated air
May lift into a low stratus or stratocumulus
Advection fog
Warmer air moving over colder surface
Cold dry air over a warm moist surface can create
Steam fog (sea smoke)
Frontal fog
The warm front approaches and clouds get lower and lower. Eventually they can touch the ground.
Can be 200nm ahead of the warm front
What kind of fog occurs around the caps of hills / mountains?
Hill / up-slope fog
Air is forced up and cools adiabatically
when the due point is reached, a cloud will form
Freezing Fog
FZFG
Fog at a temperature below freezing.
It will normally remain in liquid form, supercooled droplets.
The freezing fog droplets freeze readily on impact with a cold surface.
Ice fog is caused by
For Ice Fog to form temperatures must be very cold, below -35C. Consists of tiny ice crystals suspended in air.
FZFG is supercooled droplets which can cause rime ice when in contact with surfaces below 0C.
Shallow Fog & Mist (MIFG)
If the FG or BR is less than 2m in depth it is defined as shallow (MI).
BCFG
If the fog is occurring in random patches than BCFG is used.
PRFG
If part of the airport is covered (due to proximity of a lake for example) it is called partial fog (PRFG)
Radiation FG:
over land, clear skies, light wind, high humidity
Advection FG:
warm air mass blown over cool surface, high humidity
Frontal FG:
ahead of warm front, cool air saturated due Ns rainfall
Arctic Sea Smoke:
High latitudes, Cold air over warmer water
Ice Fog:
High latitudes, temp below -35C, sublimation Freezing Fog: Supercooled droplets, rime ice
Visibility in cloud
Low level
Low level (NS, ST, Sc, Cu, Cb) - between 10m and 30m
Visibility in cloud
Mid-level
Mid-level (As, Ac) – between 20m and 1000m
Visibility in cloud
High level
High level (Ci, Cs, Cc) – more than 1000m
