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Meteorology > Visibility > Flashcards

Visibility Flashcards

1
Q

What is Runway Visual Range?

A

The range over which the pilot of an aircraft on the centre line of a runway can see the runway surface markings or the light delineating the runway or identifying its centre line.

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2
Q

At what visibility do reasons for the reduction in visibility have to be included?

A

Reason for reductions in Visibility have to be reported when the visibility falls below 5000m

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3
Q

What is Fog?

A

FG

A suspension of small water droplets reducing visibility below 1000m.

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4
Q

What is Mist (BR)?

A

A suspension of small water droplets reducing visibility below 5000m but not less than 1000m.

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5
Q

What is Haze?

A

HZ

A suspension of solid particles of smoke or dust reducing visibility to not less than 1000m where the relative humidity is less than 95%

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6
Q

How does fog differ from cloud?

A

Fog differs from cloud in that the cooling required to produce condensation occurs differently. The cooling producing fog and mist usually arises from radiation, advection or mixing.

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7
Q

What must happen for fog to occur?

A

Air near the ground must be cooled to below it’s dew point for condensation to occur.

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8
Q

What is Radiation Fog?

A

Radiation fog is a result of cooling and condensation in the air near the ground. At night the ground radiates heat out from the earth’s system, and the air close to the ground loses heat by conduction.

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9
Q

What are the main requirements for Radiation Fog?

A

CLEAR SKY
So that the earth will radiate its heat energy.

LAND SURFACE
To rapidly cool and conduct this cooling to the adjacent air.

MOIST AIR
So that the layer contacting the ground will reach its dew point.

LIGHT WIND
2-8kts. To provide the right amount of turbulence.

LONG NIGHT
Allow maximum time for effect to become established.

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10
Q

What determines what will happen to the Radiation Fog?

A

Wind Speed determines what will happen to the condensed air.

No wind - may settle on ground as dew and/or shallow fog.
2 - 8kts - held in suspension, thin layer of fog forms.
Greater than 8kts - turbulence lifts fog to form stratus clouds.

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11
Q

What is Advection Fog?

A

Advective currents transfer warm moist air over a colder surface.

The warm air loses heat to the cold surface and fog forms if the air becomes saturated.

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12
Q

What is hill fog or upslope fog?

A

Caused when moist air is forced to ascend over rising ground and is cooled below its dew point by the process of expansion. Condensation occurs at ground level somewhere along the slope.

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13
Q

What is steam fog?

A

It is localised condensation that resembles steam or a thin layer of thick fog at the water’s surface.

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14
Q

What is sea smoke?

A

It is localised condensation that resembles steam or a thin layer of thick fog at the water’s surface.

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15
Q

What is steam fog or sea smoke caused by?

A

Steam fog or sea smoke is caused by cold, dry air moving over relatively warm water.

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16
Q

What solid particles can obscure visibility?

A

The possibilities are haze (HZ) , sand (SA), dust (DU), smoke (FU) and volcanic ash (VA).

17
Q

When should an obscuration be reported?

A

When visibility is reduced to 5,000 metres or less the type of obscuration should be reported.

18
Q

What is Haze?

A

HZ

Extremely small, dry particles invisible to the naked eye but enough to give the air an opalescent appearance. Occurs when then visibility is less than 5000m and humidity is less than 95%.

19
Q

What is Sand?

A

SA

Particles of hard, broken rock or minerals. low drifting sand should always be reported regardless of the value for horizontal visibility.

20
Q

What is Smoke?

A

FU

Small dry particles produced by combustion.

21
Q

What is Dust?

A

DU

Dust or small particles of sand raised from the ground by wind prior to the time of observation.

22
Q

What is Volcanic Ash?

A

VA

Particles of volcanic ash. Its presence should always be reported regardless of the value for horizontal visibility.

23
Q

What is smoke pollution?

A

In conditions of light winds and a temperature inversion, the atmosphere becomes very stable and traps smoke and industrial pollutants.

These conditions may persist for many days and cause smog associated with large cities such as Los Angeles.

A change of air mass to unstable conditions is required before the pollutants can be carried aloft, dispersed and visibility improved.

24
Q

How is visibility measured in the day time?

A

A meteorological observer estimates horizontal visibility by attempting to identify suitable objects at known distances.

25
Q

How is visibility measured in the night time?

A

A meteorological observer estimates horizontal visibility by attempting to identify suitable lights at known distances. This is then converted into equivalent day time visibility.

26
Q

At what intervals is visibility reported?

A

0 > 500m - 50m Intervals
500m > 5km - 100m Intervals
5km and above - 1km Intervals

27
Q

What is prevailing visibility?

A

This is the greatest visibility value which is reached within at least half the horizon circle or within at least half of the surface of the aerodrome.

28
Q

When is the minimum visibility reported in the METAR?

A

The minimum visibility is also reported with its general direction if it is less than 50% of the prevailing visibility, or if the value is less than 1500m.

29
Q

What is Sky Obscured?

A

VV///

When the sky is obscured due to fog, falling or blowing snow.

30
Q

At what point is RVR normally measured?

A

When the met visibility falls below 1500m.

31
Q

What are the two methods of measuring RVR?

A

Human Observer Method
Instrument Runway Visual Range (IRVR)

32
Q

What equipment does IRVR use?

A

Transmissometers. They calculate how much obscurant is in the air by measuring light.

Meteorology (15 decks)

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