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Meteorology > Visibility > Flashcards

Visibility Flashcards

1
Q

Visibility is a measure of?

A

How transparent the atmosphere is to the human eye.

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2
Q

What units is horizontal visibility measured in?

A
  1. Up to 5000m in “Metres”
  2. > 5000m in “Kilometres”
  3. > 10km as “Greater than 10 km”
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3
Q

What units is vertical visibility measured in?

A

Feet

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4
Q

Vertical visibility is only given from ___________ when the sky is obscured

A

a staffed observation.

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5
Q

What is the prevailing visibility?

A

The greatest visibility over more than half the horizon.

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6
Q

When should the minimum visibility be provided alongside the prevailing visibility?

A

Where the min visibility is not prevailing AND the min vis <5000m

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7
Q

What two terms are used to denote visibility on a runway?

A
  1. Runway Visual Range (RVR)
  2. Runway Visibility (RV)
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8
Q

In Australia, which term is used exclusively to denote runway visibility measured by an instrumented system?

A

Runway Visual Range (RVR)

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9
Q

When MAY RV/RVR be reported?

A

When visibility is between 800m and 1500m

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10
Q

When MUST RV/RVR be reported?

A

When visibility is below 800m

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11
Q

Causes of reduced visibility fall into which groups?

A

Hydrometeors - associated with water

Lithometeors - associated with non-aqueous particles

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12
Q

Is the sun’s capacity to affect the ability to discern objects considered when measuring visibility?

A

No

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13
Q

List examples of hydrometeors

A
  • Fog
  • Mist
  • Spray
  • Haze (water)
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14
Q

List examples of lithometeors

A
  • Sand
  • Dust
  • Pollen and Bacteria
  • Smoke Haze
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15
Q

Flight beneath an inversion layer can be _________ with ___________

A
  1. turbulent
  2. poor visibilty
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16
Q

Above inversion the air is?

A

Clear and smooth

17
Q

Define Fog

A

A concentration of water droplets or ice crystals reducing visibility to <1000m

The humidity is close to 100%

18
Q

Define Mist

A

Mist is a concentration of water droplets or ice crystals reducing visibility to >1000m.

Humidity is >90%

19
Q

What is fog caused by?

A

Cooling of air below its dew point temperature.

20
Q

What factors affect how soon fog will form?

A
  • Temp/Dew-point difference
  • Rate of cooling
  • Wind strength
21
Q

What can cause cooling?

A
  • an underlying cold ground or water surface
  • the interaction of two air masses
  • the adiabatic cooling of a moist air mass moving up a slope
  • very cold air overlying a warm water surface
22
Q

What does radiation fog require to form?

A
  • Clear skies – to allow radiation cooling
  • Light winds – to allow mixing of cold air
  • High humidity – moisture content
  • Condensation nuclei
23
Q

Generally, explain what weather phenomena you would expect to see in no wind, light wind & stronger winds.

A
  • No wind – Dew or frost
  • Light wind – Fog/mist
  • Stronger wind <7kts – Low stratus cloud
  • Winds >10kts - Nil
24
Q

What causes the dispersal of radiation fog?

A
  • Earth’s surface heated by the sun
  • Air warms and can absorb moisture
  • Thick fog or cloud above can impede this process
  • Wind increasing mixes and disperses.
25
Q

What is required for Advection Fog to occur?

A
  • Warm air flows over a cool surface
  • Air is cooled below its dew-point
  • Can occur suddenly
  • May be more persistent than radiation fog.
26
Q

What are the elements of sea fog?

A
  • Advection fog that forms over the sea
  • Tropical air moving poleward
  • Moist air from land moving offshore over cooler sea.
27
Q

Explain upslope fog

A
  • Air moving up a slope cools adiabatically
  • If cooled below dew-point fog will form
  • If wind abates, fog will dissipate.
28
Q

Explain frontal fog

A
  • Cloud that extends to surface during passage of a front
  • Air that becomes saturated by precipitation
  • Generally ahead of a warm front but can form with slow-moving cold fronts.
29
Q

Explain steam fog

A
  • Caused by cool air over warm wet surface
  • Over polar oceans it’s sometimes called “Sea smoke”
  • Low-level turbulence and severe icing may be present.
30
Q

Multiple RVR observations are always representative of what?

A

The touchdown zone, midpoint zone, and the roll-out/stop end zone respectively

31
Q

What kinds of aerodromes are likely to have a transmissometer?

A

Aerodromes with precision approach systems

Meteorology (9 decks)

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