Met 4 (Visibility and precipitation) Flashcards
What is super cooling?
Where water droplets cool to below freezing but due to the severe curvature of their shape they do not freeze. They instead freeze on impact with surfaces.
What is the Bergeron process?
In clouds with very low temperatures water vapour can freeze into rapidly growing ice crystals.
What are the 5 precipitation symbols?
(-) Light ( ) Moderate (+) Heavy (VC) In vicinity (SH) Showers
What are the 8 different types of precipitation?
- Rain RA
- Drizzle DZ
- Snow SN
- Snow grains SG
- Ice pellets PL
- Ice crystals IC
- Hail +5mm GR
- Hail -5mm GS
What are the 8 solids in the atmosphere?
- Sand SA
- Dust DU
- Haze HZ
- Smoke FU
- Volcanic ash VA
- Dust/sand swirls PO
- Dust storm DS
- Sand storm SS
What’s RVR?
Indicates the range over which the pilot on the centre line of a runway can expect to see the runway surface markings.
What is IRVR?
Instrumented runway visual range. Automatic, continuous display of RVR values.
At what 3 points is IRVR measured?
Touchdown, Mid-point and Stop-end.
Where is all the Met data displayed to a controller?
ADIS
What increments is visibility reported in?
- 50m up to 800m
- 100m up to 5000m
- 1000m up to 9km
- 9999 when 10km+
What is CAVOK?
Cloud and visibility okay
When can CAVOK be used?
When visibility is 10km+, no cloud below 5000ft or Cb, TCu. No weather significant to aviation.
Define fog (FG)
A suspension of small water droplets reducing visibility below 1000m.
Define mist (BR)
The same as fog except visibility is not less than 1000m.
Define haze (HZ)
A suspension of solid particles of smoke or dust reducing visibility to not less than 1000m where the RH is less than 95%.
What are the 6 fog Met codes?
- Fog FG
- Mist BR
- Shallow fog MIFG
- Fog patches BCFG
- Fog covering part of the aerodrome PRFG
- Fog in the vicinity of aerodrome VCFG
What are the two types of fog?
- Radiation fog
- Advection fog
What are the 5 conditions for the formation of radiation fog?
- Clear sky
- Land surface
- Moist air
- Light wind
- Long night
What 3 ways does radiation fog cleared?
- Solar heating
- Cloud cover
- Increasing wind
What 2 ways dies advection fog formed?
- When warm, moist air is transferred by advection currents to a cold land or sea area.
- The warm air loses heat to the cold surface and fog forms if the cooling is sufficient to saturate the air.
What 4 ways is advection fog dispersed?
- Change of air mass to drier air
- Insulation heating ground above the dew point of air mass.
What is freezing fog?
Fog with a temperature below 0 degrees. Rime ice is deposited on surfaces.
What is shallow fog?
Less than 2m in height over land. Less than 10m in height over sea. More than 1000m visibility over the fog layer.
