Aviation weather Flashcards
Give some characteristics of high pressure (5)
Fairer weather and lighter winds
Moves clockwise around high
Slow moving (couple days)
Air sinks so warming and therefore less chance of hitting dew point
Clear skies so can bring cold weather during winter
Give some characteristics of low pressure
Cloudy poor weather with strong winds
Low moves in anticlockwise direction
Thermal low (5)
Intense heating overland*
Thunderstorms*
Land heating quicker than oceans
Happens in summer
Air rising creates low pressure
Polar low
Happens in winter
Polar or arctic winds
Gain energy from relatively warm sea compared to relatively low air temp. Struggle to maintain energy over land
Orographic low
Where high pressure becomes low pressure on the other side of a mountain. Creates mountain wave and turbulence
Trough
Extension of low pressure
Poor weather, clouds, TS, RA, SHRA
At what height are met chart figures given?
2000’
Ridge
Extension of high pressure.
Similar to high pressure but moves through more quickly (6-18 hours)
Col
H
L L
H
Light winds
Variable weather each time one appears
Slow moving
ISA Standards
Pressure -
Temp -
Lapse rate -
Tropopause height and temp -
Sea level density
1013.2 hPa
15 degrees c
2deg/1000’
36,090’, -56.5c
1.225kg/m^3
Height of tropopause and what affects its height
36090 ISA
Equator - 55,000’. Warmer air, less dense, more volume
UK - 35,000’
Poles - 25,000’
Significance of the tropopause
Clouds/weather rarely occur above tropopause
High winds (jetstream) just below tropopause
Clear air turbulence occurs here
Contrails
Engines are more efficient (coldest temperature)
Trigger actions for clouds forming
Convection (ground heating)
Orographic uplift (air forced up by high cloud??:??)
Convergence (air pushed up, e.g. during trough)
Mass ascent (fronts)
Turbulence (less common)
Difference between stratus and cumulus
Stratus - Flat
Cumulus - Bubbly
What temperature range does most icing occur?
0 - -20c
Clear ice
Forms in cloud
Just above 0c (medium level)
Large droplets
Freeze slowly, allowing air to escape, therefore dense
Runs back
Rime ice
Forms in cloud
Higher than clear ice
Small drops
Freezes quickly
Trapped air, less dense
White
Which kinds of ice would you experience in cloud
Clear and rime ice
Hoar frost
Forms in clear air
Freezes quickly
Deposition
Freezing rain causes what intensity of icing and happens where?
Severe icing
Happens just ahead of warm fronts
Severity of icing
Trace, pereceptible
Light, 0.5cm, 15-60mins
Moderate, 0.5cm, 15 mins
Severe, 0.5cm, 5 mins
METARS
Meteorological aerodrome report. Issued every 30 mins. Observations at XX:20 and XX:50
Meaning of SPEC B or SPEC M
SPEC B - METAR has improved
SPEC M - METAR has deteriorated
Often only stated if new METAR not at regular intervals
When will a TAF be ammended?
Wind changes by 30 degrees or 10kts
Change of colour state
