Meteorology Flashcards
Typical tropopause heights and temperatures
53,000ft (16km) at equator, -75C.
36,000ft (11km) at mid-lat, -56C.
26,000ft (8km) at poles, -45C.
Risk of ground collision when heading to high or low pressure
Altimeter will over-read if heading into low pressure risking ground collision.
Think about what would happen if you adjusted to the correct pressure setting (turn down to the lower pressure setting, indicated altitude would fall).
Density altitude
- description
- calc
The altitude at which observed air density would be found in an ISA standard atmosphere.
Or, pressure altitude adjusted for ISA temperature difference (@120ft per C)
Depression weather
- Cloud, prec, vis, temp, wind
Cloud - extensive (including vertically)
Prec. - Intermittent or continuous, light to heavy
Visibility - Good unless in rain
Temp. - Brings colder air in summer, warmer in winter
Winds - Strong
Anticyclone weather (summer)
- Cloud, prec, vis, temp, wind
Cloud - None
Prec. - None
Visibility - Moderate (haze)
Temp - Variable
Wind - Light
Anticyclone weather (winter)
- Cloud, prec, vis, temp, wind
Cloud - Low stratus
Prec. - Drizzle
Visibility - Poor (mist/fog likely)
Temp - Warm
Wind - Light
Lifecycle of Atlantic depression
4-7 days
Turbulence that pilots should report
High level (> FL150) clear air turbulence (i.e. not associated with cumuliform cloud or thunderstorms).
Report time, location, level, intensity and aircraft type
Consequence of temperature error on decision height/altitudes
Need to be adjusted when temperature more than 15C below ISA
[increase by 0.4% per deg C]
Jet streams
- position relative to tropopause
- speed
- dimensions
Strongest upper thermal winds JUST BELOW tropopause, >60kts (up to 300kts).
Assumed 2000 miles long, 200 miles wide, 2 miles deep. [ratio 1000:100:1]
Jet stream altitudes
Equatorial: 50,000ft, 150hPa
Sub-tropical: 40,000ft, 200hPa
Polar front: 30,000ft, 200hPa
Arctic: 20,000ft, 400hPa
Bergeron Theory
(Norwegian or Ice Crystal theory)
Bergeron theory is that precipitation is caused by some water droplets turning to ice, growing in size through sublimation with water vapour and colliding with supercooled droplets. These droplets then become heavy and fall as rainfall or snow depending on temp.
Related to the partial pressure of water vapour over ice/water.
Coalescence Theory
Assumes a variety of droplet sizes, with larger ones falling faster and uniting with smaller ones, eventually overweight drops fall as DRIZZLE or LIGHT RAIN.
Avoidance distance for thunderstorms on radar (by flight level)
0 - FL250: 10NM
FL250-300: 15NM
FL300+: 20NM
Vertical: 5000ft
[Visual avoidance - 10NM]
Thunderstorm risks
Turbulence
Hail (up to 45000ft)
Icing (airframe -45 to 0C, carb -10 to 30C)
Lightening (within 5000ft of freezing level, temp -10 to +10C)
Static (affects radio equipment)
Pressure variations
Microbursts
Water ingestion (in jet engine)
Tornadoes
Microburst
- downdraft speed
- windspeed & windshear
- size
- time
Down currents in cloud and also outwards due to ground impact.
c. 3000fpm downwards (up to 6000fpm) and 50kt horizontal (in 2 directions, so up to 100kt windshear)
Only 4km horizontal length and last < 5 mins.
Tornado (funnel cloud)
- description
- size
- time
Connected to thunderstorms, caused by opposing vertical airflow movements. Diameter generally less than 150m but can be up to 1.6km. Called funnel clouds if they don’t reach the ground (can be embedded within cloud).
Last a few mins up to 30 mins.
Freezing fog
With temperatures below 0C air won’t sublime due to lack of freezing nuclei, but will freeze on contact with an object.
Can also happen when fog forms over 0C and air then cools below 0C.
Jet engine icing
Jet engines often have some degree of convergence (high air velocity, temp and pressure falls) which can cause intake icing. Operating manual will describe the risk and RPM, airspeed (etc.) to avoid (likely to be high RPM and low airspeed).
Polar Front Depressions
- creation
- pressure aloft
Main cause of UK bad weather, depressions formed in families along the polar front (mPc, mTw). Warm Tropical air pokes into cold air creating the warm sector. The warm air surrounded by cold will rise and make this a depression.
Move parallel to the warm sector isobars.
Low pressure at high altitude as well as at the ground (unlike warm depressions).
Warm front
Low slope (1:150) rising over cold air, Ci and stratiform cloud types behind the front.
Total distance of 400/600nm, rain up to 200/300nm under the lower Ns clouds.
Moves at right angles to itself, at 2/3 of the geostrophic interval at the front.
Cold front (inc. cloud types
Steep slope (1:80) forces warm sector air up quickly, forming Cu, Cb cloud (& Ns) ahead of it - heavy showers. Low pressure at the front itself (so passing of the front sees pressure fall then rise within the cold air following).
Passing of warm front
- pressure
- wind direction
- cloud
- precipitation
- temp
- visibility
Pressure falls as the centre of the low is approaching you (travelling Eastwards to your north).
Sharp veer from S to SW.
Cloud increases as it approaches (Ci, Cs, As) then Ns and drizzle as it gets closer. Continuous rain as it passes.
Frontal fog as it passes.
Temp & dew point rise as it approaches.
Reducing visibility.
Passing of cold front
- pressure
- wind direction
- cloud
- precipitation
- temp
- visibility
Pressure low point around the front (closest to centre of the low) then increases after passing.
Sharp veer from SW to NW.
Cu/Cb/Ns cloud, heavy rain or snow showers, thunder/hail possible (air forced upwards steeply by cold front).
Temp & dew point fall.
Visibility good except in showers.
Conditions in cold air behind cold front
Cumulus clouds (cold air aloft gives steep pressure gradient therefore instability).
Showers
Good visibility
Tropical Revolving Storms (TRS)
- Description
- windspeed
- Size
- Time
aka hurricanes. Thermal depressions over warm tropical oceans with sustained wind speeds over 33kt. Designated tropical cyclone if sustained wind speed over 63kt [NO LONGER A TRS!, max TRS windspeed 63kt!]
270 NM (500km) diameter
Heavy rainfall
Tornados may be faster, but only last for minutes, TRS last for a couple of weeks.
METAR
Meteorological Aerodrome Report
Half hourly report of current weather conditions at an aerodrome
METAR RVR
- codes
“R30/P1500”: RVR > 1500m (i.e. plus)
“R30/M0050”: RVR < 50m (i.e. minus)
If RVR increases by 100m in last 10 mins add “U” at end, if decreases add “D”, if no trend add “N”
Can have two figures separated by “V” if significant variation in last 10 mins.
METAR weather codes
“+”
“-“
“ “
“VC”
“=”
”+”: Heavy
“-“: Light
“ “: Moderate
“VC”: In the vicinity (within 8km)
“=”: Termination symbol
METAR weather codes
“MI”
“BC”
“BL”
“SH”
“TS”
“FZ”
“PR”
“DR”
“MI”: Shallow (<2m above ground)
“BC”: Patches
“BL”: Blowing
“SH”: Showers
“TS”: Thunderstorms
“FZ”: Freezing (supercooled)
“PR”: Partial (covering of aerodrome)
“DR”: Drifting
METAR precipitation codes
“DZ”
“RA”
“SN”
“IC”
“PL”
“GR”
“GS”
“UP”
“PY”
“DZ”: Drizzle
“RA”: Rain
“SN”: Snow
“IC”: Ice Crystals
“PL”: Ice pellets
“GR”: Hail
“GS”: Small hail (<5mm)
“UP”: Unknown precipitation
“PY”: Spray
METAR obscuration codes
“BR”
“FG”
“FU”
“VA”
“DU”
“SA”
“HZ”
“BR”: Mist (vis 1000 to 5000m)
“FG”: Fog (vis <1000m)
“FU”: Smoke
“VA”: Volcanic Ash
“DU”: Dust
“SA”: Sand
“HZ”: Haze
What is obscuration?
Something blocking vision that is NOT precipitation (e.g. haze, mist, sand)
METAR other codes
“SQ”
“FC”
“SS”
“SQ”: Squall
“FC”: Funnel cloud (tornado)
“SS”: Sandstorm/duststorm
When is TS included in METAR?
Thunder heard in last 10 minutes
Cloud types specified in METAR
Cb: Cumulonimbus
TCu: Towering Cumulus
CAVOK requirements
- Visibility >10km
- Cloud base >MAX(5000ft, MSA)
- No Cb or TCu
- No significant weather in vicinity (e.g. RERA)
METAR “RE”
“RE”: Recent - in the last hour
e.g. “RETS” thunderstorm in last hour
METAR “WS”
“WS”: Windshear
Could specify a runway number or “ALL RWY”
METAR
“TREND”
“BECMG”
“TEMPO”
“NOSIG”
“TREND”: Valid for 2 hours FROM TIME OF OBSERVATION
“BECMG”: Changes becoming permanent
“TEMPO”: Less than one hour and less than half the time period
“NOSIG”: No changes expected in next 2 hours
METAR
“SNOCLO”
Closed due to contamination
METAR components in order (9)
EGKK (Location)
121200Z (DDTTTT) [Deduct 1hr for Zulu!]
02015G30KT (Wind)
9999 (Visibility)
R26/0400 (RVR)
DZ (Weather)
FEW020 (Cloud)
18/10 (Temp/DP)
Q1019 (QNH)
TAF
“NSC”
No significant cloud
Means no cloud below 5000ft or sector altitude, no Cb or TCu, but CAVOK not appropriate.
TAF
“TX”
“TN”
“AMD”
“TX”: Maximum temperature
“TN”: Minimum temperature
“AMD”: Amendment
AIREP
Report from pilot on weather (PIREP in USA). Can be handed in at end of flight as written report.
AIREP SPECIAL (or ARS) reported immediately in case of:
Mod/Sev turb or icing
Sev MTW
TS (OBSC, EMBD, WDSPR or SQL)
Heavy dust/sand storm
Volcanic ash
Sections of a special AIRREP
1) Aircraft identification, position, time, level
2) n/a
3) Meteorological info
Where does doppler radar measure turbulence?
Thunderstorms, picks up precipitation.
