MET 1 EXAM DECK Flashcards
Define Met in terms of Flight operations
A consideration of all available wx information to be able to plan & execute safe & economical flight ops.
Composition of dry air
78% Nitrogen
21% Oxy
1% Trace gasses
What are the components of the atmosphere that are most important to wx & climate
- Water vapour (main driver for wx)
- Aerosols (provide ice & condenstation nuclei)
- CO2 (absorbs terrestrial radiation & warms atmosphere)
- Ozone (Absorbs UV radiation from sun)
Describe the characteristics of the troposphere
- it is always in motion
- It holds 75% of the mass of the atmosphere in mid latitudes & 50% is found below 5km.
- temp decreases with increase in altitude.
- SFC to 36,090ft: Troposphere.
- Capped by Tropopause (isothermal layer) up to 20km
- Stratosphere above
Describe the temp characteristics through the atmosphere
- ISA lapse rate of 1.98 C/1000ft up to tropopause (11km)
- Isothermal from tropopause at -56.5 C up to 20km
ISA figures (MSL)
15deg C temp
1.225kg/m3 Density
1.98 C/1000ft lapse rate
1013.25hPa pressure
AT MEAN SEA LEVEL
How does the height of the troposphere vary?
Average height is 36,090ft in mid-latitudes.
Approx 56,000ft at equator & 28,000ft at the poles.
Changes due to direct warming at the equator & angle of the sun.
Define the two types of radiaiton
General RoT?
Short wave: incoming solar radiation from the sun
Long wave: outgoing terrestrial radiation from earth.
Incoming net short wave radiation must meet net outgoing long wave radiation.
What are the 4 main heat transfer processes in the atmosphere?
Additional one?
- Convection (tsfr through vertical movement of warm air)
- Conduction (tsfr by touch)
- Advection (tsfr by horizontal movement. e.g. wind)
- Radiation
Latent heat
Why do seasons occur?
Due to the tilt of the earth as it rotates around the sun.
Define Albedo
Ocean high or low?
The portion of incident light or radiation that is reflected by the earths SFC. (resistance to being warmed)
E.g; Snow = high albedo, forest = low albedo.
Ocean is high when angle of sun is high, low when sun is low.
Define specific heat
The qty of heat energy required to raise the temp of unit mass of a substance by 1deg C
Define an inversion
An increase in temperature as altitude increases.
List the four types of inversions
- Radiation
- Turbulence
- Subsidence
- Frontal
How is a radiation inversion created?
Occurs on clear skies with light winds. Radiation fog/mist common as a result.
- LW radiation released from earth to atmosphere
- SFC cools & air in contact with the ground loses heat through conduction & low level mixing. (100-300ft layer AGL)
- Temp above layer unaffected & is therefore warmer than the air below.
Draw a graph depicting radiation inversion
How is a turbulence inversion created?
- Turbulent mixing below friction layer due wind blowing over SFC obstacles
- Air rises & expands, cools adiabatically & vice versa.
- Steeper lapse rate created (~3deg/1000ft)
- Air above friction layer unaffected, remains warmer than induced cooling below. (due to being at original normal lapse rate)
What determines the depth of a turbulence inversion
Strength of the wind & SFC roughness
When would you expect a turb inversion, altitudes?
Common with winds >10kts, inversion usually between 1000-5000ft (most common 2-3000ft)
How does a subsidence inversion form?
- Developing SFC high px system
- Sinking of air from aloft
- SFC pressure rises, compression = warming adiabatically.
- Inversion created mid troposphere (approx 3-8000ft)
How does a frontal inversion form
At frontal boundary when warm air is forced to rise over cool air.
Alt of inversion depends on where you are relative to the front. (further away = higher & vice versa
Draw a graph depicting Frontal inversion
Draw a graph depicting Turbulence inversion
Draw a graph depicting Subsidence inversion
List the 6 effects of inversions on flight
- Cloud tops; inversion acts as ‘cap’, tops spread out below
- Perf effects: decreased a/c performance flying through inversion (warm air = reduced thrust etc)
- Vis: lid for haze/smoke
- W/S & turb: decoupling b/t winds below inversion & laminar/strong winds aloft
- Refraction: comms disruptions
- Dew Point: Inversions cap moisture, water vapour increases underneath = higher DP.
Define Pressure
Total weight of the column of air above the point from which px is being measured.
Pressure lapse rate?
30ft/1hPa
QNH
A/D level px corrected to MSL using ISA lapse rate.
Altimeter reads ALTITUDE above MSL.
(SFC-13,000ft)
QFE
A/D level px.
Altimeter reads HEIGHT above A/D.
(Set for Aeros/Displays)
QNE
1013.25hPa set
Altimeter will read PRESSURE ALT or FLIGHT LEVEL of a/c.
(Set above 13,000FT)
Exceptions to F150 as transition level?
When SFC pressures <980hPa.
IMC within 20nm of Mt Cook .
RoT wrt change in px over long distances
High to low (QNH`), watch out below
How to calc PA?
PA = AD alt +/- (AD px -1013) x30ft
How to calc DA?
DA= PA +/- (ISA temp dev) at 1C/120ft
Effects of temp on Px
How does this affect PA?
Increase in temp (>ISA) = px decrease (due expansion of air), therefore PA will be higher & vice versa.
What is DA affected by?
Temperature, PA and moisture content of the air.
What does “high DA” refer to?
Where would you expect a high DA?
The body of air will have a density normally found at a higher altitude.
Locations that are hot & high alt. (low px)
How does high DA impact a/c performance?
Perf is reduced/degraded;
- T/O ground roll longer
- LDG speed higher (longer LDG dist rqd)
- ROC decreased
- Service ceiling reduced
Define a gust
Increase of at least 10kts above mean wind speed
Define a squall
Increase of at least 16kts above mean wind speed, at least 22kts , lasting for longer than 1 min
Define a gale
10min mean wind speed between 34-47kts
Veering vs. backing
Veering: Clockwise
Backing: anticlockwise
How is wind measured
10min mean average, 10m above the ground
True vs. mag
Written: true
Spoken: mag
7 methods to estimate SFC wind
- Windsock
- Cloud shadows
- A/C drift
- Water ripples
- Cows (>25kts)
- Beaufort scale
- Smoke drift
-Crop/tree movement
Define coriolis force
An inertial force that acts on objects that are in motion relative to a rotating frame of reference
3 properties of CF?
- Strength is proportional to wind speed
- Proportional to the sine of the latitude (nil at equator, max at the poles)
- Always acts at right angles and to the LEFT in SH.
What are the 3 forces acting on wind?
- Pressure gradient force (always from H to L, proportional to isobaric slope)
- Coriolis force
- Friction (acts against motion of wind)
Define the geostrophic wind balance
The wind that would result from the exact balance of PGF and CF when isobars are STRAIGHT.
(friction not considered)
Results in wind flowing PARALLEL to isobars
Draw the geostrophic wind balance
Describe how forces interact for equal isobar spacing (L and H)
H: CF > PGF
L: PGF > CF
“Winds fly around a High and go slow around a Low” (for equally spaced isobars)
How does friction affect the GWB?
Friction opposes direction of motion, slows wind down, PGF stays the same, CF ‘tilts’ to counter - resultant wind crosses isobars direct to the L
Buys Ballot’s law
If you stand with your back to the wind (SH), low is on your right.
How to estimate wind using 2000ft wind?
2/3 strength of 2000ft wind, gusting to full strength.
veer 30deg from 2k wind.
How does wind vary with height?
SFC wind will BACK with altitude (due removal of friction)
Describe GWB around anticyclonically curbed isobars
- PGF first to chg direction around corner to remain H > L
- Wind speed increases, as a result, so does CF
- CF now stronger than PGF. Excess CF = centripetal acceleration rqd to “bend” around isobars
Describe GWB around cyclonically curbed isobars
- PGF rotates slightly in clockwise direction (acts INWARDS towards L)
- PGF vector therefore moves backwards AGAINST wind vector & slows wind down.
- CF therefore decreases, PGF is greater than CF. PGF provides acceleration to curve around the isobar
How does wind vary with the diurnal cycle
- Night: lower atmosphere is more stable = decoupling from upper winds & therefore wind speed reduces
- Day: SFC winds are influenced more by upper winds = increase in wind speeds (max in arvo).
Difference b/t streamline analysis and MSL charts
Streamlines show wind DIRECTION only.
(Used in tropics due lack of CF & px systems)
Define Isobars
Lines that connect areas pf EQUAL px
Define an anticyclone
Region of relatively high px shown by one of more enclosed isobar. Surrounding pxs are lower than central px.
Associated with good wx
Define a ridge
extension of isobars away from central High, associated with good flying condxns.
Never marked on MSL chart
Define depressions
Region of relatively low px shown by one of more enclosed & concentric isobar. Surrounding pxs are higher than central px.
Associated with strong winds & poor wx
Define a trough
extension of isobars away from central Low. Px of trough line is LOWER than px either side.
Associated with poor flying condxns. Sharp chg in wind direction.
All fronts are troughs
Define a Col
An area of opposing highs and lows.
Moisture converging along axis can = TS & FG
Define a front
Fronts mark the boundary between two airmasses with different temp & moisture characteristics
Define a cyclone
Named, TC in centre, A deep depression, isobars very close together
What is a katabatic?
3 requirements?
A Down slope wind
1. Clear night
2. Sloping ground
3. Slack px gradient
How does a katabatic form?
OH Katabatic?
- High terrain (mtns/ranges) & loss of long wave radiation at night. Air in ctct with SFC cools through conduction & contracts. It is then heavier than above free air, and slides down slopes under the weight of gravity.
OH: 030T/5-10kts
Requirements for sea breeze to develop?
- Coastal situation (beach/lake)
- Fine wx (esp summertime)
- Slack px gradient
- Period mid morning to late arvo for onset
How does a sea breeze develop?
- Land heats up faster than water, air at SFC heats up through conduction, expands & lifts to create H px aloft.
- Px gradient aloft created with upper L out to sea. (~1000ft)
- Further heating over land & rising of air = low Px immediately above SFC.
- Remaining circulation kicks in & seabreeze created
Typical sea breeze in OH?
250T/12-15kts
What is terrain chanelling?
Occurs when wind is forced through a constriction caused by adjacent high ground. (venturi effect)
What increases the effect of terrain chanelling
Stronger px gradient = stronger wind
Steepness & proximity of high ground (closer = stronger)
Stable atmosphere (air doesn’t want to rise)
3 most common/important areas for terrain channeling?
- Manawatu gorge (W or E)
- Cook strait (N or S)
- Puysegur pt (NW or SE)
Sumblimation?
Frozen > liquid > vapour
Heat energy TAKEN from environment & stored as latent heat
Deposition?
Vapour > Liquid > frozen
Latent heat RELEASED (warms atmosphere)
What is the general RoT with regards to ability for air to hold water vapour?
Hot air can hold more water vapour, cold air can hold less.
Factors that increase rate of evaporation?
- Higher H2O temp
- Higher air temp
- The drier the air
- Increased wind speed
Define Dew point
The temp to which air must be cooled for it to become saturated at a constant px.
(when cooled past this condensation will occur)
Temp = DP: saturation will occur
If H2O is added to the atmosphere what will happen to the DP?
DP temp will increase
Define relative humidity
What causes it to change?
The ratio of the amount of water vapour present in the air, to the amount of vapour rqd for saturation to occur at the same temp (%)
A chg in water vapour content of the parcel of air or air temp
Define Stable
Air displaced vertically is colder than the environment and sinks back to original level once lifting force is removed
Define Unstable
Air displaced vertically is warmer than the environment and will continue to rise once lifting force is removed
Define conditionally unstable
Air that may become unstable when displaced vertically. Dependent on the moisture level of the air.
SALR vs ELR vs DALR
SALR: Saturated adiabatic lapse rate (100% RH) = 1.5deg/1000ft
ELR: Environmental Lapse Rate; the ACTUAL lapse rate at the given time (ISA = 1.98 deg/1000ft)
DALR: Dry adiabatic lapse rate (1-99% RH) = 3 deg/1000ft
Why are DALR & SALR different?
Rate of cooling during continued lifting is offset by latent heat release during condensation. Added heat doesn’t stop cooling but slows it down
Describe adiabatic process to form cloud
- Parcel of air triggered & begins to rise
- lifting means px of environment decreases
- expansion & cooling of parcel
- ^ continues until temp of parcel reaches DP/saturation point
- Water vapour condenses & cloud will form
ELR between DALR & SALR?
ISA ELR?
Conditionally unstable. Depends on whether or not parcel is dry or saturated as to if it becomes unstable or not
(saturated = unstable/dry = stable)
With ISA ELR being 1.98deg/1000ft, it is always conditional
ELR greater (hotter) than SALR & DALR
Parcel is always stable
ELR less than (colder) than SALR & DALR
Parcel is always unstable & will rise until situation becomes stable again.
4 triggers for ascent of a parcel of air?
(and therefore creation of cloud)
- Convection (air in ctct with warm SFC heats & rises)
- Orographic lifting
- Windespread ascent (L or frontal lifting)
- Turbulence
Cold sthly maritime flow?
Dry & cold air from poles moves over warm water & heats from below.
= Unstable cdxns & convection
= Cu, Cb, Tcu & showers
Warm Nthly maritime flow?
Moist warm air from tropics moves over cooler water & cools from below
= Stable condtions
= St cloud develops with DZ & RA.
Sea fog can also form
What is required for turb to exist
Windshear
List the types of turb
- Mechanical (due buildings/terrain)
- Convective (due thermal rising of air & mixing)
- Wake
- CAT (jet streams)e
Define windshear
What are severe shears caused by?
A sudden chg in wind speed and/or direction over short distance (vertical or horizontal)
Severe shears are most often associated with strong temp or density gradients
Causes of low level wind shear
- SFC friction
- Inversions (causes decoupling)
- TS (Up & down drafts)
- Frontal activity
Moderate vs. Sev turb icons?
Oktas?
1-2: Few
3-4: Scattered
5-7: Broken
8: Overcast
High level cloud types, codes & altitude
> 20,000ft to tropopause
Cirrus (Ci), Cirrostratus (Cs), Cirrocumulus (Cc)
Mid level cloud types, codes & altitude
6500-20,000ft
Altostratus (As), Altocumulus (Ac), Nimbostratus (Ns) - can also extend low level.
Low level cloud types, codes & altitude
<6500ft
Stratus (St)
Stratocumulus (Sc)
Cumulus (Cu)
Cumulonimbus (Cb)
List the factors that change cloud shape (5)
- Temp of environment
- Stability
- Windshear
- Shape & roughness of underlying terrain
- Moisture content in the air.
3x factors that can dissipate cloud
- Sinking of air
- Direct warming
- Mixing with clear air
Additional cloud types (3)
Tcu (towering cumulus)
Rotor clouds
AC lenticularis
What are 6 types of precip & their codes
- Virga
- Rain (RA/SHRA)
- Drizzle (DZ)
- Snow (SN)
- Sleet (RASN)
- Hail (GR/GS)
Precip rates?
Light: trace - 2.5mm/hr
Moderate: 2.5-10mm/hr
Heavy: >10mm/hr
Describe the Bergeron Process
- Air is saturated wrt liquid H2O molecules. H2O molecules are at equilibrium with SCWD
- Ice crystal is introduced. Air is now super saturated wrt the ice.
- H2O molecules deposit onto ice crystal & it grows.
- Air becomes unsaturated wrt SCWD & they start to evaporate
- Results in Saturated air wrt Ice & SCWD completely evaporated.
Describe how the Bergeron process results in rainfall.
Ideal temp required?
- Growth: Evaporating SCWD deposit onto ice crystals.
- Aggregation: ice crystals collide & grow in size
- Rain: ice crystals become too heavy & fall through FZL, melting into rain
MOST COMMON PROCESS IN NZ DUE AVE HGT OF FZL
Air temp around -15deg C
Describe the coalescence process.
Requirement?
- Collision: Rain droplet growth through smaller droplets colliding with larger droplets.
- Sweeping: area of lower px behind large droplets ‘pulls’ small droplets in.
- Rain: Droplet becomes too heavy & will fall to SFC.
RQRS TEMPS >0deg C (more common in tropics)
Three factors affecting fall rate of rain
- Gravity
- Droplet size & mass
- Strength of up & downdrafts in the cloud.
What does the Bergeron process rely on?
Ice crystals growing at the expense of evaporating SCWDs
Effect of precip on visibility
Light: little reduction
Mod: 10km down to 3000m
Heavy: <3000m
Effect of DZ & SN on visibility
Light: >8000m
Mod: 8000m down to 500m
Heavy: <500m
Effect of FG, BR & HZ/FU on visibility
Fog: <1000m
Mist: 1000-5000m
Haze/smoke: <5000m (particulates OTHER than water vapour)
What is slant range?
How far a pilot can see through a layer of fog/mist
Why does illumination from the sun/moon have NO effect on vis?
Vis is NOT a function of illumination, but rather a function of the TRANSPARENCY of the air.
Causal factors of poor vis? (4)
Droplet numbers
Droplet size distribution
Composition (water/ice)
Illumination (brightness & direction)
Types of precip/matter that will cause poor vis? (5)
- FG/BR
- Precip
- FU & HZ
- Dust & Sand
- BLSN
What is radiation fog caused by.
The earth cooling at night due loss of terrestrial radiation to space
How is radiation fog dispersed
- Warming of air from below
- Increased wind (results in mixing with warmer air)
- Dry air
5x conditions required to create radiation fog
- Clear skies
- Over land masses
- Evening to early AM
- High RH near SFC
- Light wind 2-7kts
Conditions for advection fog to be created/dispersed?
In what type of flow would you expect advection fog?
- clear or cloudy skies
- over land or sea
- At any time of day
- High RH near SFC
- Any wind 5-25kts
Dispersal requires synoptic scale chg in wind/temp.
Essentially warm air moving over cold see (Nthly maritime flow)
How is vis affected by cloud?
High
Middle
Low
Cu
High: >1000m
Middle: 20-1000m
Low: <30m
Cu: <20m
Change groups:
FM
BCMG
PROB 30/40
FM: complete chg from base line of the TAF
BCMG: Permanent chg of a component of the base line of the TAF expected gradually through period of time specified.
PROB 30/40: probability of 30 or 40% of a certain wx cdxn, usually attached to TEMPO.
What is a METAR
A/D routine Met report
Manually issued on the hour during ATC hours (OH, WP, Milford Sound)
What is a SPECI
Special Met A/D report
Issued off the top of the hour when cdxns deteriorate below/improve past;
<1500ft cloud base
<8000m vis
Sig change in wind direction
What are the 5 types of fog?
- Radiation
- Advection
- Steam
- Frontal
- Upslope
AAW provides?
Wind (True) speed & direction up to 10,000ft AMSL.
Temps also from 5000ft up
What does a GRAFOR provide?
Issued & Valid?
Worst conditions expected within section, up to 10,000ft AMSL.
00Z, 06Z, 12Z, 18Z.
Valid for +/-3hrs of fixed validity time.
NSC?
Nil Sig Cloud
TAFs/METARs: Nil CB/TCU observed at any height, nil cloud below min sector altitude
GRAFORs: (less than 3 oktas and/or bases higher than 10,000ft AMSL)
ISOL
OCNL
FRQ
ISOL: <50% max spatial coverage
OCNL: 50-75%
FRQ: >75%
What are SIGMETs issued for? (7)
SEVERE
- TS
- Icing
- Mountain waves
- Turb
- TC
- Heavy Sand/dust storms
- Volcanic ash/ejecta
SIGMET Validity?
Exception?
4 hrs
TC & Volcanic ash 6hrs
STNR
WKN
INSTF
NC
STNR: Stationary
WKN: Weakening
INSTF: Intensifying
NC: No chg in intensity
TAF?
Validity?
Fcst wx conditions within an 8km radius of the A/D reference point
12hrs (domestic)
30hrs (international)
TAF Issue times?
Domestic: 2300/1100Z
International: 4hrs per day, approx 1hr prior to validity period
Trend?
Appended to METAR/AUTO/SPECIs
Trend takes precedence over TAF for 2hr validity period
METAR AUTO?
Issued every half hour by AWS.
Prevailing Vis?
9999?
Max vis covering at least half the horizon
9999 = >10km
CAVOK
Cloud & Vis OK
Vis >10km
Nil Cb/TCu at any alt
Nil other cloud below min sector altitude
TEMPO
Temp chg in cdxns of the base line of the TAF for no more than 1hr at a time in the indicated time frame.
Temp conditions ae less dominant than original forecast conditions
RE?
Recent, within the last 1hr
VCY?
in the vicinity
between 8 to 16km of A/D Reference point
AGL vs. AMSL
AGL: TAFs/METARs/METAR AUTO/ATIS/SPECI
AMSL: GRAFOR/SIGWX/SIGMET/ ROFOR/AAW
Define the “gradient wind”
A horizontal wind having the same direction as the GWB, but with a magnitude consistent with a balance of THREE forces (CF, PGF, Centripetal Force)
Centripetal force resulting from curvature of parcels trajectory around isobars
When would you expect W/S associated with frontal activity?
Fronts moving faster than 30kts across the ground, OR temp diff across the front is >5 deg
What are the 6 most important products for flight planning
- GRAFOR
- AAW
- SIGMETs
- GNZSIGWX
- TAFs
- METAR
(ROFOR)
Define transition layer
13,000ft-FL150
Provides sep from terrain and other aircraft
What wx are CBs associated with?
TS - thunder & lightening
Strong up & downdrafts
Microbursts
+SHRA/GS
Gust front
Sev Icing & turb
Poor vis
