AMET

Atmosphere

Troposphere

Most weather here. Tropopause = boundary in atmos where temp stops dec w/ alt
Poles = 25,000 (8km) @ -40°
Equator = 60,000 ft (18km) @ -70°

International Standard Atmos (ISA)

Enviro temp lapse rate (ELR) from 0 -> 36,000ft = 2°
ISA MSL temp = 15°, tropopause temp = -56°

Heat Transfer

• RADIATION – electromagnetic waves. Anything abv absolute 0 = radiate heat. Hotter = shorter wave length. Sun = hot -> short wave radiation (aka insolation). Earth = cool -> long wave radiation (aka terrestrial radiation). Heat transfer can’t occur vacuum -> sun heats earth surfaces
• CONDUCTION – transfer w/ contact. E.g. air contacts earth surface (bad conductor so only heated close)
• CONVECTION – transfer through movement of body (usually vert). Heated air = less dense -> warm air rises, cooling horizontally and falling. Diagram on parts of cycle:

Atmos Heat Transfer – only ½ of insolation is absorbed by surface. ½ lost by reflection from ground / cloud tops, scattering by dust / water vapor / smoke

Terrestrial rad = harder to penetrate atmos (longer wavelength = more readily absorbed by water vapor / co2 -> molecules radiate heat back = greenhouse)

Temp @ surface depends on:

• Reflectivity of surface
• Conductivity of surface
• Specific heat of surface (heat energy required to raise temp of object by 1°)
• Cloud Cover (lower temp during day, but insulate against loss night = flatter temp curves)

Diurnal Variation Temp

Sea = less 1°
Desert = 20° 24hr period

Peak high ~2-3pm (surface air continues to warm by conduction)
Peak low ~dawn (surface lost all heat through terrestrial rad)

• Inland areas = greater diurnal temp than sea (higher specific heat). Inland heat up / cool down more
• Wind = mix air, reduce diurnal variation, calm = bigger diurnal variation in air temp
• Cloud cover = reduce diurnal variation at particular place

Vertical Temp Distribution

Atmos mainly heated from terrestrial
Lapse rate of temp is 2° per 1000ft to Tropopause

NB – joined lines on weather map of same temp = isotherms
NB – joined lines of same surface pressure = isobars

Pressure

78% nitro, 20% oxy, 2% other

Mercury barometer – evacuated tube, open end in mercury. Air press down mercury = rise in tube (due weight air)
Aneroid barometer – flexible metal chamber, partially evacuated, fixed at one end. Other end is on dial (similar alt)

Pressure = force per unit area

Pressure Units

Inches of Mercury (Hg) -> engine manifold.
Millibar (Mb) = pressure 1/1000^th of a bar (approx. sea lvl pressure)
Hectopascal (HPA) = force 100newtons per square meter. We use HPA. Interchangeable with Mb

Standard atmos sea lvl pressure = 1013.25 HPA (29.92” Hg)

Vert pressure distribution – lower troposphere = -1 HPA every 30ft

Atmos Air Density

Density = mass of air occupying given volume.

Depends on:

• Pressure – directly related to density. Dec pressure -> dec density
• Temp – inversely related. Inc temp -> dec density
• Humidity – inversely related. Inc temp -> dec density (1 molecule of water vapor has less mass than average air molecule -> inc concentration water vapor lowers overall mass of air volume = lower density)

High density = great performance

Variations In Air Pressure

Pressure on earth surface varies due to:

• Movement pressure systems
• Changing intensity pressure systems
• Semi diurnal pressure variation – expansion / contraction of atmos as warm / cool. Greatest tropics (~5HPA)

Mean Sea Level Pressure

• QNE = standard mean sea level pressure in ISA
• QNH = actual mean sea level pressure
• QFE = station level pressure

Local QNH = actual sea level pressure for location.
Area QNH = Area QNH zone (AQZ). Forecast by BOM for 3hr periods. Area QNH may differ from local QNH at any point w/I area, but not more 5HPA, or to adjoining area by 5HPA (will subdivide if issue)

Altimeter Settings

• Airfield elevation on Main = approx. local QNH on sub
• QFE on sub = height above / blw reference pressure point on main (may be aerodrome lvl)
• QFE can be obtained by setting 0 on main
• 1013 on sub = pressure height on main

NB – if station is not sea level = 1HPA per 30ft correction used (below 5,000ft, pressure reduces more slowly higher). Correction assumes air is dry, conforms to ISA temp characteristics.

Can use local QNH if w/I 100NM of aerodrome when blw 10,000ft (CHECK THIS, I THOUGHT IT WAS 50)

Pressure Patterns

Isobar spacing = usually 2 / 4 HPA intervals

Alt flying towards LOW = OVER READ (falling pressure = climbing)

Pressure Gradient

Change in pressure w/ horoz distance

Measured from high to low pressure @ right angles to isobars. Close spacing = strong gradient / winds.

Atmospheric Stability

NB: water vapor held in saturated air = invisible always

Latent heat – heat which must be added to substance to change it into higher state (liquid to gas etc). Addition of latent heat results in change of state only (no change temp). LH is released by substance when changing to lower state. Exchange of latent heat occurs in all changes of state.

Humidity – amount vapor contained in air sample (measured psychrometer / wet dry bulb thermo / hygrometer)

Relative Humidity

Ratio of amount of water present in air sample compared to max amount that could be contained at that temp + pressure. It is percentage degree of saturation
Saturation (relative humid = 100%) = air cannot hold extra vapor w/o condensation

Temp + pressure of sample of air influence amount of water vapor able to hold.
Inc temp = inc ability of air sample to hold water vapour (thus, relative humidity is decreased w/ inc temp)

Dew Point – temp that sample of air = reach saturation (relative humidity 100%). Further drop temp = condensation
Dew point depends on moisture content of air sample, reduces by ~.6° per 1000ft AGL

Lapse Rates

As parcel air rises, atmos surrounding reduces = volume increases and temp decreases. I.e. if sample of air rises -> forced to cool due expansion (heat energy is spread out).

Adiabatic = change in temp due change in pressure, w/o change in total heat energy for air sample

Lapse Rate = rate at which air sample cools as it rises:

• Dry (unsaturated) – 3° / 1000ft (DRY ADIABATIC LAPSE RATE – DALR). If cool dew point -> saturated = condensation occurs. As it condenses to liquid, latent heat is released = cools more slowly. Leads into:
• Saturated – 1.5° / 1000ft (SATURATED ADIABATIC LAPSE RATE – SALR)

Dew point lapse rate = decrease in dew point temp as alt increases (.6° per 1000ft)

Stability

Stable atmos = air parcel temp b/c less than environment -> if lift force is removed -> returns to original level
Unstable atmos = air parcel temp remains higher than enviro -> keeps rising on own after lift force removed

Atmos stability depends on relative lapse rates of enviro and air parcel moving vertically.

ISA temp decreases by 2° per 1000ft, but real life may differ from this. Actual ELR = obtained through measurements

When a parcel of air forced vertically = will cool at DALR unless becomes saturated (dew point), then cool at SALR
Enviro itself will cool according to ELR

• STABILITY = ELR less than SALR
• INSTABILITY = ELR greater than DALR
• CONDITIONAL STABILITY = ELR less than DALR, but greater than SALR
• While parcel remains dry + cools at DALR, conditions = stable
• Dew point -> parcel cool at slower SALR, if sufficient lifting occurs, b/c warmer than enviro = instable
• NB: conditional stability aka conditional instability

Calculating Cloud Base Height

Need surface lvl temp and surface dew point.

Using dew point lapse rate (.6° per 1000ft), cloud base = (surface OAT – surface dew point) ÷ 2.4

If given dew point is from cloud base, diff b/w surface temp and dew point is divided by 3 (DALR) (thousands ft AGL)

Inversions

Warmer air above colder air

• Surface Inversion – air close to earth cooled at night. Greatest before dawn (surface temp lowest)

• Turbulence Inversion – mod winds at low lvl -> adiabatic expansion / cooling in lower layers due mixing. If lower layers b/c cooler = inversion

• Frontal Inversion – boundary 2 masses of diff temps may form inversion as warm air slides up over cool air

• Subsidence Inversion – column of air subsides -> the top of column undergoes greater compression + heating than bottom. Top b/c warmer, forcing inversion

Inversions = stable conditions. Warm air stops rising currents. Smoke / dust trapped underneath, bumpy

Fohn Wind

Hot / dry breeze blowing down lee slope of mountain.

Cloud base on lee slope = higher than windward due precipitation on windward + change in dew point. Lee = surface temps higher as air warms at DALR from higher cloud base through greater depth than it cooled on windward side.

Wind

Wind Velocity = vector quantity (vector is magnitude (kts) and direction). Measured 10mt over open lvl terrain, average measurement over 10 min.

Gust = sudden increase wind speed short time, then dying away
Squall = sudden increase wind speed by 16kts / more, lasting 1 min, reaching 22kts

Veer = clockwise wind direction change
Back = anticlockwise change

Forces Influencing Wind

• Pressure Gradient Force – Air flow from high to low, across isobars. Strength = depends on spacing of isobars, measured perpendicular to isobars
• Coriolis Force – Moving air deflected to left in south hemi due earth rotation. 0 at equator, max at poles. Strength also depends on wind speed (stronger wind = stronger coriollis deflection)

Global Circulation

Overall patter of circulation result of distribution of pressure systems (formed by uneven heating earth surface)

EQUATOR – Mass air warmed at equator, rises through convection = lots low pressure (equatorial trough / Inter-tropical Convergence Zone (ITCZ) / doldrums). Air cools and moves horizontally to the poles creating sub tropical regions (tropical ridge) from subsiding air.

POLES – cold dense air results in region of high pressure = polar high. Moves horizontally at surface -> converges w/ air from subtrop ridge and forced up = sub polar low.

Movement near surface from HP belts to LP belts = most of major air streams

Seasonal Winds

Tilt of earth axis = seasonal winds. Equatorial trough moves around:

• Summer = moves south near Nth Aus (thus NW airstream. Rain. Called NW monsoon -> brings warm moist air from ocean as warm currents rise from heated land surface). Summer in Nth hemi = equatorial trough moves further Nth due larger landmass in Nth and so high temps extend further poleward
• Winter = Nth Aus prevailing winds = SE due influence of SE trades. Dry conditions (bar Est coast = moisture)

Trade Winds

SE trade winds = subtropical ridge to equatorial trough. Large scale subsidence over subtropical ridge = widespread inversion extending towards equatorial trough. This trade wind limits vertical development cloud in SE trades

Roaring 40’s = prevail ~40° S as air from sub-tropical ridge down towards sub polar low. Direction NW in Sothern hemisphere due Coriolis deflection

Local Wind

Wind direction depends on relative strength of gradient force and Coriolis force

Gradient Wind – flows parallel to curved isobars when Coriolis force matches gradient force
Geostrophic Flow – parallel to straight isobars when forces are matched

Surface Wind

Lower 3000ft of atmos = friction layer

Land = wind reduced by 2/3^rd, veer by 30°
Sea = wind reduced by 1/3^rd, veer by 10°

Abv friction layer = wind tend to flow parallel to isobars (gradient wind).

At equator, wind tends to flow perpendicular to isobars due lack of Coriolis deflection.

Sea Breeze

Day -> land heated more = rising air over land and draw in from sea

Land Breeze

Night, sea stays hotter due specific heat. Rising air over water, DRAWS FROM LAND

Katabatic Wind

Clear night sky, air in contact w/ mountain side will cool by conduction. Inc density = air flow down mountain

Anabatic Wind

Day, surface of mountain side may heat by contact conduction = reduced density -> air rises upslope

Cloud

Water vapor condenses into small droplets of liquid water / ice crystals suspended in atmos

Cirrcus – threadlike, hairy, fine
Cumulus – heaped / towering
Status – sheet / layer
Nimbus – rain

• Low Etage (below 8500ft)
• Cu Cumulus (heaped / towering cloud. Rain / snow)
• Cb Cumulonimbus (towering TS. Heavy showers, hail, snow)
• St Stratus (low sheet cloud. Drizzle)
• Sc Stratocumulus (sheet heaped / towering cloud. Drizzle)
• Ns Nimbostratus (sheet heavy rain. Continuous rain / snow)
• Middle Etage (8500ft – 20000ft)
• As Altostratus (heaped middle level cloud. Rain / virga)
• Ac Altocumulus (No rain usually)
• High Etage (above 20000ft)
• Ci Cirrus (fine strands, hooks, clumps of cloud)
• Cs Cirrostratus (sheet of fine hairy, wispy, thread like cloud)
• Cc Cirrocumulus (cirrus forming in elements / lumps)

Special Mentions:

Castellatus – associated w/ altocumulus. Number of turret / cumuliform connected by common base. May signal TS

Type of cloud which forms depends on stability / instability of atmos + air lifting mechanism, causing it to cool adiabatically (due change pressure).

Lifting Mechanisms

• Convection – warm air rise due surface heating. Cumuliform cloud. Cumulonimbus if vert dev. continue
• Turbulence – air rise due surface friction as wind blows over uneven surface. Low lying cloud base may form as water condenses in up currents, evaporates in down currents.
• Orographic Uplift – Air forced over mountain cools adiabatically
• Stable – Stratus (lens) / nimbostratus (w/ heavy rain)
• Unstable – cumuliform
• Mountain Waves – Orographic uplift forces over Mt range. Needs wind blowing right angles to range, speed inc. with height to at least 25kts at top of range, and stable layer (I.e. inversion) abv range. Cloud form crest, ragged rotor cloud may be present under lenticular cloud in rotor zone
• Frontal Uplift – 2 air mass w/ different temp = warm air lifted over cold. Boundary masses = front. Normally LP systems.
• Cold Front: Fast moving cold = unstable conditions ahead. Passage of cold front in SH:
  • Fall in temp
  • Backing of wind
  • Rise in pressure
• Warm Front: Warm air rises up over receding cold. Stable so stratiform cloud, rain from nimbostratus. Approach of warm front = high lvl cloud, followed by mid lvl cloud, then nimbostratus
  • Rise in temp
  • Backing of wind
  • Fall in pressure
• Occluded Front: Cold front has caught up to warm. Both warm + cold type weather. Cloud + rain
• Quasi-stationary: could front and warm meet from diff directions

Synoptic Charts

Synoptic Met – study of pressure pattern chats. Large scale weather patterns / systems

Air Streams

• Warm Air Streams – come from warm source region, generally northerly component (flowing south). Latitudinal cooling surface layers (while upper stays warm) = inversions + stable conditions
• Cold Air Streams – flow from cold source to warm. Sth Hemi = cold streams have southerly component (flowing north). Latitudinal heating warms surface layers (upper is COOL) = steep ELR, unstable
• Inter Tropical Convergence Zone – boundary b/w airstreams from N and S hemispheres, near equator

Pressure Systems and Weather (SH)

Highs (Anticyclones)

• Subsidence, subsidence inversions (limits cloud development, stable conditions).
• Visibility = poor due trapped pollutants.
• Stratiform.
• Light winds, variable near center, blow anticlockwise around high.
• Friction layer, winds blow across isobars
• Aloft winds tend to be gradient (blowing parallel to isobars)

Lows (Depressions)

• Rising air / convection
• Instability brings cloud + rain
• Vis generally good
• Winds clockwise around low, gradient aloft, slightly across isobars and in near surface
• Isobar spacing is closer compared to high

Col

• Neutral area b/w two highs and two lows

Streamlines

Used on synoptic chart in place of isobars. Show average wind direction (no wind strength)

Tropical Cyclones

Intense LP area. Gale force winds (34kts+)

Energy comes from heat stored in tropical waters, and from release latent heat during condensation + cloud form

Generally form 5 – 15° N or S of equator. Rarely form w/I 5° due lack of Coriolis force

1. Formative Stage – existing depression deepens. Wind speed reaches gale. Eye forms (calm center)
2. Immature Stage – pressure fall < 1000 HPA. Hurricane force winds (64kts). Spiral bands form. 30-50km Rad
3. Mature Stage – pressure steady. Area of storm expands. Hurrican winds extend 300km from eye. In SH, most destructive quadrant in front left
4. Decaying Stage – pressure rise. Storm area contracts. If land encountered = cyclone weakens into rain depression. Rain decreases as cyclone moves inland

Australia – Nov to April (when Equatorial trough is in region)

Weather

Fog

Cloud @ ground lvl
Vis < 1000mt, relative humidity near 100%.
Formed -> air cooled b/w dew pt (sat + cond)

Fog produced by radiation (air close to ground, strongest clear nights w/ moist air and inversion. 6kt will deepen fog), advection (warm moist air over cool surface. Eg. Sea blowing over cold land / ocean current)

Fog dissipates when air temp is raised abv dew point / air mixes w/ drier air
Mist

Vis > 1000mt, relative humidity lower than 100

Thunderstorms

Need unstable conditions (i.e. large ELR), much water vapour / humidity, lifting mechanism to trigger convection (e.g. heat, front, terrain, convergence)

1. Cumulus Stage – starts w/ cumulus cloud. Only up draughts present. Cloud warmer than enviro (vert dev)
2. Mature Stage – High cloud, cumulonimbus cloud w/ anvil shaped top. Top of anvil is blown flat by wind, indicating direction. Precipitation falls generating downdraught, with up draughts still present (3000fpm) = wind shear + severe turbulence. Ahead storm = drop temp + gusts. Roll cloud detach and move ahead
3. Dissipating Stage – Up draughts die = rain. Cloud breaks up. 60 minutes in total

Frontal / Squall line – instability b/w two air masses. Most hazardous. Roll clouds associated

Air mass TS:

• Orogrtaphic TS
• Cold stream TS – cold air stream flowing over war surface = warmed from below = instability lower lvls
• Night Equatorial TS – tropical regions. Cloud tops cool due radiations (steep ELR) = TS
• Shear TS – wind shear effect, increase TS activity. May dissipate storm, may spread storm horizontally if vert development is strong enough -> reducing friction b/w up/down draugts = stronger turbulence!

Thunderstorm Hazards

SEVERE TURBULENCE mainly
Turbulence = always associated w/ TS activity, even above the storm
Divide wind speed at cloud top by 10, then times by 1000 for safe alt above storm to avoid turb

Severe icing middle of storm (particularly around freezing level)

Hail likely b/w 10,000ft – 30,000ft

Tornadoes

Usually associated w/ severe TS.

Dust Storms

Need source of dust, uplift mechanism, unstable enviro to keep dust aloft

Jet Streams

Fast moving narrow currents near tropopause (nb, trop varies latitude). Strong horoz wind shear. Speeds 150kts.
Generated by advection of upper air in global circulation pattern + thermal wind gradients produced by temp differential over different parts of earth surface. Roughly E/W, westerly winds. Two Major streams:

Sub tropical jet = 30° S
Polar front jet = further south at polar front

D b Greatest difference b/w actual and gradient wind at 5000ft agl – 5 ° S

Hazards

• Wind Shear
• Horoz through inversion
• Low lvl Jet
  • Fast moving stream low lvl.
  • Air circulating around a high hits mt. range -> focused into narrow stream around range
  • SURFACE INVERSION MUST BE PRESENT.
  • Max wind in early morning when surface inversion = strongest.
  • Main hazard to ac is strong horizontal wind shear
• Turbulence
• Vert Wind shear
• Convective Turb
  • Rising air currents (i.e. blw cumulus/numbus cloud)
• Mechanical Turb
  • Wind blowing over surface obstructions.
  • Severity depends on wind speed, height obstruction, surface roughness, stability atmos.
  • Stable conditions = lee side turb
  • Lee turb = less in unstable conditions as rising air lifts turb air.
  • Mt waves = example lee turbulence
• Frontal Turb
  • Wind shear boundary two air masses different temp (density)
• Icing
• Hoar Frost
  • Light frost when ac skin below 0 in high humid cond.
  • No weight, but airflow interruption.
  • Can occur in flight through warm moist layer.
• Rime Ice
  • Supercooled water drops freezing on impact.
  • Pockets air may be trapped, making opaque / brittle
  • Most common range = -10° to -20°.
  • Stratiform cloud usually (small drop size. No nimbo)
• Clear Ice
  • Slow freezing large super cooled water drops.
  • Range 0° to -15°
  • Most dangerous! Difficult to remove, heaviest, sig red. aerody efficiency.
  • Most common cumuliform clouds abv freezing lvl. Also possible in thick altostratus and nimbostratus. Orographic cloud also likely to produce clear due large drop size
• Carby Ice
  • Formed in venturi of carby
  • Intake air -> cooled by fuel evaporation / loss pressure
  • Possible large range temp, humidity must be high
• Visibility
• Greatest horizontal vis over ½ or more of horizon measured from eye lvl
• Measure air transparency (not light lvl dependent, same vis at night)
• Slant / oblique visibility will be worse than vertical
• Microbursts
• From base convective cloud.
• Often from squall lines and TS activity. May be associated w/ virga
• 15 min from ground contact to dissipation.
• CYCLE ->

Icing By Cloud Type

Cirrus, cirrostratus – no icing (cloud is ice crystals)

Cirrocumulus – rare (main ice crystals)

Altostratus – light rime ice may occur (cloud consists mainly supercooled water drops). Prolonged flight = buildup of rime ice = hazard. Clear ice is possibility in thick altostratus

Altocumulus – if cloud = thin, light rime ice may occur. Usually turbulence here = supports larger supercooled drops. Build up rime ice may be more rapid, greater possibility ice forming

Stratus – in AU = temp above 0° = no ice. If below freezing, light rime ice. Lack turbulence = no large drops (no clear)

Nimbostratus (orographic) – supercooled rain common. Clear ice real risk up to 5000ft abv freezing lvl (abv = rime)

Stratocumulus – Rime ice if temp < 0. Usually only present over Tas and S vic in winter

Cumulus – Small will usually be abv 0. Large = clear ice 5000ft abv freezing (rime ice abv)

Cumulonimbus – large supercooled drops at and above freezing lvl. Freezing level up to -15° = clear ice certain. Rime ice above this up to lvl where ice crystals predominate.

SOME RISK OF ICING EXISTS AT ALMOST ALL LEVELS IN CUMULONIMBUS CLOUD

1. B C – wording of question. AROUND a storm could be hail and turbulence
2. C D – be 20 nm from TS!!
3. A C – Light wind in radiation inversion will make inversion weaker, but more deeper

Aviation Forecasts

Go Over GAFS HERE

SIGMET / AIRMET

Pilots transmit AIREP if not in forecast.

For significant but moderate conditions blw 12,000ft = AIRMET advice is issued
For severe and/or widespread conditions = SIGMET advice issued

Remember

Inter/Tempo is DDHH (0112 etc)

TAF

5NM coverage from ARP

TAF issue time is DDHHMM (TAF YSWG262206Z)
Usually valid 12 hrs (can be longer/shorter – most capital city = 30 hrs)

VALIDITY – after Issue time in format DDHH (2700/2712)

WIND – direction T FROM witch wind blows. If max speed is 10kts greater than mean wind = gusting
Calm = 00000kt

VIS – 9999 = 10km grater

CLOUD – 008 = 800ft. 110 = 11,000ft
TCU = towering cumulus
CB = cumulonimbus

Vert Visibility – VVhhh (hhh = vert vis in hundreds feet)

CAVOK:

• Vis 10km +
• Nil sig cloud (no cld blw 5000ft AGL, no CB / TCU)
• Nil significant weather

TAF FM / BECOMG tags:

• NSW (weather)
• SKC (sky clear)
• NSC (cloud) used to indicate improvement

PROB – 50% / higher = included in TAF

RAINFALL – RF00.0/021.4 = first three = rainfall last 10 min. Last 4 = rain since 0900 local to nearest 0.2mm. e.g 21.4mm rain since 9 am

TEMP / QNH – 3 hrs apart, beginning from the issue time / hour.
Linear interpolate b/w times: temp round up if decimal, QNH round down
Negative temp = M before temp value

Aerodrome Reports

METAR / SPECI

Indication weather in vicinity (8km – 16km ARP)

Reports of observed conditions at given time (NO VALIDITY PERIOD), not forecasts

May be made by observers / automated (will display AUTO after date/time. If AUTO, will read No directional variation (NDV) after vis reading)

METAR – routine observations, usually each hr / ½ hr when weather conditions are abv specified minima
SPECI – special observations below specified minima

Will give temp/dew point in that format

TTF

Observed weather conditions expected to continue w/ no significant change for coming 3 hrs

Can be TTF METAR or TTF SPECI (standard METAR / SPECI which have a TTF appended to them)

Valid 3 hrs, supersedes TAF for this period

NOSIG = no change in conditions expected

Upper Level Meteorology

True Alt

Pressure decrease 1HPA / 30ft up to 5000ft (rate reduction decreases after, i.e. FL400 = 1HPA / 100ft)

Vert distribution pressure in atmos = depends temp (colder column air will be more dense than air standard temp. Upper lvl pressure will be less than in standard column). THUS -> altimeters are based off ISA so will read incorrect if air parcel is colder / warmer.

Colder than ISA = altimeter sense lower pressure -> over read (High to low, watch out below). Will think ur higher

Flight computer -> set current OAT at particular pressure height in window, then reading true Alt on outside wheel against calibrated / indicated alt (altimeter readout). Note, take care with the negative temps to left!

Can use rule -> Alt error ~ 4% of indicated height per 10° of variation from ISA
e.g. conditions ISA-20, alt error = 8% of indicated height, and true alt will be lower than indicated (alt over reads)

NB – when operating with local QNH for airport -> altimeter error due ISA variation = only applicable to HEIGHT ABOVE AIRPORT (AGL error only). No error on altitude below QNH datum (ap elevation). Local QNH cancels out any error up to lvl of airport and alt will read elevation of ap on landing

If on Local QNH and airport is abv sea lvl

e.g. 10,000ft on main alt on local QNH above 8,000ft elevation ap, local ap temp 20°. First calc the error for the 2000ft (pressure alt AGL is 8,000ft with 20° ISA, then 2,000ft on indicated height = 2,140ft true alt (above AGL, so true alt of aircraft = 2,140 + 8000 = 10140ft)

If local QNH is not avail at high elevation aerodrome = significant alt error is possible if temp is not close to ISA

Tropopause

15 to -56.5° to tropopause (36090ft)

Temp remain constant until 66,000ft = increase

NB: tropopause is defined by abrupt / definite change from steady ELR to constant temp

Jet Streams

Breaks in tropopause. Jets narrow air along horizontal axis in upper top or stratosphere

Wind speeds 60kts+. Extend thousands meters horizontally, less 100nm wide, only several thousand feet deep

Dominant stream is westerly in each sphere.

Often associated w/ clear air turbulence due wind shears.
Most severe CAT polar side of jet stream blw lvl of core, also in winter (jet = stronger), and over land / jet is curved
CAT usually only apparent for 1-2 thousand ft thick (change IFR lvls should be sufficient)

Pressure distribution upper levels = temp distribution. Polar column = cold. Equatorial column = warm. At surface, pressure is equal in both columns. Increase height = pressure warm column is greater than colder at given height

This creates jet from temp differential. Pressure gradient wind blows towards cold column (S in SH). Know as thermal wind (temp diff b/w two columns). Coriolis effect = deflected left resulting in Westerly wind in BOTH HEMI
Gradient intensity increases up to tropopause = greater wind speed.

Isotachs joining points of equal wind speed show max wind speed in jet core

Lower tropopause over poles = temp stops lapsing earlier thus temp relatively warmer abv polar trop than equator
This can create reversal thermal wind, blowing wind N (deflected Left = easterly wind abv tropopause).

Sub Tropical Jet = 200HPA (FL385) ~ 30° lat
Polar Front Jet = just b/w tropopause above the 500HPA position of polar front

These patterns follow circulations during seasons (summer = south in summer etc)
Sub front jet is more mobile, following position of polar front. Can merge with sub tropical jet. STJ is usually stronger

If OAT drops when flying S in SH = still below tropopause (and jet)
OAT rises flying S = above tropopause (and jet stream)
Opposite applies when flying North, or in NH

CONSTANT OAT when flying in either direction indicates possibility flying through jet stream core

Upper Level Charts

FL185 upwards