OCEANIC MET Flashcards
Why is the suns heat distributed differently over the earth?
Because in some places it hits on an angle due to its spherical shape and the physical distance due to earths tilt (23 deg)
What is the sub tropical jet?
The high level winds from the Hadley cell accelerate towards the pole and turn left due to coriolis being greatest at the poles.
What is the polar jet stream?
- powerful upper-level winds that sits above/between the boundary of cold polar air (polar cell) and warm mid latitudes cell
- Temp contrast of the two cells causing a pressure gradient N to S in Southern Hemisphere (turns left due coriolis to become a westerly)
- The bigger the temp contrast the stronger the jet therefore it’s stronger and further north in the winter as the poles cool significantly
What is a monsoon?
A large seasonal sea breeze
Differential heating between land and sea on large continents cause large scale pressure gradients
What is the equinox?
the time or date (twice each year) at which the sun crosses the celestial equator, when day and night are of equal length (about September 22 and March 20).
How are rotor zones formed?
Wind forced over terrain with a stable layer on top creating waves on the other side
At the troughs are low pressure systems and peaks highs
This causes wind at low level to reverse direction travelling from low to high pressure.
How is lightning made?
Negative is hail and positive is relatively lighter ice crystals
What is a weather bomb?
A low in which the pressure drops rapidly over 24hr
Associated w terrible weather
What is a solar flare?
gases and charged particles or electromagnetic radiation expelled above an active sunspot, can cause space WX events & disrupt comms (esp HF)
What causes the inversion in the stratosphere?
The stratosphere contains the ozone layer and converts UV light to heat = TEMP INVERSION
When is monsoon season?
May-July in northern hemisphere
November-feb in southern
What is Buys Ballot’s Law?
In the Southern Hemisphere, wind at your back means low to your right.
Southern occillation
Takes about 4 years per cycle
High maintained by cold ocean temps
What is normal and severe WINDSHEAR?
Normal-rapid change in wind direction effecting airspeed greater than 10kts
Severe-greater than 14kts or vertical speed changes greater than 500fpm
What effects surface pressure systems
sea currents, land masses, water vapour etc
List the general circulation
Polar high Polar easterlies Polar Lows Westerlies Polar fronts Mid-latitude anticyclones Trade winds equatorial trough
What is the tropcial/Hadley cell responsible for? Where is it located?
Between the equator and 30deg
Responsible for transferring large amounts of fast moving equatorial air to higher latitudes, where it converges & sinks
How does temperature difference in ocean currents affect pressure?
Colder temperatures = surface highs
Warmer temperatures = SFC lows
What is the walker cell? Where is it located?
- A semi-permanent high pressure system in the eastern pacific off the coast of Peru.
- Formed & maintained by the cold Humbolt current (flows up from the southern oceans)
What is the ITCZ
Location
formed by
- Inter-tropical convergence zone
- Located along the equator - top of Aus to the top of africa
- formed by the clash of SE trade winds from the southern hemisphere & NE trade winds from northern.
What does the ITCZ result in?
Results in upwards/ motion over a vast area with heavyb rain & violent TS activity.
What is the SPCZ
Location
formed by
- South pacific convergence zone
- Runs from the pacific (cook islands ish) out to well off the East coast of NZ.
- Forms when mid latitude westerlies clash with northerly outflow of the walker cell.
What does the SPCZ result in?
Frequent TS activity, birth place of TC in south pacific.
What is the position of the SPCZ controlled by?
by the size of the walker cell (and therefore the size of the humbolt current)
When does El nino occur
When the peruvian current fails at the SFC & is replaced by warmer sea temps (less density at SFC). This lowers east pacific pressures, therefore shrinking the walker cell & allowing SPCZ to move east.
What occurs for NZ when El Nino is in effect
Stronger W - SW flow over NZ = cooler temps & higher rainfall in the south.
TC are more likely to occur in the cook islands & tahiti.
When does La Nina occur
Colder & stronger peruvian current, intensifies the walker cell & moves SPCZ towards NZ.
What occurs for NZ when La nina is in effect
Warmer temps & more rain in North. Northern NZ experiences more cyclones
NZ summer
SPCZ & ITCZ move further south, zone of westerlies & polar lows that are responsible for the cold also move Sth. Weather is slower moving
NZ winter
Anticyclone centre moves further north, polar lows affect NZ more with sharp frontal transitions moving quickly across the country.
Environmental lapse rate
Actual rate of temp change with altitude
DALR
Rate ar which a parcel of air cools as it rises upwards (3deg/1000ft)
SALR
1.5deg/1000ft
Standard atmosphere
15dec C
- 25hpa
- 98deg/1000ft
- 225kg/m3
Describe conditons that cause fog in WP
<5kts, temp & dew point within 1-2deg, around 4deg C
What is the tropopause
Atmospheric boundary between troposphere and stratosphere.
Abrupt change in ELR, temps stop decreasing and remains steady
How does a sea breeze form
- Land heats up faster than water = thermal exapansion & High pressure aloft
- Pressure gradient H - L created
- shift of air with pressure gradient & more heating = low pressure at SFC
- cycle created
How does a Katabatic form & what is it
A katabatic is the carrying of high density air down a slope under gravity.
- light wind
- clear nights
- sloping ground
- slack pressure gradient
What are Isobars
Lines that connect points with the same pressure
What is a Fohn wind, how is it formed
- A dry, warm downslope wind in the lee of a mountain range
- formed due to differing Adiabatic lapse rates (DALR/SALR), adiabatic warming of air that has dropped all moisture on the windward side = hot dry winds in lee
What are lenticularis clouds
Wave clouds formed in the lee of mountains when strong winds going up and over terrain form a train of cyclic waves downstream. If there in enough moisture, clouds will form at the top
Pressure lapse rate for every 1deg from ISA
120ft
Dewpoint decreases ___deg/1000ft
0.5
Define meteorology
Study of earths atmosphere and how it interacts with the surface of the earth
Describe a depression
Area of relatively low pressure, identifying features include circular and concentric isobars centered around a point with the lowest pressure
CLOCKWISE WINDS IN SH
Describe a tropical cyclone
Tropical depressions form into tropical cyclones, close isobars = high winds, warm cored & lots of moisture
What is a trough
Extension of isobars away from centre of Low pressure. Pressure at any point along the trough is lower than it is either side.
Sharp change of wind direction
Describe an anticyclone
Area of high pressure with circular & concentric isobars surrounding centre where pressure is highest
Lighter winds
Anticlockwise in SH
Ridge of high pressure?
Extension of isobars away from the centre high, any point along ridge is higher pressure than either side. Never marked on charts
What is a COL
Even pressure between two highs/two lows, light/variable winds.
Along axis however, converging winds and moisture = TS
Describe pressure gradient
Spacing of isobars
- Closely spaced = pressure changes rapidly over short distance = strong winds & vice versa
Weather associated with a H
- settled weather
- light wind but can be stronger towards edges
- good vis but can be hazy
- patches of drizzle & fog in AM
Wx associated with a L
- unsettled weather
- strong winds
- reduced vis, esp in frontal rain
- heavy rain in centre & following fronts
METAR issued?
METAR AUTO?
Every hour
Every 30mins
When is a SPECI issued? (3)
When Wx deteriorates beyond;
- sig wind change
- cloud base red to <1500’
- vis red <8000ft
Issued at times other than the top of the hour
TREND?
Forecast appended to METAR/SPECI, valid for 2 hours and takes precedence over TAF
TAF?
Forecast wx conditions within 8km of A/D
Domestic is valid 12 hrs. International valid 24H
Issued 0600, 1200, 1800, Midnight
Fog, mist & haze parameters
- FG: vis <1000m
- BR: 1000-5000m
- HZ: <5000m
How long does a TEMPO period last
less than 60mins
Forecast area for ARFOR
wind & wx up to 10k ft
What can a sigmet be issued for
SEVERE;
TS, mountain waves, Icing, Volcanic, sandstorm, Turb, TC
Four parts of earths atmosphere most important to earths wx
Water, CO2, Ozone, aerosols
Where is the tropopause
16km equator, 8km poles
Four methods of heating atmosphere (rcac)
- Radiation: from sun
- Conduction: by contact
- Advection: hrizontal transfer by wind
- Convection: movement of mass (e.g. clouds)
3 types of inversion
- SFC radiation: Clear night, light wind = cooler air at SFC than above
- Frontal: Cold front: cool air wedging under warmer air
- Turbulence
QNH
QFE
QNE
QNH: AD pressure corrected to MSL = alt above MSL
QFE: Altimeter set to read 0 at AD level = alt above feild
QNE: 1013, pressure alt
High to low..?
Watch out below (altimeter over reads)
Effect of temp on pressure?
Temp higher, air less dense = lower pressure & vice versa.
Gust?
wind at least 10kts more than mean speed
Squall?
increase of at least 16kts to at least 22kts
Describe coriolis force
an effect whereby a mass moving in a rotating system experiences a force (the Coriolis force ) acting perpendicular to the direction of motion and to the axis of rotation. Means air flowing from equator to the poles in the SH is deflected to the left.
Define wind shear
Caused by?
change of wind speed/direction over short distance due to strong temp or density gradients.
- SFC friction
- TS
- Temp inversions
- Frontal activity
4 categories of turb?
- Convective
- Mechanical
- wake
- CAT
How do southerlies & northerlies relate to stability
- Southerlies: cool air warms up = unstable
- Northerlies: warm air cools down = stable
Types of fog? (3)
- Radiation: cool ground, clear skies, moisture at low level, light sfc wind
- Advection: Caused by horizontal mvmt (moist air onto cold SFC)
- frontal: CLD base lowers to ground
Types of airframe icing (5)
- Rime (small droplets at < -20, freeze on contact) brittle
- Glaze (0 to -20, remain liquid due latent heat release, rolls back over wings & freezes clear)
- Mixed (both above)
- Freezing rain/drizzle
- Hoar frost
Icing most frequently occurs?
Most severe?
-3 to -12
TCu, CB, Lentics, Ns.
Two types of TS?
Airmass: E.g. Convective/Orographic
Frontal: E.g. Cold or warm front
How do TS form
Thermal updraft > water vapour condenses > heavy rain drags cold air downward = cycle created. (1.5hr)
Requirements for TS development
Unstable airmass, moisture, trigger mechanism
Flight condxns associated with TS
sev turb, icing, lighting, gust fronts, microbursts, hail, bad vis, tornadoes
Define a front
The boundary between two airmasses with differing characteristics (temp/pressure).
Define a cold front & characteristics
A front where Cold air undercuts a slower moving mass of warm air.
1. Advancing cold air forces warmer, less dense air upwards.
- This process is fast, and generates Tcu and Cb
Characterised by :
Abrupt wind change, Sharp pressure rise following front, Narrow band of precip
Define the process of a warm front
A front where warm air is forced aloft as it rides up over a slower - moving mass of cooler air.
1. Warmer, less dense air rises over cooler air causing a broad area of cloud to develop ahead of the front. (air rises slower than that of a cold front = Stratiform cloud)
Define an occluded front and characteristics
A front that has both the characteristics of a cold and warm front, and is relatively weaker
- Extensive cloud sheet of Stratiform, thickens and lowers as front approaches
- Long periods of rain, wind change
Define a stationary front
What wx is it associated with?
Any front (cold/warm/occluded), that has weakened and slowed to less than 5kts ground speed.
Associated with loss of original upper cloud sheet, and bands of cumulus and scattered middle cloud
