Facts Flashcards
What types of cloud are tornadoes associated with?
Cb (mature stage of TS)
What time of year are tornadoes most likely to occur in North America?
Spring and early Summer as cold polar air is moving over a rapidly warming land mass
Diameters of a typical tornado?
tens or hundreds of metres
What is the lifespan of a tornado?
up to thirty minutes
What is the lifespan of the mature stage of thunderstorm?
up to an hour
What is the speed of movement of a tornado?
30mph
What is the name for a tornado over the sea?
A watersprout
What is the name for a tornado over the sea?
A watersprout
How do tornados move?
With the TS they are associated with
Typical windspeed inside a tornado?
300mph
What kind of pressure at the centre of a tornado?
Very low
What is an area typically associated with Tornados?
central plains of the USA
What is a funnel cloud?
A tornado type cloud that does not reach the ground.
What conditions trigger tornados?
Very large Cb clouds
What is required for very large Cb?
moist, unstable air and convective lifting
What is a watersprout?
similar to a tornado but takes place over the sea and does not reach the same intensity.
What is the name of the Cold Air Outbreak in Australia?
Southerly Buster
What is the name of the Cold Air Outbreak in South Africa?
South Westerlies
What is the name of the Cold Air Outbreak in South America
Pamperos
What is the name given to Cold Air Outbreaks in the NH?
Generic name of Cold Air Outbreaks!
When does the ITCZ pass over the equator?
Spring and Autumn equinoxes
When are the spring and autumn equinoxes?
March and September
When are the long rains?
April (the spring equinox)
When are the short rains?
October (the autumn equinox)
Where does RVR appear?
Only in METAR, it is not forecast.
What is the size of drizzle
Between 0.2mm and 1mm diameter
What are ice pellets?
precipitation which leaves the clouds as liquid (i.e. rain or drizzle) and freezes as it falls through a cold layer
What is the difference between ice pellets and hail?
Ice pellets are formed outside of the cloud while hail is formed inside the cloud.
Size of raindtrops
1mm to 5.8mm (bigger drops would break up)
How is hail formed?
Ice Crystal at the top of the cloud falls and gathers moisture as it does so.
Which cloud is Hail associated with?
Only Cb..
Where will the largest hailstones be found?
In Cb over continental interiors rather than over the sea because the convective and orographic triggers will be stronger over the land than sea.
What is the consequence of a very high freezing level (16,000ft) in equatorial regions?
Hail will melt before it reaches the ground
Highest level of encountering hail?
Up to 45,000ft
How long is the dissipating stage of a Thunderstorm?
about 2 hours typically.
Why is the anvil created?
Upper winds spread the ice crystals
Formula for PGF/Isobar spacing?
PGF = 2wVp Sin ( Lat )
What causes a halo around the sun or moon?
Refraction of light passing through ice crystals of cirrostratus on a warm front.
What is a blocking anticyclone?
A WARM quasi-stationary anticyclone that has broken away from the Azores high can disrupt the passage of the travelling lows over the North Atlantic and their associated fronts. The influence of warm highs extends into the upper troposphere these stable features will affect the sub tropical jetstream often changing its direction to flow north/south for thousands of miles. Can lead to heat waves in summer and long periods of cold weather in winter.
What is the temperature of a blocking anti-cyclone?
WARM!
What type of cloud does drizzle come from?
Stratus
In general is visibility greater in rainfall or drizzle?
Greater in rain as small water droplets in drizzle indicate very little lifting action but greater size raindrops indicate more lifting action and unstable air. Unstable air clears pollution vertically so visibility is better
Where does coalescence produce only very light rain or drizzle?
Mid-latitudes
What is the most northerly latitude of the ITCZ in July over Africa?
15°N
What is the final northerly position of the ITCZ in July in China?
30° - 35°N
When are there more warm occlusions?
WINTER
When are there more cold occlusions?
SUMMER
Where is the sub-tropical high pressure belt located?
Centred around 30°N / 30°S
Formula for Tailwind or Headwind?
Cos (angle) X Speed
Formula for hPA decrease with altitude?
96 * (Temperature (°K) / Pressure (hPa))
Formula for RH
100 - 5 (Temperature - Dew Point)
What are the locations of the 0° isotherm?
Poles = Ground level
Temperate Latitudes = Ground to 10,000ft
Tropics = 10,000ft - 16,000 ft
What are the locations of the -45° isotherm?
Arctic - 18,000ft over India
Equator - 37,000ft (Jan) - 40,000ft (July)
How do you convert between Kts and Km/h
1.85
What is the visibility for fog?
< 1000m
What is the visibility for mist?
1000 - 5000m
What are the amounts that the surface wind will differ to the free flow wind?
Over land, 30° and 50%
Over sea, 10° and 70%
What are the amounts that the surface wind will differ to the free flow wind?
Over land, 30° and 50%
Over sea, 10° and 70%
What is the cause of convergence around a low?
Surface friction
What is the cause of divergence around a high?
Surface friction
What happens to he pressure change across 100m as you go up in the atmosphere?
As you go higher up there is less change in pressure per 100m
What happens to he pressure change across 100m as you go up in the atmosphere?
As you go higher up there is less change in pressure per 100m
What wind speeds are typically quoted for radiation fog?
2 - 8 kts
What winds are are typically quoted for advection fog?
15 Kts
Formula for Density?
Density = Pressure / Temperature
What is the average height of the tropopause?
11km
What is the height of the tropopause in ISA
11 KM
What is the average atmosphere condition?
Conditional instability
What is the average atmosphere condition?
Conditional instability
How do we find the actual ELR?
Use of a raido sonde.
What does the wet bulb, dry bulb spread tell you?
About the humidity of the air
It indicates RH
What is the hair hygrometer used for ?
To measure humidity
Where does the wet bulb temperature lie?
Between the dew point and the OAT
What is a psychrometer?
A wet bulb and dry bulb thermometer together
What is the SVP over ice compared to supercooled water?
SVP less over ICE than over supercooled water at the same temperature
What does SVP depend on?
TEMPERATURE & SURFACE
What conditions do we expect to find the middle of a warm sector?
Tropical Maritime
low stratus, poor visibility, drizzle
In summer the cloud may lift and disperse but in winter the cloud base would remain low over the land
What conditions are likely for the formation of mist/fog?
Temperature & dew point close together
What is the Mediterranean climate?
Hot dry summers and cold wet winters
When does freezing fog exist?
if the fog droplets are supercooled.
Where do we find the squall line?
Ahead of a cold front
What is a squall line?
A line of Cb associated with an advancing active cold front
What is a squall?
An increase in wind strength lasting for several minutes.
Describes the increased wind produced by the gust front which precedes a TS
What will happen when flying into freezing or supercooled rain?
Clear ice will form
The pressure group in a METAR message represents what?
The QNH rounded DOWN
What are the relative speeds of the cold and warm fronts?
The warm front moves at about 2/3 speed of the cold front
What is the primary use of satellites?
to locate FRONTS in areas with few observation stations
What is the difference between Ns and Cb precipitation?
Ns will give continuous precipitation whereas Cb will give showers
What is the issue with heavy precipitation immediately ahead of an airbourne radar?
It may hide precipitation further away
What might we find in the warm sector in the Summery months?
Fair weather Cu
What does AIRMET apply to?
Low level operations only
Below FL100 or FL150 in mountainous areas
What is MWO?
Meteorological Watch Office
What is a MO
A Meteorological office
What does a WMO issue?
AIRMETs and SIGMETs
What does a MO issue?
Aerodrome forecasts and briefing documents
What is VOLMET?
HF and UHF
METAR & TAF
How is Temperature and Dew point rounded in METAR?
Rounded UP Up Up
** Careful of rounding negative figures **
How is sustained windspeed measured?
average of 10 minutes
Tropical Storm windspped?
> 33 Kts
Cyclone/Hurricane/Typhoon windspeed?
> 63 Kts
Relationship between cloud bases and wet/dry bulb temperatures?
the further away the wet bulb and dry bulb temperatures the higher the cloud base will be.
What happens to windspeed at latitude increases?
Decreases
Consequences of sinking air?
Dissipate cloud and trap pollution, giving poor visibility
Where do the trade winds blow from?
Sub Tropical Highs
What kind of fog might you get on either side of a warm front?
frontal fog ahead
advection fog behind
What is a cold air pool?
very cold upper air and warm surface air
What does a stormscope detect?
Electrical discharges
Mean temperature in polar climates?
+10
What is the typical latitude of the prevailing westerlies?
40° - 60°
Where does a microburst occur?
Under a TS
What causes frontal fog?
high relative humidity
What is a consequence of frontal fog
reduction in visibility
What is mixed ice?
mixture of rime ice and clear ice
Where is rime ice typically found?
In Ns
What weather is associated with a stationary high pressure region over land in the winter?
High pressure is associated with stable, sinking air. Without convective or frontal lifting there will be little or no cloud and precipitation. Any cloud formation in winter will be stratus rather than cumulus and the precipitation will be drizzle (or granular snow) rather than rain (or snow).
What is a stable layer at some height in the low troposphere of an older high at mid-latitudes?
A subsidence inversion
Which clouds can produce large water droplets?
large Cu which will contain both water droplets and ice crystals
What can occur over land in a col in summer?
Air Mass Thunderstorms
Lack of turbulence –> surface heating –> convective activity
Isolated, Thermally generated CBs across the area
What can occur in a col in winder over land?
Radiation fog
What are the typical col conditions?
light winds, clear skies, inversion at low level
What are the ATIS wind direction?
Magnetic
What will a sea breeze do in the NH?
Veer and increase in strength by the afternoon
What is the minimum Jet Stream speed?
60 kts
What does adiabatic mean?
heat does not enter or leave the system
How long does TEMPO last for ?
no more than one hour on any one occasion and the total time spent in those conditions will not add up to more than half the period
When will gusts be reported in a metar?
when the gust is at least 10 Kts more than the wind
METAR validity
only at time of observatoin
What does a SNOWTAM include?
information abut breaking and runway surface contamination
Where does breaking information occur?
in the supplementary info in ATIS & METAR
Where do the feathers on the wind arrow point?
towards the low pressure
What is a polar low?
small short lived depression that can bring frequent heavy wintery showers esp costal areas
Where does the sun set?
In the west in both hemispheres
PIREP
SPECIAL Air report
AIREP
Routine Air report
Polar ice cap is the source of which kind of air?
Arctic
When does a thermal low form?
Strong surface heating
Can a thermal low form over land?
Yes
Can a thermal low form over sea?
Yes
Can a polar low form over the land?
No
Can a polar low form over the sea?
Yes
Where does a polar low normally form?
the the arctic Maritime airmass over the North Atlantic Ocean
When does Rime ice form?
less that -7°C in Stratus and less that -23°C in Cumulus
When is there no risk of icing?
less than -45°C
When does hoar frost form?
when the airframe is at a temperature below 0°C and it climbs into warmer, moister air there will be direct sublimation => HOAR FROST
How does hoar frost form
Water vapour turns directly into water droplets on the aircraft surface: Sublimation
How much should you avoid a Cb by?
5000ft and 10NM normally
what are the air masses that are observed most frequently over Europe?
maritime Tropical and maritime Polar
How often does the airfield windshear alert system update?
every minute
Where do easterly waves form?
Close to ITCZ
5° - 20° N/S
What weather is associated with an easterly wave?
Severe weather;
A line of Cb and TS aligned N - S from TRAILING EASTERLY EDGE
What is a line of active Cb know as?
A tropical tornado
What percentage of easterly waves turn into TRS?
1/10
What is an easterly wave described as?
A ripple in the isobars which are otherwise parallel to the ITCZ
What kind of pressure is associated with an easterly wave?
a trough of low pressure
Where is the polar front jet stream speed greatest?
Between a trough and a ridge
Strongest wind will occur where you have the greatest difference in temperature and pressure
How much should you avoid a TS by at FL300
20NM
What is rain ice?
a form of very heavy clear icing encountered when aircraft are flying the rain ice triangle
How server is the rain ice?
Very; rain is just supercooled before hitting the aircraft, giving the worst possible clear ice with a high rate of accretion
What is the visibility in a heavy dust storm?
< 500m
What causes a sea breeze to veery?
As the breeze develops, the Coriolis force causes it to veer
Where are blocking anticyclones located typically?
between 50°N and 70°N
What wind do the isobars indicate?
the free flow wind, the surface wind will back compared to this
What does the advection of warm air aloft indicate?
- indicates the approach of a warm or cold occlusion
- both in NH and SH
When can lightning appear in a thunderstorm?
Mature stage
What causes lightning?
Build up of electrical potential in the cloud; upper cloud collects a positive charge while the lower cloud collects a negative charge - at a critical level this discharges as lightning.
What does a doppler radar do?
Record the movement of raindrops so do show turbulence in cloud
What can be expected around areas of convergence and divergence associated with a low?
Turbulence, Convergence results in cloud but divergence does not likely to be CAT over the divergence area
When can advection fog be formed?
Day OR Night
Visibility in blowing snow?
Whiteout, down to virtually zero
What are the characteristics of stable air?
Poor visibility and stratiform cloud
DALR close to SALR
just below tropopause where cirrus is found
Where is mixed ice normally found?
Ns
What is the vertical structure of the atmosphere?
What is the Tropopause height at different latitudes?
What are the DALR, SALR and ELR?
What is the Harmattan?
Dry, dusty, NE wind from the Sahara [ITCZ RETREAT]
What is the Haboob?
Sand storm associated with TS in Sudan
What is an example of a Foehn wind?
Chinook, [ Canadian Prairies]
What is the Mistral?
Northerly, from France, blowing from RHONE VALLEY, and past FRENCH ALPS. Valley wind with Katabatic enhancement (winter)
What favours the formation of the Sirocco?
Low pressure area in the Med.
What are the characteristics of the Sirocco, Ghibli and Khansin?
Dry, dusty, stabe. Blow out of the WINTER high pressure area over the Sahara in N Africa. Cause gradient wind dust storms from Algeria to Egypt. Sirocco may reach across Med to Europe bringing low stratus, advection fog and drizzle
What is the Bora?
Cold northerly, pure katabatic wind [ALPS]
Funnelled into river valleys
blows down mountains
comes out at Adriatic over Trieste
Are cold air pools more prevalent over land or sea?
Land
How long does a cold air pool usually last?
for the life of the system they are sitting above
diameter and lifespan of typical microburst ?
4km and 1.5 minutes
