Upper Level Meteorology Flashcards
What happens to atmospheric pressure as there is an increase in altitude?
It decreases
What is the ISA atmospheric pressure?
1012.25 HPA at mean sea level
What is the atmospheric pressure at each altitude? 5,000ft 10,000ft FL185 FL235 FL300 FL340 FL385 FL445
5,000ft- 850 HPA 10,000ft- 700 HPA FL185- 500 HPA FL235- 400 HPA FL300- 300 HPA FL340- 250 HPA FL385- 200 HPA FL445- 150 HPA
Rate of pressure decrease with altitude gain?
1HPA / 30ft up to 5,000ft AMSL
Not linear above 5,000ft
If a column of air is colder than ISA it will be…
Denser and therefore heavier and pressure will be reduced
If a column of air is warmer than ISA it will be..
Less dense, lighter and have an increased pressure
If pressure is warmer or cooler than ISA will the altimeter be accurate?
No, altimeters are calibrated for the vertical pressure distribution and rate of change in ISA, if it is not iSA they will not read correctly.
What will the altimeter error be if it is colder than ISA?
Senses the lower pressure and consequently indicate a higher altitude than the aircraft actually is
(Overread)
What will the altimeter error be if it is warmer than ISA?
Altimeter will sense the higher pressures and indicate a lower altitude than the aircraft actually is
(Underread)
How to calculate altimeter error caused by temperature variation on flight computer?
Set current OAT at a particular pressure height in the window and then read true altitude on the outside of the wheel against the calibrated or indicated altitude (what altimeter reads) on inside
Altimeter temperature error rule of thumb?
Altimeter error is approx. 4% of the indicated height per 10 degrees of variation from ISA
When aircraft are operating on local QNH for an airport, the altimeter error due to ISA is only applicable to…
Height of aircraft above the airport (AGL Error Only)
- Local QNH cancels out any error up to the level of the airport
What is the ELR?
1.98 rounded to 2 degrees per 1,000ft from a value of 15 degrees at mean sea level to -56 degrees at the tropopause at a height of 36,090ft
After the Tropopause what happens to the temperature until 66,000ft?
It remains constant at -56.5 degrees
What is tropopause defined as?
An abrupt and definite change from a steady environmental lapse rate where the temperature is steadily decreasing with increasing altitude to a situation where temperature remains virtually constant or isothermal (slightly increasing) with increasing altitude
Because of the greater depth of atmosphere in the tropics, the change in lapse rate occurs?
At an altitude above 36,090ft, often as high as 60,000ft
Around the poles where does the tropopause exist?
Often below 36,000ft
Over the tropics, the tropopause has a much … temperature than ISA
Colder
Often as cold as -70 degrees
Where are jet streams often found?
At the breaks in the tropopause
What is a jet stream?
A strong narrow current of air concentrated along a horizontal axis in the upper troposphere or in the stratosphere
What are jet streams characterised by?
Strong horizontal and vertical wind shear and wind speeds in excess of 60kts
How far can jet streams extend horizontally?
Thousands of miles
Usually less than 100nm wide and only several thousand feet deep
What wind speed must be reached to be considered a jet stream?
60kt
Max jet stream speed?
200kt
In each hemisphere the dominant jet streams are…
Westerly and occur at the level of the tropopause
Why are jet streams often associated with Clear air turbulence?
Because of the strong wind shears encountered around them
Where is Clear Air Turbulence considered to be most severe?
On the polar side of the jet stream below the level of core
Is clear ice turbulence usually more severe in winter or summer?
Winter when the jet streams are stronger and when the jet stream is over land and curved
Why do jet streams form?
As a result of upper-level pressure distribution in much the same way as surface winds
How is a thermal wind formed?
Result of the temperature differential between two columns
What is an Isotach?
Joins points of equal wind speed
In the lower tropopause in the polar regions, the temperature stops lapsing earlier and the temperature is relatively warmer above the polar tropopause than above the equatorial tropopause. Above the tropopause, a warm column is over the pole and cold over the equator. This causes….
Reversal of thermal wind and creates a tendency for the wind to blow north. This northerly wind is deflected by Coriolis to the left in the southerly hemisphere resulting in and Easterly wind above the tropopause which opposes the westerly flow
High above the tropopause what winds prevail?
Easterly
What are the two main jet streams?
Subtropical jet and Polar front jet
Where is the Sub Tropical Jet found?
The altitude of around 200 HPA (FL385) at 30 degrees latitude
Where is the Polar Front Jet found?
Just below the level of the tropopause above the 500 HPA position of the polar front
In the southern hemisphere summer, the patterns move south and so the subtropical jet stream moves….
A little further south in summer and north in winter
Is the Subtropical jet stream or Polar Front Jet stream stronger?
Generally Subtropical
If the OAT drops when flying South in the Southern hemisphere where are you in relation to the jet stream?
Still below the tropopause and therefore likely to be flying under the jet stream
If the OAT rises when flying South in the Southern hemisphere where are you in relation to the jet stream?
ABove level of the tropopause and therefore likely to be flying above the jet stream
If the OAT remains the same when flying South in the Southern hemisphere where are you in relation to the jet stream?
You are likely in the jet stream core
Most common upper-level forecasts?
Route Sector Winds and Temperatures (RSWT)
GridPoint Winds and Temperatures (GPWT)
Significant Weather Prognosis (SIGWX PROG)
Where are forecasts provided in relation to RSWT?
Frequently used air routes
Levels of RDWT…
FL445 150HPA FL385 200 HPA FL340 250 HPA FL300 300 HPA FL235 400 HPA FL185 500 HPA
How is RSWT formatted?
DDSSSTT
DD- 2 numbers indicating wind direction to nearest 10 degrees
SSS- 3 numbers indicating wind speed to nearest 5kt
TT- 2 numbers indicating mean temperature in degrees Celcius without the negative sign
ISA temp also next to flight level
What is the difference between GPWT and RSWT?
GPWT forecast for the midpoint of 5x5 degree square of latitude and longitude while data in RSWT forecast refers to average weather along a particular route
What is the validity period of GPWT?
3 hours on either side of the stated validity time
What does SIGWX PROG depict?
Expected occurrence of significant weather in the airspace from FL185 to FL445
What is the validity period of SIGWX PROG?
3 hours on either side of the stated validity time
Where in the AIP can you find the approved symbols and abbreviations for SIGWX PROG?
AIP GEN 3.5/ 22
Key features of SIGWX PROG?
- Predicted location
- Level
- Maximum jet stream speed
- Height of tropopause
- Location and of expected significant weather areas above FL185
