Flashcards in Upper Level Meteorology Deck (51)
What happens to atmospheric pressure as there is an increase in altitude?
What is the ISA atmospheric pressure?
1012.25 HPA at mean sea level
What is the atmospheric pressure at each altitude?
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
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
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
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?
Max jet stream speed?
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