Atmospheric Pressure Flashcards
Give the equation for Pressure
Pressure = Force/Area
What causes surface pressure?
The total weight of the column of air above you
What is the trend between static pressure and altitude
Static pressure always decreases with altitude
What instrument is used to measure pressure?
What equation explains its working?
A Mercury Barometer.
It works through atmospheric pressure acting down on the surface causes liquid mercury to rise through the tube. The height measured = pressure
P = ρgh
(Also an Android Barometer - which works alike to ASI)
What instrument do ATC use to measure pressure?
Precision Android Barometer
Works through a user increasing the pressure dial until the machine tells them that they have reached the correct pressure reading
What are isobars, and what intervals are they usually drawn at?
Isobars are lines on a surface pressure chart that join areas of equal pressure at the same level (normally MSL)
They are usually drawn at intervals of 2 or 4 hPa
What are the 3 different types of ‘iso’-lines and what are they used to show?
Isobar - Pressure
Isohypse (or Contour) - Altitude
Isotach - Speed
What happens to high/low pressure as you move further away from their respective pressure system?
High - pressure decreases away from centre
Low - pressure increases away from centre
What are “Troughs’ and ‘Ridges’ on a surface pressure chart?
Trough - Isobars pushed out by low pressure
Ridge - Isobars pushed out by high pressure
What is a Col?
An area between 2 high and 2 low pressure systems
What is the ‘Pressure gradient force’?
The net force acting on an area between the isobars
(E.g. imagine a small box between the isobars, with pressure forces acting on either side of it - the resultant force is the PGF)
Give the equation for the Pressure gradient force
Pressure gradient = Pressure difference / distance
Therefore, the closer together the isobars - the greater the pressure gradient
What is the general trend between pressure and height?
Pressure decreases with height, at a progressively decreasing rate.
This is due to less weight acting down on you, the higher you go.
The rate of decrease gets smaller since most of the weight is within the lower altitudes
As can be seen on a Contour chart - what effect does temperature have on vertical pressure variation?
In warmer air, pressure levels (shown using Isohypse) are further apart; compared to that cold air.
What are isohypse measured in?
Isohypse are measured in Decameters
