2- Pressure Flashcards
What helps us measure the height of aircraft above a surface?
the vertical variation of pressure
What measures the vertical variation of pressure?
the Altimeter
What is atmospheric pressure?
air is made up of molecules, air therefore has mass, and under the force of gravity, exerts a pressure on the earth’s surface.
Put simply: the pressure of the atmosphere at any point is caused by the weight of the column of air above that point.
Where is most of the atmosphere located?
Why?
most of the mass of the atmosphere is contained in the lower layers near the earth’s surface.
Because the force of gravity is greater nearer the centre of the earth
Because the force of gravity is greater nearer the centre of the earth, most of the mass of the atmosphere is contained in the lower layers near the earth’s surface.
What then can we say about air density and pressure?
air is denser and pressure is greater at the surface than at altitude
How pressure is represented and measured in meteorology:
- Millibars (mb) «_space;still used in exams
- Hectopascals (hPa) «_space;standard unit used
2 types of instruments used to measure atmospheric pressure:
- Aneroid Barometer (non-liquid)
- Mercury Barometer
How does an Aneroid Barometer work?
Measures the effect of air pressure on a metal chamber from which part of the air has been removed. Changes in air pressure make the chamber expand or contract, which moves a needle around a dial.
What is one downside and one positive about an Aneroid Barometer?
less accurate than a mercury barometer but more sensitive
How does a Mercury Barometer work?
changes in the atmospheric pressure (changes in the force or weight of the atmosphere), will either depress the mercury from the open reservoir to the top of the tube (high pressure) or the other way round
What unit is used to measure displacement?
inches
What is the average height of a column of mercury that can be supported by the atmospheric pressure at MSL?
29.92 inches = 1013.92 mb or hPa
Why might we get a high pressure in one area and a low pressure in another?
It depends on the amount of air over an area, if one day a place has more air over the surface, then the weight of air will increase and the pressure of air will increase. This gives rise to horizontal surface pressure variations, more commonly known as high and low pressures.
In weather charts, what are the lines called?
how do they work?
Isobars
the lines are called Isobars and they connect points of equal pressure.
How can we know how strong the Pressure Gradient Force is?
closely spaced isobars show a large change in the pressure therefor a large PGF. That is common within low pressures. the opposite is common within high pressures.
