atmospheric pressure Flashcards
what is density?
the mass of a substance divided by its volume.
air pressure decreases with height will air density decrease with height?
yes
what is air density proportional to?
atmospheric pressure
where is air density greatest? (include how it decreases)
greatest nearer the earth like air pressure, the more air is compressed the greater the density.
what happens when atmospheric pressure decreases?
air expands and becomes less dense
what happens when air is heated?
expands and becomes less dense, higher the temp the less the density, lower the temp the greater the air density.
what is an isobar?
a line joining all places having the same pressure at a given level, usually sea level.
what is a low-pressure region? And what are the isobars like?
its a region of relatively low pressure shown by closed isobars, usually circular in shape with lowest pressure at center
what is a high pressure(anti cyclone) region? And what are the isobars like?
high is a region of high pressure shown by oval or circular isobars enclosing the centre of highest pressure. Isobars usually further away and slower moving.
what is a trough?
pressure system where isobars around a low becomes such that the pressure in the trough is lower than on two sides. sometimes has a sharp V shape
what is a ridge?
where isobars around an area of high pressure extends outwards, so that the pressure along the axis of ridge is higher on either side. converse of a trough except sides are usually rounder then v shaped.
what is a col?
area of almost uniform pressure between two highs and two lows.
what is a secondary depression?
a small depression within the area covered by a larger primary depression. Isobars on the side way from primary are often close together.
what is a pressure gradient?
- The force between two points: change of pressure divided by distance of pressure. Essentially the rate of increase of pressure bars (higher change of pressure over a short distance, the greater the pressure gradient).
what is the pressure lapse rate?
the fall of pressure with a gain in height. when a part of air contains warm particles, air is aid to be less dense, air molecules are far apart and column of air is tall.
what happens when a column of air contains cold particles?
air is denser, air molecules are closer together and column of air is shorter then warm counterpart.
why is rate of change of pressure greater in cold air than warm air?
a column of cold air weighs more than a column of warm that’s why.
what is the average pressure lapse rate in lower atmospheres?
1hPa per 27ft(round up to 30ft)
what does ISA stand for
International standard atmosphere
what is the average sea level atmospheric pressure?
1013.2hPa
what is the average sea level temperature
15 degrees
what is the standard temperature lapse rate?
1.98(2) degrees per 1000ft
what does QRB stand for?
what’s your distance?
what does QRC stand for?
whats your true bearing?
what does QFF stand for?
pressure at sea level
what does QFE stand for?
pressure at particular airfield observation station(Field elevation)
what does QFH stand for?
current mean sea level pressure
what does QFE represent?
the weight of column of air above airfield.
how do you calculate QFE?
stimated with rule of thumb of pressure lapse rate . divide known airfield elevation by 30. Using ISA pressure of 1013 hPa at sea leave, minus the answer from it and set on altimeter.
what does QNH stand for?
altitute at sea level
what is the normal altimeter setting?
QNH
what happens if you fail to adjust the altimeter
failing to adjusting QNH when flying from areas of high pressures to low, altimeter will indicate a constant altitude. However aircraft actual altitude above sea level will be lower then indicated.
what does the mnemonic Hi-Lo-Hi represent?
flying from high pressure to low it will read high. Therefore your lower then indicated on altimeter
what does the mneomonic Lo-Hi-Lo represent?
flying from low pressure to high it will read low therefore you’re higher then indicated on altimeter
