Pressure

Question 1

Diurnal pressure variation

Answer 1

Max pressure drop occurs at 1600 it then increases peaking around 2200, it then decreases and bottoms around 0400 and a second peak occurs around 1000

Question 2

Density effect of pressure increase

Answer 2

Density increase

Question 3

Density effect of temp increase

Answer 3

Density decreases

Question 4

Density effect of altitude increase

Answer 4

Density decrease

Question 5

Density effect of water vapour increase

Answer 5

Density decrease

Question 6

Density altitude

Answer 6

Reflects the influence of temperature on pressure altitude, it’s the best measure of aerodynamic and engine performance. It changes at 120ft/1°C

Question 7

How to work out density altitude

Answer 7

1. Find the difference between the actual temp and the ISA temp at the altitude
2. Apply the correction of 120ft/1°C
3. Add this correction to the pressure alt if is actual temp is above ISA and vice versa

Question 8

Effect of diurnal pressure variation in mid-high attitudes

Answer 8

Has little significance due to weather systems, pressure has the biggest effect in equatorial regions so diurnal pressure variation is more pronounced there

Question 9

How to work out pressure alt

Answer 9

((1013 - QNH) x 30) + elevation

Question 10

Lee troughs

Answer 10

Non-frontal low associated with mountainous terrain, caused as the air builds up on the windward side of the mountain leaving an area of low pressure on the lee side. The depression is only located at low level and conditions are similar to Fohn wind

Question 11

Thermal/heat lows

Answer 11

Owing mainly to the distribution of land and sea the surface layers are subject to unequal heating and there is a tendency for warmer regions to be areas of low pressure

Question 12

Localised pressure changes associated with TS

Answer 12

Pressure changes quite a lot over a small distance in the VC of TS, this is because some of the falling rain evaporates cooling the air and making it heavier. Where the rain is falling pressure goes up by a few hPa. Also as air rises in the TS updraft, it creates an area of low pressure under the updraft that acts to pull air in from around the TS which is also usually a few hPa’s lower than the general area. At the top of the storm the pressure is higher compared to areas away from the storm