meterolgy ( chapter 3 > required skills and knowledge )

units for atmospheric pressure

1. Hectopascals ~ 1013.25 how

2. Inches of mercury 29.92 Hg

Mercury barometer

1. Senses variations in atmospheric pressure, which in turn will either decrease or increase the height of the mercury height of mercury

2. High atmospheric pressure downwards ~ mercury level increase ( height increases )

Aneroid barometers

1. Use a small, evacuated, flexible metal chamber / capsule with a spring inside

2. Small changes in external air pressure cause the capsule to expand or contact

Isobars

1. Are lines of equal pressure on a pressure map

2. They are drawn as long continuous black line

3. Usually given a value in even numbers

A high pressure ( high anticyclone )

Is a region where the atmospheric pressure at the surface is greater than its environment

A ridge is

An extension of high, characterised by protrusion of isobars away from the centre of high

A low pressure

Is an area in which atomooheric pressure is less than its surroundings. A trough is it extension

Pressure ? With height

Decreases

QNE is …

The reading on the altimeter on the ground when it is set to 1013.25 hpa

QNH is

QFE adjusted / corrected to mean sea level using the ISA temperature lapse rate

QFF is

Corrected / adjusted to mean sea level using the weather or forecast

QFE is

The pressure at the aerodrome reference point

ISA conditions, pressure is approximately

1. 50% of MSL at 18,000ft and

ISA conditions, density is approximately

1. 50% MSL at 22,000 ft

2. 25% MSL at 40,000 ft

The closer the isobars spacing …

The greater the pressure gradient force and therefore faster windspeed

Horizontal pressure gradient is directed …

From High pressure to low pressure

The horizontal pressure gradient

Is a pressure vector resulting from the difference in pressure along the horizontal plane