Chapter 3 - Atmospheric pressure Flashcards
What is atmospheric pressure?
It is the static pressure caused by the weight of the air above the measurement point. It is measured of the force per unit area
What are the two principle units of measure of atmospheric pressure?
They are hectopascals and inches of mercury
1013.25 hpa = 29.92 inHg
What do Mercury barometers sense?
It senses variations in atmospheric pressure, increasing or decreasing the height of a column of mercury within an evacuated tube
How do Aneroid barometers work?
They use small, evacuated, flexible material chamber/capsule with a spring inside; small changes in external air pressure cause the capsule to expand or contract
What are isobars?
They are lines of equal (constant) pressure on a pressure map. Get are drawn as a long, continuous black line and are usually given a value in even numbers
What is a high-pressure, high (anticyclone)?
It is a region where the atmospheric pressure at the surface is greater than its surrounds environment
What is a ridge?
It is an extension of a high, characterised by a protrusion of isobars away from the centre of the high
What is a low-pressure?
It is an area in which the atmospheric pressure is less than its surroundings. A through is its extension
What is the pressure laps rate approx. at 30ft?
30ft per hPa at mean sea level
What is QFF?
It is the barometric pressure at the observation point, reduced to MSL using observed temperature at the surface and assuming pressure change consistely with change in temperature
What is surface wind?
It is the wind blowing 10 m (33ft) agl in in an area where the distance between the instrument and any obstruction is at least 10 times the height of the obstruction
Near the Earth’s surface, the horizontal pressure gradient creates a…?
Pressure gradient force, which is directed from higher to lower pressure
If the isobars are close in spacing, what does it mean?
It means that there is a greater pressure gradient force and therefore the fast the windspeed
