5: Atmospheric Pressure
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Fundamental Principle: Force 1) Define 2) Vector quantity of 3) Formula 4) SI Units
1) strength or energy as an attribute of physical action or movement 2) magnitude & direction 3) Force = mass x acceleration (gravity) 4) 1 Newton (N) = 1 kg m s-2
Fundamental Principle: Pressure (Pa) 1) Define 2) Formula 3) SI Units 4) High force = 5) Large area =
1) Force acting per unit of area 2) Pressure = force / area 3) 1 kg m s-2 / m2 = 1 kg m-1 s-2 4) High pressure 5) Low pressure
Does pressure increase or decrease with height?
Decreases
Fundamental Principle: Density (p) 1) Define 2) Formula 3) SI Units 4) Which is the more denser state, gas or solid?
1) Degree of compactness of a substance 2) Mass / volume 3) kg m-3 4) Solid
Atmospheric pressure acts
Acts equally in all directions at any one given point
Hydrostatic Equation 1) Define 2) Formula What each part of the formula means 3) Delta P 4) p 5) Delta z 6) g
1) Relates a change in pressure to a change in height 2) ^P = -p x ^z x g 3) Change in pressure (Pa) 4) Density 5) Change in height (m) 6) Gravity
1) Which is denser, cold or warm air? 2) and why?
1) Cold air 2) Pressure decreases more rapidly with height in cold air
Where does the hydrostatic equation work? Where does it not work?
1) When there is no net vertical motion (synoptic scale) 2) Strong vertical motions. Scales < 10 km (thunderstorms, up/down drafts)
Which pressure gradients are larger, Vertical or horizontal?
Vertical pressure gradients
Why dont we feel the large vertical pressure gradients?
Gravity counteracts the vertical pressure gradient
Measuring pressure - Mercury Barometer (1 Atm) 1) Does high pressure cause the height of mercury to increase or decrease? 2) Does volume of mercury change temperature 3) 1 atm = ? hg = ? hPa = ? m
1) Increase, while lower pressure causes it to decrease 2) Yes 3) 760 mm Hg = 1013 hPa = 10.33 m H2O
Measuring pressure - Verner Scale 1) how to work it
Find the first green increment that connects to the blue increment and measure in mm
Pressure Units 1) 1 hPa = ? Pa = ? mb 2) 1 kPa = ? Pa = ? hPa 3) What are meteorological measurements in? 4) Average sea level pressure
1) = 100 Pa = 1 mb 2) = 1000 Pa = 10 hPa 3) hPa 4) ~ 1013 hPa
1) Rising barometer readings = a) which means? 2) Lower barometer readings = b) which means?
1) High pressure a) Generally clear-sky conditions 2) Low pressure b) Generally stormy & cloudy weather
1) Why cant pressure at different locations be directly compared? 2) What do we use to overcome this?
1) They are at different sea levels 2) The hydrostatic equation to reduce them to se level
Reduction to sea level pressure Question: Height of sea level = 300m Pressure = 950 hPa Density = 1.3 kg m -3
^P = -p x ^z x g ^P = -1.3 kg m -3 x 300 m x 9.81 m s --2 = - 3825.9 kg m-1 s-2 = - 3825.9 Pa (Negative due to pressure decreases with height) = 95000 Pa + 3825.9 Pa = 98825.9 Pa = 988.259 hPa
What does MSLP stand for?
Mean Sea Level Pressure