5: Atmospheric Pressure

Question 1

Fundamental Principle: Force

1) Define
2) Vector quantity of
3) Formula
4) SI Units

Answer 1

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

Question 2

Fundamental Principle: Pressure (Pa)

1) Define
2) Formula
3) SI Units
4) High force =
5) Large area =

Answer 2

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

Question 3

Does pressure increase or decrease with height?

Answer 3

Decreases

Question 4

Fundamental Principle: Density (p)

1) Define
2) Formula
3) SI Units
4) Which is the more denser state, gas or solid?

Answer 4

1) Degree of compactness of a substance
2) Mass / volume
3) kg m-3
4) Solid

Question 5

Atmospheric pressure acts

Answer 5

Acts equally in all directions at any one given point

Question 6

Hydrostatic Equation
1) Define
2) Formula
What each part of the formula means
3) Delta P
4) p
5) Delta z
6) g

Answer 6

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

Question 7

1) Which is denser, cold or warm air?

2) and why?

Answer 7

1) Cold air

2) Pressure decreases more rapidly with height in cold air

Question 8

Where does the hydrostatic equation work?

Where does it not work?

Answer 8

1) When there is no net vertical motion (synoptic scale)

2) Strong vertical motions. Scales < 10 km (thunderstorms, up/down drafts)

Question 9

Which pressure gradients are larger, Vertical or horizontal?

Answer 9

Vertical pressure gradients

Question 10

Why dont we feel the large vertical pressure gradients?

Answer 10

Gravity counteracts the vertical pressure gradient

Question 11

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

Answer 11

1) Increase, while lower pressure causes it to decrease
2) Yes
3) 760 mm Hg = 1013 hPa = 10.33 m H2O

Question 12

Measuring pressure - Verner Scale

1) how to work it

Answer 12

Find the first green increment that connects to the blue increment and measure in mm

Question 13

Pressure Units

1) 1 hPa = ? Pa = ? mb
2) 1 kPa = ? Pa = ? hPa
3) What are meteorological measurements in?
4) Average sea level pressure

Answer 13

1) = 100 Pa = 1 mb
2) = 1000 Pa = 10 hPa
3) hPa
4) ~ 1013 hPa

Question 14

1) Rising barometer readings =
a) which means?
2) Lower barometer readings =
b) which means?

Answer 14

1) High pressure
a) Generally clear-sky conditions
2) Low pressure
b) Generally stormy & cloudy weather

Question 15

1) Why cant pressure at different locations be directly compared?
2) What do we use to overcome this?

Answer 15

1) They are at different sea levels

2) The hydrostatic equation to reduce them to se level

Question 16

Reduction to sea level pressure
Question:
Height of sea level = 300m
Pressure = 950 hPa
Density = 1.3 kg m -3

Answer 16

^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

Question 17

What does MSLP stand for?

Answer 17

Mean Sea Level Pressure