Magnitude of Atmospheric Pressure

• pressure at the base of a mercury column

                                          1 atm = 101.325 kPa

• water can also be used in a barometer.
• however, a much longer glass has to be used since water has a much lower density than mercury.

                                           h = 10.3 m

• meteorologists often express atmospheric pressure in another unit called bar(b)

                                           1 mb = 100 Pa

• therefore :

                                           1 atm = 1.013 b

                                                     = 1013 mb