205W Atmospheric Pressure

Define atmospheric pressure.

Force per unit area exerted by the atmosphere as a consequence of its weight

Define station elevation

The vertical distance in meters above Mean Sea Level of the datum level to which barometer readings are corrected to give station pressure

Define mean sea level

Computed from the station pressure and reported in observations so that the barometric pressure at stations of different elevations can be compared

Define the ICAO standard atmosphere

Air is a perfectly dry gas
Sea level pressure is 29.92 Hg or 1013.2 hPa
Temperature at sea level is 15 degrees Celsius
Temperature decreases at a rate of 1.98 degrees celsius / 1000ft

What is the unit used for pressure

hectopascal

If HWOS is not working where would you obtain pressure data?

From a digital barometer

What is the requirement for adding the remark PRESRR

The pressure is increasing by 2.0 hPa an hour

What is the requirement for adding the remark PRESFR

The pressure is decreasing by 2.0 hPa an hour

Define pressure tendancy

The characteristic and the amount of change in station pressure during the three hours preceding the observation

Which reports shall include the pressure tendency?

0000, 0300, 0600, 0900, 1200, 1500, 1800, 2100

When the pressure tendency trace resembles two codes, which code should it be categorized as?

The one that most resembles the last portion of the trace

Which codes are normally used if a trace resembles three codes?

2 or 7