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Measuring weather
Surface observations - pressure
Pressure is a "push" force that, in the atmosphere, is the result of many molecules bouncing off one another and other surfaces, like the ground. The more molecules pushing on something, the greater the pressure. When measuring atmospheric pressure near the ground, we measure the net effect of all air molecules directly overhead a given area. Because of this, surface pressure is essentially the weight of the air above expressed as the force per unit area (Newtons per square meter, or a "pascal", Pa). Atmospheric pressure measured near the surface is roughly 101300 Pa, but rather than using large pascal values or units more common in the United States, like psi or inches of Mercury, meteorologists tend to use hectopascals (hPa) which is the same as the millibar (mb). So atmospheric sea level pressure would commonly be recorded as 1013 hPa which is the same as 1013 mb.
Since air is compressible, becoming denser as it is squeezed, gravity holds a
greater amount of air close to the ground. Therefore, when atmospheric pressure
is measured at higher and higher altitudes, like at the top of a mountain, not
only is there less air overhead compared to a measurement at sea level, there is
MUCH less air overhead, exponentially less, as you can see in the graph
to the right.
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in situ, surface observations, pressure
Links and resources
Surface observations - pressure
Pressure is a "push" force that, in the atmosphere, is the result of many molecules bouncing off one another and other surfaces, like the ground. The more molecules pushing on something, the greater the pressure. When measuring atmospheric pressure near the ground, we measure the net effect of all air molecules directly overhead a given area. Because of this, surface pressure is essentially the weight of the air above expressed as the force per unit area (Newtons per square meter, or a "pascal", Pa). Atmospheric pressure measured near the surface is roughly 101300 Pa, but rather than using large pascal values or units more common in the United States, like psi or inches of Mercury, meteorologists tend to use hectopascals (hPa) which is the same as the millibar (mb). So atmospheric sea level pressure would commonly be recorded as 1013 hPa which is the same as 1013 mb.
Since air is compressible, becoming denser as it is squeezed, gravity holds a
greater amount of air close to the ground. Therefore, when atmospheric pressure
is measured at higher and higher altitudes, like at the top of a mountain, not
only is there less air overhead compared to a measurement at sea level, there is
MUCH less air overhead, exponentially less, as you can see in the graph
to the right.
Next page
->
in situ, surface observations, pressureLinks and resources
