What is air pressure?
The air in the atmosphere exerts a pressure directed towards the Earth’s surface, caused by gravity. This is the atmospheric pressure.
Air pressure is measured in hectopascals (=100 Pascal), abbreviated hPa. In the past, millibars (mbar) or torr (mm Hg) were also common. 1 hPa corresponds to 1 mbar or around 0.75 mm Hg.
The air pressure depends heavily on the thickness of the air column above the measuring point. This means that the air pressure is highly dependent on altitude. While in water the pressure decreases linearly with increasing altitude, in air it decreases exponentially. This is because the higher layers of air exert pressure on the layers of air below, which compresses them. The altitude dependence of the air pressure is particularly high at altitudes close to sea level. Here the air pressure decreases by 1 hPa for every 8 m increase in altitude. At around 5500 meters the pressure then decreases by about 1 hPa for every 15 m increase in altitude.
Air pressure decrease with altitude according to the standard atmosphere (ISA). At an altitude of 5500 meters, the air pressure has decreased by half.
Air pressure decreases with altitude according to the standard atmosphere (ISA). At an altitude of 5500 meters, the air pressure has decreased by half. (MeteoSwiss)
Reduce air pressure at sea level
In order to be able to compare the air pressure measured at russia phone number library different locations, the influence of the altitude of the measuring location must be excluded; the pressure must be “reduced” to sea level. The reduced air pressure indicates the value that would be measured if the measuring station were at sea level. Only after this correction can air pressure values measured at different altitudes be compared.
This reduction can be done in different ways:
QFF : Reduced air pressure at sea level depending on the current temperature. This value is shown, for example, on weather maps.
QNH : Air pressure reduced to sea level, using the standard atmosphere used in aviation. This value is used in aviation.
The effective air pressure measured at a measuring station without altitude reduction is called QFE .
When do we speak of a high?
But when do we speak of high air pressure, or of a high? The average air pressure over the years (reduced to sea level, QFF) is around 1018 hPa. So you could say that values above this probably correspond to high pressure, and those below this to low pressure. But that doesn’t always have to be true. The relative distribution of air pressure is much more important than the absolute pressure value. To do this, the pressure distribution in a larger area must be considered. Where the highest what is content marketing? and why is it important? pressure is measured, we speak of a high pressure area – regardless of the absolute values. This can sometimes be as high as 1015 hPa. Typical values for a high pressure area in winter are around 1034 hPa, or around 1023 hPa in summer.
The highest values of air pressure reduced to sea level (QFF) measured over Switzerland are around 1048 hPa. The absolute record for the highest air pressure worldwide is 1084.8 hPa, measured on 19 December 2001 in Tosontsengel in Mongolia. As this value comes from an altitude of 1725 m above sea level and thus a large correction was necessary when reducing to sea level, the WMO maintains another record that is limited to measurements at altitudes below 750 m above sea level. germany cell number And here the record is 1083.3 hPa, measured on 31 December 1968 in Agata, Siberia.
Pressure distribution on Sunday, February 5th at 1pm. Over Great Britain the air pressure values are above 1045 hPa.