Variations of Pressure

Height 

With an increase in height, the weight of air overlying the surface will reduce. Therefore pressure will fall with height. The rate of change of pressure with height (the barometric lapse rate) reduces as altitude increase or the height change per hPa increases as altitude increases 

However, the temperature has a dramatic effect on the pressure change with height, i.e. the pressure lapse rate. Warm air will cause pressure to fall slowly with height, i.e. decreasing the pressure lapse rate, whereas cold air will cause pressure to fall rapidly with height, i.e. increasing the pressure lapse rate. Therefore we would expect the pressure at any given height to be higher over warm air and lower over cold air. The effect of temperature on the rate of change of pressure with height is an important fact which we will return to in altimetry and upper winds. 

Shown below is how temperature affects the height difference with a 1 hPa change in pressure. These values have been derived from the formula described in the chapter on the atmosphere. 

There is a change in pressure during the day which although small (about 1 hPa in temperate latitudes, can be as much as 3 hPa in the tropics) would need to be taken into account when considering pressure tendency as an indication of changing the weather. The variation is shown below. 

Diurnal Variation 

There is a change in pressure during the day which although small (about 1 hPa in temperate latitudes, can be as much as 3 hPa in the tropics) would need to be taken into account when considering pressure tendency as an indication of changing the weather. The variation is shown below. 


Diurnal Variation 

The variation is difficult to explain but is probably due to a natural oscillation of the atmosphere having a period of about 12 hours, this oscillation being maintained by the 24-hour variation of temperature.

error: Content is protected !!