1. The arbitrarily selected atmospheric pressure of 1000 millibars to which adiabatic processes are referred for definitions of potential temperature, equivalent potential temperature, etc. 2. A pressure of 1 atmosphere (101.325 Newtons per square meter), to which measurements of quantities dependent on pressure, such as the volume of a gas, are often referred. Also known as "normal pressure."

a convenient measure of pressure equivalent to 1 atmosphere or 1.01×105 pascal.

a unit of pressure: the pressure that will support a column of mercury 760 mm high at sea level and 0 degrees centigrade

Pressures 1 bar

The same as standard atmosphere; equal to a pressure of 14.696 pounds per square inch.

(P° or P) Standard pressure is a pressure of 1 bar. Before 1982, the standard pressure was 1 atm (1 atm = 1.01325 bar).

1. A pressure of one atmosphere, in SI units, 101 325 N m−2. In older works standard pressure sometimes means the arbitrary reference pressure in the expression for potential temperature; but this use of standard pressure should be avoided, given the widespread use of standard pressure in many fields of science to mean a pressure of one atmosphere. Compare standard temperature. In meteorology, the arbitrarily selected atmospheric pressure of 1000 mb to which adiabatic processes are referred for definitions of potential temperature, equivalent potential temperature, etc. Other pressures may be used as standard for specific purposes.