Temperature, Pressure Changing Rates in Air Masses
Name: Marcel T.
Date: Summer 2012
As an air mass rises in the atmosphere does the pressure change faster in warm or cold air?
In cold air, because it is denser at the same pressure. Pressure within an unconstrained fluid is from the weight of fluid above it. In cold air, weight and thus pressure decreases more quickly with increasing altitude.
Richard E. Barrans Jr., Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
It is difficult to make a generalization. Consider the ideal gas law: PV = nRT --> d = (n/V) = P/RT where “d” is the molar density. So the lower the density the faster the air will rise. However, the density is proportional to “P” and inversely proportional to “T” (using consistent sets of units). But “P” and “T” can change independently. So it is the ratio of P/T that determines the density.
As an air parcel rises, it cools as it expands, as it is rising into
cooler air. The faster the decrease in temperature with height, the
more quickly the parcel expands. The pressure in the parcel decreases
as it rises into decreased atmospheric pressure with height.
So, the temperature of the air surrounding the parcel, whether warmer
or colder, is not the determining factor. The most important factors
are the rates of decrease of pressure and temperature with height. The
faster the parcel rises, due to the extent of decreasing pressure and
temperature above it, the faster the pressure in the parcel will decrease.
David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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Update: November 2011