Exner function

The Exner function is an important parameter in atmospheric modeling. The Exner function can be viewed as non-dimensionalized pressure and can be defined as:
 * $$\Pi = \left( \frac{p}{p_0} \right)^{R_d/c_p} = \frac{T}{\theta} $$

where $$p_0$$ is a standard reference surface pressure, usually taken as 1000 hPa; $$R_d$$ is the gas constant for dry air; $$c_p$$ is the heat capacity of dry air at constant pressure; $$T$$ is the absolute temperature; and $$\theta$$ is the potential temperature.