Here T i {\displaystyle T_{\text{i}}} and p i {\displaystyle p_{\text{i}}} are the absolute temperature and pressure at the beginning of the process (here equal to the ambient air temperature and pressure), T f {\displaystyle T_{\text{f}}} and p f {\displaystyle p_{\text{f}}} are the absolute temperature and pressure in the vortex core (which is the end result of the process), and the constant γ {\displaystyle \gamma } is about 7/5 = 1.4 for air (see here).