The Bowen Ratio is defined as the ratio between the sensible heat $Q_h$ and the latent heat $Q_e$:
$$R= Q_h/Q_e=0.00061*p* \frac {T_s-T_a} {e_s-e_a} $$
where $T_s$ is the temperature of the water surface and $T_a$ is the temperature of the atmosphere in degrees Celsius. while $e_s$ are the vapour pressure of the water surface and $e_a$ of the atmosphere, $p$ is the atmospheric pressure in mb (millibar). The Bowen ratio is used among other applications for the energy budet of open lake evaporation.