Comments on “On the Estimation of Overwater Bowen Ratio from Sea–Air Temperature Difference”*

Abstract

The Bowen ratio is an important parameter in the study of air‐sea interaction, particularly in the study of moisture convergence. It is the ratio of sensible to latent heat exchange. Recently, Hsu (1998) reported an interesting relationship between the sea‐air temperature difference (Ts 2 Ta) and the overwater Bowen ratio (B), based on thermodynamic considerations. He used the data collected at four stations in the Gulf of Mexico during the period 1993‐97 and proposed a generic relationship of the form b B 5 a(T 2 T ) sa (1) where the values of a and b are estimated from the field experiments. For open sea conditions, the value of a varied from 0.077 to 0.078, b from 0.67 to 0.71, and the correlation coefficient (r) from 0.85 to 0.89. Very similar results were found in a nearshore region (for Grand Isle, Louisiana). The equation with the highest correlation coefficient (r 5 0.85) is given by Hsu (1998) as 0.69 B 5 0.077(T 2 T ). sa (2) Normally, values of B are large for cold air outbreak conditions. Chou and Yeh (1986) observed B to vary between 0.61 and 0.78 over midlatitude coastal water during cold air outbreak events. During Air-Mass Transportation Experiment (14‐28 February 1974), the value of B was about 0.8 over the Yellow Sea. Hsu also reported Bowen ratios that were substantially higher during a cold-air outbreak that resulted in enhanced sensible heat flux over latent heat flux under these conditions. The linear regression given by Hsu (1998) is 0.81 B 5 0.097(T 2 T ). sa (3)