The relationship between total precipitable water and surface-level humidity over the sea surface: A further evaluation

The fifth-order polynomial regression relating total precipitable water (W) and surface-level humidity (Q) over the sea surface, proposed by Liu (1986), has been further verified by instantaneous radiosonde ascents from 13 experiments conducted in geographically different regions ranging from the equatorial Pacific to the Norwegian Sea. When Q ranges from 3 to 21 g/kg, the composite root-mean-square-error between Liu's formula and these 13 experiments is found to be approximately 1 g/kg. It is therefore suggested that as a first approximation, Liu's formula may be useful for operational weather analysis and forecasting using instantaneous data, inasmuch as Q can be determined with W measured routinely worldwide by satellites.