Accuracy of humidity measurements on ships: Consideration of solar radiation effects

The effect of heating due to solar radiation on measurements of humidity obtained from ships is examined. Variations in wet- and dry-bulb temperature measured on each side of a research ship are shown to correlate with solar radiation. However, the resulting variations in the measured humidity are shown to be negligible (less than 0.1 g kg−1). Any radiation induced humidity errors in data from merchant ships participating in the Voluntary Observing Ship Special Observing Programme for the North Atlantic are also shown to be small, less than 0.2 g kg−1. For calculation of the latent heat flux, the near-surface humidity should be calculated from the observed wet- and dry-bulb temperatures, whereas the dry-bulb temperature should be corrected for radiation-induced errors before calculation of the atmospheric stability or the sensible heat flux.