Abstract
Reliable measurements of evaporation are of importance in many scientific fields.
In the worldwide routine meteorological observation the evaporation rate per day is frequently measured by the evaporimeter pan.
The amount of evaporation can be roughly obtained by measuring water depth in the pan and this has been done by a hook gauge up to the present. In this method the wind often influences the measurement, and a small amount of evaporation for short periods of time could not be measured.
Recently, accuracy in measuring salinity was improved by use of an electric conductivity technique and it has become possible to measure salinity within an accuracy of ±0.003‰. Then, even a trace amount of evaporation during a short time interval can be detected by measuring salinity change in the salt water pan.
The relative error is kept under about 2.5% by this method.
The sampling error of salinity was estimated not more than 4×10-4‰ and the fallout of salt particles near the seashore was about 3.6×10-5‰.
The amount of evaporation from two salt water pans of the same type showed a good agreement. Moreover, the difference between the amounts of evaporation from the salt water pan and the fresh water pan is not appreciable for long periods of time. However, the amount of evaporation from fresh water is apt to become larger as the observation time interval is shortened. It was found that the amount of evaporation from the salt water pan had a linear relationship to the vertical vapor fluxes estimated by the bulk method. The proportional coefficient of vapor fluxes to the amounts of evaporation from the pan was about 0.67. It is a temporary value and should be determined from further experiments at various places and in various atmospheric conditions in future.
