Determination of the Total Precipitable Water by Varying the Intercept in Reitan's Relationship

Abstract

In the relationship proposed by Reitan (1963) between the total precipitable water and the dew-point temperature at ground level, the intercept is found to be a function of the scale height of the atmospheric water vapor and of the ground temperature. The scale height is closely related to the features of the vertical moisture profile in the low troposphere. The ground temperature is responsible for diurnal and seasonal variations of the intercept which are found to be of little importance. The slope coefficient is found to have a constant value of 0.068°C ?1. On this basis, a method is proposed which determines the nocturnal time pattern of the intercept, by linear interpolation in time between the daytime estimates obtained from spectral hygrometer measurements. Thus, the nocturnal time pattern of the total precipitable water can be calculated from Reitan's relationship using these interpolated values of the intercept together with the nocturnal measurements of the dew-point temperature at ground level. Satisfactory results are found by applying this method to spectral hygrometer measurements made on several days. Estimates of the total precipitable water at two stations of the Po Valley also have been obtained from Reitan's relationship by using local measurements of the dew-point temperature at ground level and suitable values of the intercept. These are determined by linear interpolation in time of the estimates of the intercept given by the radiosonde data taken from a remote station of the Po Valley. The comparison between calculated and measured values of the total precipitable water gives a satisfactory agreement for both autumn and winter periods, whereas considerable discrepancies are found on various summer days.