Estimating mean weighted temperature of the atmosphere for Global Positioning System applications

A water‐vapor‐weighted vertically averaged mean temperature of the atmosphere, T m , is a key parameter in the retrieval of total water content from the measurements of Global Positioning System signal delays. The accuracy of precipitable water estimates is proportional to the accuracy of T m . The geographic and seasonal variability of T m based on 23 years of radiosonde soundings at 53 globally distributed stations is presented. Several methods for estimating T m were evaluated by comparing the estimates against the actual T m values. Sitespecific climatology or site‐specific linear regression was superior to the geographically and seasonally invariant regression relationship typically used to estimate T m . Relative errors at most stations were less than 2%, which corresponds to absolute errors of precipitable water of 0.1–0.5 mm The station‐specific linear regression was superior to climatological means as an estimator except in the tropics, where correlations between T m and T sfc were not high. Also, a physical model was developed to indicate the relationship between T m and other commonly used atmospheric variables.