AbstractData from the United Kingdom operational upper air network, as well as from special radiosonde trials, have been analysed to provide statistics of spatial and temporal atmospheric variations. These statistics are applied to a study of the network performance and of representativeness errors associated with the use of the data in synoptic analysis. The results also have application to comparisons between measurements from radiosondes and those from other observing systems. For example, it is demonstrated that minimum collocation errors associated with radiosonde temperature measurements located at the centre of a satellite radiometer scan spot of radius 55 km are <1 degC for levels in the troposphere and lower stratosphere.