Estimation of Errors in Nimbus 6 Temperature Profiles and Their Spatial Correlation

Abstract

Using an 8-day series (18?26 August 1975) of multivariate statistical analyses of European radiosonde data together with a measure of analysis error, we have estimated error statistics from 959 Nimbus 6 temperature profiles for 10 isobaric layers in the troposphere and lower stratosphere. The mean error or bias is largest near the tropopause (+0.9°C) but changes sign several times in the vertical so that the integrated mean error for the atmospheric column 1000?70 mb is small (?0.1°C). The root-mean-square error peaks at the tropopause (2.9°C) with a minimum in the midtroposphere (1.0°C). In all layers, the horizontal correlation of retrieval error shows little systematic dependence on direction but strong dependence on distance. The correlation is greater than 0.50 at distances less than 400 km and less than 0.10 at 800 km and beyond, and it can be approximated by a Gaussian curve. The vertical correlations are greatest between adjacent layers (?0.50); negative correlations exist between layers on opposite sides of the tropopause. This information is useful in any statistical objective analysis which accounts for observational error.