Validation of temperature retrievals obtained by the Limb Infrared Monitor of the Stratosphere (LIMS) Experiment on NIMBUS 7

The LIMS is a six‐channel limb scanning infrared radiometer flying on the NIMBUS 7 spacecraft. It measured radiances from October 25, 1978 to May 28, 1979, from which vertical profiles of temperature, ozone, water vapor, nitric acid and nitrogen dioxide were derived. The temperature is of major importance for studies of middle atmospheric dynamics, as well as for chemical and radiative studies. It is also needed by LIMS in order to derive the concentrations of the trace gases. This paper briefly outlines the temperature determination (as a function of pressure) from measurements in two channels covering portions of the 15‐μm band of CO 2 . The known sources of error, from the radiometer and data reduction, are used to estimate the systematic and random errors (accuracy and precision, respectively) expected of the results. Observational determinations of the complete end‐to‐end precision are obtained by computing the standard deviation of six sequential temperature retrievals in regions where the atmosphere is horizontally uniform. This yields values of 0.2 to 0.6 K, in reasonable agreement with the estimates. A correction for horizontal gradients in the atmosphere leads to a large reduction in the differences between the stratospheric temperatures determined on the ascending and descending portions of the orbit. The temperatures agree in the mean with radiosondes and rocketsondes to within 1–2 K in most regions below 1 mbar. This is approximately the accuracy of these in situ sensors in the stratosphere. Above 1 mbar, LIMS temperatures are cooler than rocketsondes by a few degrees at all latitudes, especially in mid‐latitude winter. However, comparisons with other results suggest that rocket temperatures are high, contributing at least part of the error. The temperature cross sections show several interesting features, such as cold regions in the mid‐latitude mesosphere and wavelike vertical variations in the tropics, which have not been seen before. These data provide a useful and in some ways unique basis for studies of the stratosphere and mesosphere.