Variability in the mesosphere observed by the Nimbus 6 pressure modulator radiometer

Abstract

The pressure modulator radiometer flew aboard Nimbus 6, collecting radiance data from June 1975 until June 1978. These data have been processed to yield daily temperatures, geopotential heights, and balance wind estimates from the stratosphere and mesosphere (30–85 km) for the entire period. We use these data to examine the variability of both the zonal‐mean and the nonzonal disturbances present in the data. In terms of the zonal‐mean, we show that the COSPAR International Reference Atmosphere (1986), developed from these data, can be misleading in the mesosphere due to the underlying interannual variability and the merging with other data sets. Daily variability of the zonal‐mean flow is examined, and these data show strong evidence of coupling between the stratosphere and mesosphere for such variations. We also find evidence for significant coupling of wave‐like events in the stratosphere and the mesosphere but that not all such disturbances seen in the mesosphere are due to simple propagation from below. Space‐time spectral analysis is used to search for traveling planetary waves: Results show a weak 5‐day normal mode present in the Equinox seasons, which appears to correspond to the first symmetric mode predicted by theory. These data also show clear evidence of the 4‐day wave in all three southern winters examined and are consistent with the hypothesis that this mode grows due to instability of the background zonal flow.