Annual and semiannual waves in the temperature of the mesosphere as deduced from Nimbus 6 PMR measurements

The annual and semiannual waves in zonal mean temperature in the mesosphere are analysed using data from the Nimbus 6 pressure modulator radiometer (PMR). The observation that the annual temperature cycle in the extratropical upper mesosphere has almost exactly opposite phase to the solar cycle and explains over 90% of the total variance suggests that the mechanism which maintains the temperature structure is very closely linked with the annual solar cycle. The occurrence of a peak in the semiannual oscillation around 64° latitude in the southern hemisphere contrasts with an amplitude maximum nearer to the pole in the northern hemisphere, reflecting the different characteristics of sudden warmings between the hemispheres which are the cause of this wave. In the upper mesosphere the semiannual wave has similar phase at all latitudes. This gives rise to a pronounced semiannual wave in the global mean temperature of the upper mesosphere.