Observations of the 5–Day Wave in the Stratosphere and Mesosphere

Abstract

Observations from the Nimbus?6 Pressure Modulator Radiometer (PMR) are presented showing evidence of a westward traveling wave of period 5 to 6 days. The wave is observed throughout the 20 month time span of the dataset. The amplitude ranges from 0.5 K at 45 km altitude to about 1.0 K at 85 km. The horizontal structure resembles that of the gravest symmetric wavenumber 1 free Rossby wave and the vertical structure is similar to that of a Lamb wave. There is no evidence of a vertically trapped wave in the summer mesosphere, although some asymmetry is noticeable. The PMR data have been supplemented by using data from the Nimbus- 5 Selective Chopper Radiometer (SCR) to investigate vertical structure and seasonal modulation of wave period. The results show that the wave amplitude grows with height but decreases at 62 km. The period is closer to 6 days in the spring and autumn and about 5.2 days in winter and summer.