This study investigates contributions of planetary waves (PWs) to the mean flow in the middle atmosphere during the Northern Hemisphere winter when PW activities are strong, by analyzing satellite data from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). It is suggested that there would be opposite contributions between easterly acceleration by monthly mean stationary planetary waves (STPWs) and westerly acceleration by remaining traveling planetary waves (TRPWs) in the high-latitude lower mesosphere. When easterly winds appear in the mesosphere, STPWs propagating from the troposphere dissipate in the lower mesosphere to accelerate easterly winds because STPWs could not propagate in easterly wind regions. On the other hand, TRPWs develop there due to the zonal flow instability to accelerate westerly winds. The easterly wind in the mesosphere is frequently triggered by dissipation of westward TRPWs developed in the stratosphere, and would be maintained by these opposite contributions for more than 10 days. Further analyses suggest that the TRPW developing in the high-latitude lower mesosphere would be an eastward TRPW of zonal wavenumber 1 and a period of 10–40 days. This TRPW would develop and propagate downward to dismiss the baroclinic instability by eliminating warm temperature anomalies formed below the easterly wind region due to the PW dissipation in the mesosphere.
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