In this study,fields of wind and temperature from the ERA-Interim reanalysis for the period of 1980-2000 are used to calculate the Eliassen-Palm flux and its divergence of planetary waves in the Northern Hemisphere winter.Next,the characteristics of decadal-scale variability throughout the layer of stratospheric temperature and wind and the relationships to changes in planetary wave activity during December and January-February are analyzed.While the high-latitude middle and lower stratosphere show a warming tendency in December,the same region cools during January-February.The zonal-mean zonal winds in the mid-to-high latitude middle and upper stratosphere decelerate evidently in December,but show a significant accelerated tendency during January-February with increasing latitude and altitude in the high-latitude middle and upper stratosphere.The planetary waves mainly propagate upward along the low-latitude and polar wave guides in the Northern Hemisphere winter.However,in December the propagation along the low-latitude wave guide decreases,whereas that along the polar wave guide and throughout the entire layer stratosphere increases evidently.On the contrary,during January-February the propagation along the low-latitude wave guide strengthens significantly,whereas that along the polar wave guide and throughout the stratosphere weakens.Therefore,during December and January-February for the period of 1980-2000,the respective situations of the decadal-scale changes of wave-mean flow interactions in the Arctic stratosphere tend to be opposite,and it is necessary to discuss the decadal variability during different winter months on a case-by-case basis.