The temperature of the polar lower stratosphere during spring is the key factor in changing the magnitude of ozone loss in the Arctic polar vortex. In this paper, we quantitatively demonstrate that the polar lower stratospheric temperature is primarily controlled by planetary-scale waves. We use National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data covering the last two decades to investigate how these planetary waves are connected to polar lower stratospheric temperatures. In particular, we show that the tropospheric eddy heat flux in middle to late winter (January--February) is highly correlated with the mean polar stratospheric temperature during March. These planetary waves are forced by both thermal and orographic processes in the troposphere and propagate into the stratosphere in the middle and high latitudes. Strong midwinter planetary wave forcing leads to a warmer spring Arctic lower stratosphere in early spring, while weak midwinter forcing leads to cooler spring Arctic temperatures. In addition, this planetary wave driving also has a strong impact on the strength of the polar vortex. ¿ 2001 American Geophysical Union