Under normal wintertime conditions, when the wind blows from west-to-east, the largest atmospheric waves can travel through the stratosphere. However, if a major disruption of the stratospheric polar vortex occurs, the winds in the middle stratosphere reverse direction and blow from east-to-west, and the temperature warms. Large atmospheric waves cannot travel through winds blowing in this direction, so the next wave to travel into the stratosphere breaks just below where the reversal occurred. This “wave breaking” can reverse the winds in this lower layer, so that again, the next wave to travel into the stratosphere breaks even lower. In this way, the changes in the winds and temperatures in the middle stratosphere can descend to the tropopause, which represents the transition between the stratosphere and the troposphere. NOAA Climate.gov image.