Figure 3

Magnitudes of wave driving in (a) tropical and (b) polar stratopause regions, (c) latitude of the subtropical zero wind line and (d) the amplitudes of wave number 1 and 2 planetary waves at 60° N, 1 hPa level during the SSW event of 2000–2001. The thin lines and the shadings in (a,b) represent the long term (1979–2021) mean wave driving and its standard deviation, respectively. Vertical blue dashed line represents the day on which winds in the polar cap at 10 hPa level reverses to westward. Red dashed line represents the day of wind reversal at 60° N, 10 hPa level. Wave driving at the stratopause is averaged for the reanalysis pressure levels 2 hPa to 0.7 hPa for tropics from 7.5 to 12.5° N (averaging to 10° N) and for polar regions from 57.5 to 62.5° N (averaging to 60° N). This averaging is done to minimize errors due to considering single latitude and pressure levels.