Interannual variability of the spring transition date in the MLT region observed with meteor radar at Obninsk (55°N, 37°E)

► We analyse the interannual variability of the spring transition date. ► The date is estimated from winds measured at Obninsk (55°N, 37°E) with meteor radar. ► The data cover the period from 1973 to 2011. ► Correlation between the spring dates and the Northern annular mode index is −0.57. ► Correlation between the spring dates and the polar vortex breakup dates is −0.66.