Fig. 1

Panels a, d and g show the local time variation of ∆H from 1st November to 31st March for the winters of years 1980–1981, 1982–1983 and 2008–2009, respectively. The solid gray lines in the top panels represent the NAM values, while dashed gray lines correspond to the NAM value of 2 and -3 associated with the reference values for strong and weak SPV, respectively. In panels b, e and h, the amplitudes of semidiurnal solar (solid black line) tide and its climatology (dashed black line) are shown for the same years as mentioned above. In a similar way, the amplitudes of semidiurnal lunar (solid red line) tide and its climatology (dashed red line) are shown in these figures. The gray and red shadings in these panels indicate the 95% confidence intervals of semidiurnal solar and lunar tides, respectively. The error bars indicate the 95% confidence intervals of the climatological tidal amplitudes. Panels c, f and i show the averaged daily Kp values in black bars and daily F_10.7P levels in solid gray lines