Variations of the gridded mean Δf_oF₂ with increasing <ap>_24 h at the northern hemisphere stations (from top to bottom: Dikson, Norilsk, Yakutsk, Petropavlovsk, Irkutsk, Wakkanai, Kokubunji, Yamagawa, and Okinawa); the error bars indicate the lower and upper quartiles of the gridded Δf_oF₂. (a–d) present the variations under the seasonal conditions of March equinox, June Solstice, September equinox, and December solstice, respectively.