(a)

The solar cycle phases dependence of the storm strength

Minimum

Increasing

Maximum

Decreasing

max ${\text{ΔfoF2}}_{\text{Hourly}}$ in MHz

2.607

4.670

2.270

2.300

(b)

The seasonal dependence of the storm strength

Winter

Summer

Spring

Autumn

max ${\text{ΔfoF2}}_{\text{Hourly}}$ in MHz

1.443

6.227

1.774

2.203