Figure 1
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Long-term variation of the SF occurrence at EB040. Panel (a) shows the FSF occurrence rate derived from the 1-h scaled foF2 from 1955 to 2019. Panel (b) shows the occurrence rate of SF, considering both FSF and RSF, from the 5-min ionogram measurements from 2012 to 2022. The dotted red rectangle in Panel (a) represents the same interval (2012–2019) as shown in Panel (b).
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