Figure 2. Two typical strong SIDs observed at 13.6 kHz. (top) Event that took place on Omega (Haiku)-Sao Paulo path (d = 12.9 Mm) when the Sun was active, and nearly no effect was found in amplitude. (bottom) Event on Omega (NDAK)-Sao Paulo path (d = 9.35 Mm), showing important amplitude fading under the quiet Sun conditions [Rizzo Piazza and Kauffman, 1975].