Histograms of the time between observations of ion-acoustic waves Δt from LFR and TDS and the nearest strong current structure identified by PVI values greater than 5 for τ = 1 s (blue), 10 s (red), and 60 s (gold). (a) Histograms of Δt for ion-acoustic waves observed by LFR. (b) Histograms of Δt for LFR snapshots where we do not identify ion-acoustic waves. (c) Histograms of Δt for ion-acoustic waves observed by TDS. (d) Histograms of Δt for TDS snapshots where we do not identify ion-acoustic waves. The points at Δt = 10⁻¹ s are snapshots at or within current structures.