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Fig. 6 | Progress in Earth and Planetary Science

Fig. 6

From: Day-to-day and short-term variabilities in the equatorial plasma bubble/spread F irregularity seeding and development

Fig. 6

a Top panel: F layer height oscillations at 8-MHz plasma frequency obtained by band-pass filtering (0.5–1.5 h period) of the true height measured at 5 and 7.5-min cadence by a Digisonde at Cachimbo, Brazil. The superposed oscillations for a selected set of days (from a 66-day period) are nearly in-phase (coherent) on all days. Middle panel: Similar plots for the group of remaining days of the 66-day period that show the oscillations mostly in random phase. The gray segment of each curve in both panels shows transition to spread F activity after sunset, with non-spread F hours continuing colored. Bottom panel: The mean of vertical drifts calculated as Vz = dhF/dt separately for the above two groups of days. (These data are from the COPEX Campaign, Abdu et al. 2009c at Cachimbo, LT = UT–3 h 40 min.) b Similar results as in Fig. 6a, but for the period of 1–31 October 2008 over Fortaleza, where LT = UT–2 h 32 min

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