Fig. 3From: Morphology of sporadic E layers derived from Fengyun-3C GPS radio occultation measurementsMonthly variations of the number of all FY-3C RO measurements (in blue), the number of RO measurements valid for Es-layer detection (in red), the number of RO observations detected with Es layers (in yellow), and the Es occurrence rates (in black, right y-axis), during 2015 to 2019Back to article page