From top to bottom: the Dst index, and the relative deviation of TEC and foF2 values with respect to monthly medians (black lines) over Cachoeira Paulista (Brazil) during the whole month of September 2015. The color lines represent the relative standard deviation (+/−) of the values taken into account for the estimation of the medians in each case. The latter is included as an indicator of the ionospheric variability in normal conditions that are used as a threshold for identifying significant ionospheric disturbances in a large scale perspective.