Fig. 1

ISR-Swarm conjunctions for Swarm A (top), Swarm B (middle) and Swarm C (bottom) panels. SLIDEM is on the left; L1b is on the right. The dashed black lines denote orthogonal-least-squares regression fits to the data, while the solid cyan line denotes a theoretical ‘ideal’ one-to-one correspondence. Both x- and y-axes are in units of MHz (plasma frequency) rather than density, following Lomidze et al. (2018) and references therein. The errors are given as standard errors at 95% confidence