Lagged Pearson correlation values of 1-hour resampled EISCAT TEC and OMNI merging electric field E_m between the time range of 18 and 6 UT on 9–12 January 2013 (left top), 2–6 February 2019 (right top), 19–29 January 2010 (left bottom), and 6–9 February 2007 (right bottom). Pink represents the E-region of the ionosphere (90–150 km), green the F-region (150–500 km), and lilac the combined region (90–500 km). The shaded area corresponds to the 0.95 confidence level of the correlation coefficient.