Correlation between IGS TEC and E _m at each grid point of the IGS TEC maps in the time period of 01.01.2013 ±45 days, computed for a shifted solar wind by lag hours ranging from 0 to 48 h. The results are converted into geomagnetic coordinates (quasi dipole latitude in circles and magnetic local time in radial lines) and averaged over all UTs. Left: maximum correlation coefficient from the different lag hours. Right: lag hours at which the maximum correlation occurs (contour lines present the maximum correlation shown in the left panel).