Fig. 2

Two-dimensional auto-correlation functions (ACFs) as a function of lag numbers in longitude and latitude at different lag time of a − 40, b − 20, c 0, and d 20 min, obtained from the detrended TEC within the area of 133.0°–137.0° E and 33.0°–37.0° N (shown in Fig. 1) and during a period of 2 h between 14:00 and 16:00 UT on 8 June 2019. A maximum ACF for each lag time is shown by a symbol ‘ + ’ in the figure