The data coverage of THU2 data in geomagnetic latitude/magnetic local time coordinates. The red circle is the data coverage (extent of pierce points) of GPS data at a cutoff elevation of 30° by assuming pierce points at 350 km altitude. The left panel shows the data coverage at 15:00 UT when THU2 is located around magnetic noon, while the right panel shows for 3:00 UT when THU2 is located around magnetic midnight. The green shaded area is the auroral oval derived from the Feldstein model for Q = 3.