Alfven echo of giant ground loop current

Here are presented experimental results concerning the registration by ground magnetometers of artificial MHD echo generated by powerful pulse current in ground loop contour. Data analysis was made of several magnetic stations for 16 experiments with giant loop-current contour giving magnetic flux 10⁶nT/km² (the current attained 20 kA). Only several rather weak bursts were registered which appeared 78±2s after main switch impulse. Echo signal was a few nanotesla. Taking into account real magnetosphere tube configuration for L ≈ 5,5 and Kp≤2 it was shown that the signal with such a delay corresponds to propagation of artificial excited Alfven echo, returning back from a magnetoconjugate ionospheric region. Meanwhile, the amplitude exceed by one order the theoretically calculated one.