  We developed a new technology for global detection of atmospheric
disturbances, on the basis of phase measurements of the total electron content
(TEC) using an international GPS networks. Temporal dependencies of TEC are
obtained for a set of spaced receivers of the GPS network simultaneously for
the entire set of visible satellites. These series are subjected to filtering
in the selected range of oscillation periods using known algorithms for
spatio-temporal analysis of signals. An "instantaneous" ionospheric response to
the sudden commencement of a strong magnetic storm of April 6, 2000 was
detected. On the dayside of the Earth the largest value of the net response
amplitude was found to be of order 0.8*10^16 m^-2 (1--2 % of the background TEC
value), and the delay with respect to the SC in mid-latitudes was about 200 s.
In higher latitudes the delay goes as long as 15 min. On the nightside these
values are 0.2*10^16 m^-2 and 30 min, respectively. The velocity of the
traveling disturbance from the middle to high latitudes on the dayside as well
as from the dayside to the nightside was about 10-20 km/s.
