  We have investigated a dependence of the relative density of phase slips in
the GPS navigation system on the disturbance level of the Earth's
magnetosphere. The study is based on using Internet-available selected data
from the global GPS network, with the simultaneously handled number of
receiving stations ranging from 160 to 323. The analysis used four days from
the period 1999-2000, with the values of the geomagnetic field disturbance
index Dst from 0 to -300 nT. During strong magnetic storms, the relative
density of phase slips on mid latitudes exceeds the one for magnetically quiet
days by one-two orders of magnitude as a minimum, and reaches a few and (for
some of the GPS satellites) even ten percent of the total density of
observations. Furthermore, the level of phase slips for the GPS satellites
located on the sunward side of the Earth was by a factor of 5-10 larger
compared with the opposite side of the Earth. The high positive correlation of
an increase in the density of phase slips and the intensity of ionospheric
irregularities during geomagnetic disturbances as detected in this study points
to the fact that the increase is slips is caused by the scattering of the GPS
signal from ionospheric irregularities.
