Evolution and drift of Plasma depletions from GPS Data 
 
S. Gopi Krishna, P. Doherty and C.E. Valladares 
 
Abstract: 
The ionospheric TEC and L-band scintillations are the most affecting factors in 
degrading the accuracy in the implementation of navigation systems such as SBAS, 
particularly in the low latitude and equatorial regions. It is well established 
that plasma depletions/bubbles are often associated with scintillations, at the 
edge of these depletions strong electron density gradients are present resulting 
in intense scintillations at the GPS L-band frequencies owing to the presence of 
the small scale irregularities. Thus a prior knowledge on the extent and 
movement of the bubbles will be of immense use in mitigation of range errors the 
GPS based navigation systems. 
 
In this paper, we present the evolution and extent of the total electron content 
(TEC) depletions/bubbles derived from the simultaneous observations of TEC and 
scintillation data from available GPS TEC stations of Low-latitude Ionospheric 
Sensor Network (LISN) and South American region. The threshold values of dTEC 
for the detection of the bubbles are computed and defined after removal of the 
diurnal variability in TEC, and simultaneously verified with the presence of 
scintillations. The evolution and propagation of the TEC depletions are detected 
from the simultaneous TEC data from different satellites as well from different 
GPS stations. The attempts to compute the east-west drifts and size of the 
depletions are from the simultaneous detection of bubbles and prediction of 
northward/east-west extent of scintillation patches and their movement into the 
neighboring ionospheric grid point (IGP) are also presented.