  We present the results from nearly three years of monitoring of the
variations in dispersion measure (DM) along the line-of-sight to 11 millisecond
pulsars using the Giant Metrewave Radio Telescope (GMRT). These results
demonstrate accuracies of single epoch DM estimates of the order of 5x10^(-4)
cm^(-3) pc. A preliminary comparison with the Parkes Pulsar Timing Array (PPTA)
data shows that the measured DM fluctuations are comparable. We show effects of
DM variations due to the solar wind and solar corona and compare with the
existing models.

High Energy Astrophysical Phenomena;Instrumentation and Methods for Astrophysics