  The Earth's ionosphere introduces systematic effects that limit the
performance of a radio interferometer at low frequencies ($\lesssim 1$\,GHz).
These effects become more pronounced for severe geomagnetic activities or
observations involving longer baselines of the interferometer. The uGMRT, a
pathfinder for the Square Kilometre Array (SKA), is located in between the
northern crest of the Equatorial Ionisation Anomaly (EIA) and the magnetic
equator. Hence, this telescope is more prone to severe ionospheric conditions
and is a unique radio interferometer for studying the ionosphere. Here, we
present 235\,MHz observations with the GMRT, showing significant ionospheric
activities over a solar minimum. In this work, we have characterised the
ionospheric disturbances observed with the GMRT and compared them with
ionospheric studies and observations with other telescopes like the VLA, MWA
and LOFAR situated at different magnetic latitudes. We have estimated the
ionospheric total electron content (TEC) gradient over the full GMRT array
which shows an order of magnitude higher sensitivity compared to the Global
Navigation Satellite System (GNSS). Furthermore, this article uses the
ionospheric characteristics estimated from the observations with uGMRT, VLA,
LOFAR and MWA to forecast the effects on the low-frequency observations with
the SKA1-MID and SKA1-LOW in future.
