  This paper presents the response of the ionosphere during the intense
geomagnetic storms of October 12-20, 2016 and May 26-31, 2017 which occurred
during the declining phase of the solar cycle 24. Total Electron Content (TEC)
from GPS measured at Indore, Calcutta and Siliguri having geomagnetic dips
varying from 32.23{\deg}N, 32{\deg}N and 39.49{\deg}N respectively and at the
International GNSS Service (IGS) stations at Lucknow (beyond anomaly crest),
Hyderabad (between geomagnetic equator and northern crest of EIA) and Bangalore
(near magnetic equator) in the Indian longitude zone have been used for the
storms. Prominent peaks in diurnal maximum in excess of 20-45 TECU over the
quiet time values were observed during the October 2016 storm at Lucknow,
Indore, Hyderabad, Bangalore and 10-20 TECU for the May 2017 storm at Siliguri,
Indore, Calcutta and Hyderabad. The GUVI images onboard TIMED spacecraft that
measures the thermospheric O/N2 ratio, showed high values (O/N2 ratio of about
0.7) on October 16 when positive storm effects were observed compared to the
other days during the storm period. The observed features have been explained
in terms of the O/N2 ratio increase in the equatorial thermosphere, CIR-induced
High Speed Solar Wind (HSSW) event for the October 2016 storm. The TEC
enhancement has also been explained in terms of the Auroral Electrojet (AE),
neutral wind values obtained from the Horizontal Wind Model (HWM14) and
equatorial electrojet strength from magnetometer data for both October 2016 and
May 2017 storms. These results are one of the first to be reported from the
Indian longitude sector on influence of CME- and CIR-driven geomagnetic storms
on TEC during the declining phase of solar cycle 24.
