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This paper presents the response of the ionosphere during the intensegeomagnetic storms of October 12-20, 2016 and May 26-31, 2017 which occurredduring the declining phase of the solar cycle 24. Total Electron Content (TEC)from GPS measured at Indore, Calcutta and Siliguri having geomagnetic dipsvarying from 32.23{\deg}N, 32{\deg}N and 39.49{\deg}N respectively and at theInternational 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 thestorms. Prominent peaks in diurnal maximum in excess of 20-45 TECU over thequiet 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 thatmeasures the thermospheric O/N2 ratio, showed high values (O/N2 ratio of about0.7) on October 16 when positive storm effects were observed compared to theother days during the storm period. The observed features have been explainedin terms of the O/N2 ratio increase in the equatorial thermosphere, CIR-inducedHigh Speed Solar Wind (HSSW) event for the October 2016 storm. The TECenhancement has also been explained in terms of the Auroral Electrojet (AE),neutral wind values obtained from the Horizontal Wind Model (HWM14) andequatorial electrojet strength from magnetometer data for both October 2016 andMay 2017 storms. These results are one of the first to be reported from theIndian longitude sector on influence of CME- and CIR-driven geomagnetic stormson TEC during the declining phase of solar cycle 24.

Effects of CME and CIR induced geomagnetic storms on low-latitude ionization over Indian longitudes in terms of neutral dynamics