Authors: Lekshmi O Nair
Abstract: The equatorial and low-latitude ionosphere over the Indian region has undergone significant changes during the past 25 years (2000-2025), spanning three complete solar cycles. This comprehensive review synthesizes observational evidence from ground-based ionosondes, GPS Total Electron Content (TEC) measurements, satellite missions, and space weather monitoring networks across the Indian longitude sector (60°E-100°E). Key findings reveal systematic variations in the Equatorial Ionization Anomaly (EIA) morphology, with the northern crest showing enhanced TEC values during solar maximum periods and distinctive seasonal asymmetries. Equatorial Spread F (ESF) and plasma bubble occurrence demonstrate strong correlations with solar flux variations, geomagnetic activity, and atmospheric tidal forcing. The review highlights technological advances including the Indian Network for Space Weather Impact Monitoring (InSWIM), improved ionospheric models, and enhanced prediction capabilities. Significant space weather events, including the 2003 Halloween storms, 2015 St. Patrick's Day event, and recent solar cycle 25 disturbances, have provided insights into ionosphere-magnetosphere coupling processes. Climate change effects on the upper atmosphere are emerging as new research frontiers, with evidence for long-term trends in ionospheric parameters. Future challenges include understanding mesosphere-lower thermosphere-ionosphere coupling, developing regional ionospheric models for navigation applications, and preparing for increasing space weather threats to technological infrastructure.
DOI: http://doi.org/10.5281/zenodo.18242035
