Quiet Time Enhancements and Decrements in the Day-to-Day TEC Variations Over the Indian Equatorial and Low Latitudes

The low latitude ionosphere exhibits complex day-to-day variability, even during geomagnetically quiet conditions, posing significant challenges in satellite-based applications. These variations arise from a complex interplay between electrodynamic and neutral dynamic processes, including the wave forcing from below, such as planetary waves and tides. Understanding the mechanisms governing day-to-day ionospheric variations is essential for improved characterization of the low latitude ionosphere. This study investigates quiet time day-to-day ionospheric Total Electron Content (TEC) variations using GPS observations at four identified locations from the equator to the EIA crest and beyond in the Indian sector. Strong enhancements and decrements are observed in day time TEC variations under quiet geomagnetic conditions (Kp < 3). A total of 25 deviation events in TEC spanning over 200 days are observed at different latitudes during a 3-year period covering different solar activity conditions. These deviations occur more during summer months of high solar activity with distinct latitudinal dependence. Detailed analysis using equatorial electrojet observations revealed that the electric field variations could not always explain the observed TEC deviations. Wavelet analysis revealed the presence of the periods of 2–6 days in TEC during the events of TEC deviations. Possible drivers of the quiet time day-to-day TEC deviations are explained in terms of the planetary wave forcing through distinct latitude dependent processes. This study provides new insights into the relative contributions of wave forcing from below through coupled ionosphere-thermosphere dynamics and offers a greater understanding of the physical mechanisms governing the quiet time TEC variabilities over the equatorial and low-latitude regions.