Characterization of Positive and Negative Ionospheric Storm Phases Using TNPGN-Active TEC Estimates Spanning Solar Cycles 24 and 25 (2019-2023)
DOI:
https://doi.org/10.61326/jaasci.v5i1.481Keywords:
Geomagnetic storm, GNSS-TEC, Ionospheric storm, Mid-latitude ionosphere, Solar Cycle 24-25, TNPGN-ActiveAbstract
Geomagnetic storms induce significant perturbations in the ionosphere, profoundly affecting Total Electron Content (TEC) and consequently the performance of Global Navigation Satellite Systems (GNSS). This study characterizes the positive and negative phases of ionospheric storms over Türkiye during 14 geomagnetically disturbed days (maximum 3-hourly Kp > 6, corresponding to G2–G4 storms on the NOAA scale) spanning January 2019 to June 2023. The period covers the deep minimum of Solar Cycle 24 (SC24) and the ascending phase of Solar Cycle 25 (SC25). High-resolution IONOLAB-TEC estimates at 2.5-minute intervals are derived from nine continuously operating stations of the Turkish National Permanent GNSS Network-Active (TNPGN-Active). These stations, distributed across geodetic latitudes 36.59°N-42.01°N and longitudes 26.33°E-44.34°E, provide comprehensive spatial coverage of the mid-latitude ionosphere over the Eastern Mediterranean and Anatolian region. A single geomagnetically quiet reference day (07 May 2022) is selected and an observation-driven pre-storm scaling procedure is applied to normalize the TEC time series. This approach effectively accounts for seasonal and solar-cycle differences in background ionization levels without dependence on empirical models. Analysis of network-averaged normalized TEC deviations ( ) reveals that storm responses are governed by a complex interplay of factors. Storm intensity provides a first-order control on perturbation magnitude, with G4 events generally producing larger peak positive deviations. However, the local time of storm onset strongly modulates phase dominance: near-noon onsets favor prolonged negative phases associated with thermospheric composition changes, while midnight-to-morning onsets promote extended positive phases driven by prompt penetration and disturbance dynamo electric fields. Seasonal dependence is pronounced, with spring events displaying the most consistent positive responses, winter conditions amplifying relative enhancements due to lower baseline TEC and summer suppressing both phases. Pre-storm scaling factors clearly reflect the solar-cycle transition, showing a roughly twofold increase in background TEC from the SC24 minimum to early SC25. These results establish a regional observational baseline for mid-latitude ionospheric storm morphology in an underrepresented longitude sector. They highlight the value of dense GNSS networks and observation-based normalization techniques for advancing space weather understanding and improving GNSS reliability as Solar Cycle 25 approaches its maximum.
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