Investigation of ionosphere response to geomagnetic storms over the propagation paths of very low frequency radio waves

Diagnostic study of geomagnetic storm-induced ionospheric changes over VLF signal propagation paths in mid-latitude D-region

“…f oF2, f oF1, f oE, f oEs, h F2, h E, h Es) exhibit 11-year solar cycle evolution (Ouattara et al, 2009). This characteristic demonstrates their sensitivity to solar activity (Nwankwo et al, 2020d), and therefore, a strong indication that space weather effects on the ionosphere can be monitored using these parameters. In this work, we combine the observed diurnal VLF amplitude variation in the D-region with HF radio pulses in the E and F regions (ionosonde) to perform a diagnostic investigation of coupled geomagnetic storm effects, in order to understand the observed storm-induced variations in VLF narrowband based on the state and responses of ionosphere.…”

“…Substantial progress has been made in understanding global dynamics and large-scale coupling of the upper ionosphere using both ground-based observational capabilities (e.g., Global Navigation Satellite System (GNSS) receivers, vertical and oblique high frequency (HF) sounding, atmospheric radar (coherent and incoherent scatter radars)) and space-based satellite systems (e.g., Advance Composition Explorer (ACE), Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), Defense Meteorological Satellite Program (DMSP), Geostationary Operational Environmental Satellite (GOES) etc.) (Nwankwo et al, 2020d). However, the physics of lower ionospheric coupling in terms of solar wind driving remains a major scientific gap because of the limited observational capabilities in the lower 2 https://doi.org/10.5194/angeo-2021-42 Preprint.…”

“…They also observed some incidences of MDP signal rise (or, increase) during some storms despite significant dipping in majority of the signal. Nwankwo et al (2020d) noted that some signal propagation paths may not exhibit the storm-induced dipping and/or may do so for some storms due to factors such as mode interference, propagation path and anti-correlated responses of VLF signal to a combination of storm induced and/or enhanced ionospheric phenomena (e.g., prompt penetration electric fields (PPEFs) and disturbance dynamo electric field (DDEF)), and strong solar flares occuring simultaneously. However, to understand their propagation characteristics it is important to monitor the state of the ionosphere over the propagation paths of VLF radio waves when probing ionospheric irregularities using the signal (Nwankwo et al, 2020d).…”

“…Nwankwo et al (2020d) noted that some signal propagation paths may not exhibit the storm-induced dipping and/or may do so for some storms due to factors such as mode interference, propagation path and anti-correlated responses of VLF signal to a combination of storm induced and/or enhanced ionospheric phenomena (e.g., prompt penetration electric fields (PPEFs) and disturbance dynamo electric field (DDEF)), and strong solar flares occuring simultaneously. However, to understand their propagation characteristics it is important to monitor the state of the ionosphere over the propagation paths of VLF radio waves when probing ionospheric irregularities using the signal (Nwankwo et al, 2020d). This will require simultaneous combination of observed VLF amplitude/phase variations in the lower ionosphere with parameter that defines the state of the ionospheric (e.g., total electron content (TEC), ionosode etc.)…”

“…In this work, we combine the observed diurnal VLF amplitude variation in the D-region with HF radio pulses in the E and F regions (ionosonde) to perform a diagnostic investigation of coupled geomagnetic storm effects, in order to understand the observed storm-induced variations in VLF narrowband based on the state and responses of ionosphere. Similar analysis (or study) has also been done using TEC/VTEC indices (Nwankwo et al, 2020d).…”