17:15 〜 19:15
[PEM12-P33] Ionospheric response to solar flares – how fast does the disturbance propagate?
キーワード：Ionosphere, Solar Flares, Sudden Ionospheric Disturbance, GNSS, TEC
A Solar Flare (SF) is a tremendous explosion on the Sun that is characterised by the increased radiation in the X-ray and in the ultraviolet (UV), a stream of a wide range of energy particles. Several effects are caused when they come into contact with the atmosphere of the Earth, including Sudden Ionospheric Disturbances (SID), which are a collective term for the quick rise in ionospheric ionization resulting from increased X and UV radiation.
It is generally assumed that the SID occurs instantly and simultaneously on the entire dayside. In this work, we use high-rate 1 sec data of ionospheric total electron content (TEC) from world-wide distributed receivers of the Global Navigation Satellite Systems (GNSS), and we analyze the global dayside TEC response to thirteen solar flares that occurred between 2003 and 2023. The high temporal resolution allowed us, for the first time, to observe the propagation of SID from the subsolar point to the dusk regions. We find that the apparent velocity of SID propagation varies between ~250 and ~500 km/s, and might depend on the position of the flare on the solar disk (on disk and limb, respectively).
In addition, we noted that the apparent SID propagation is anisotropic, i.e., depending on the observation’s location relatively to a sub-solar point. The velocity of the enhancement varies in a different part of dayside of the ionosphere. We performed modelling of SID effects and investigated the possible reasons which can be responsible for this effect, including background level of ionization, solar-zenith angle dependency and thermospheric composition changes.
Figure. The development of SID as seen in TTD of dTEC/dt parameter (left panel) and Global dTEC/dt Maps (right panels) for the 20 September 2023 M8.2 flare.
It is generally assumed that the SID occurs instantly and simultaneously on the entire dayside. In this work, we use high-rate 1 sec data of ionospheric total electron content (TEC) from world-wide distributed receivers of the Global Navigation Satellite Systems (GNSS), and we analyze the global dayside TEC response to thirteen solar flares that occurred between 2003 and 2023. The high temporal resolution allowed us, for the first time, to observe the propagation of SID from the subsolar point to the dusk regions. We find that the apparent velocity of SID propagation varies between ~250 and ~500 km/s, and might depend on the position of the flare on the solar disk (on disk and limb, respectively).
In addition, we noted that the apparent SID propagation is anisotropic, i.e., depending on the observation’s location relatively to a sub-solar point. The velocity of the enhancement varies in a different part of dayside of the ionosphere. We performed modelling of SID effects and investigated the possible reasons which can be responsible for this effect, including background level of ionization, solar-zenith angle dependency and thermospheric composition changes.
Figure. The development of SID as seen in TTD of dTEC/dt parameter (left panel) and Global dTEC/dt Maps (right panels) for the 20 September 2023 M8.2 flare.