Geomagnetic Pulsations, Blackout and Low-Latitude Aurorae Associated with Power Magnetic Storm

The research analyzed the regularities of the dynamics of geomagnetic pulsation regimes in the frequency range 0.002–5 Hz, the generation of which reflects the interaction with the Earth's magnetosphere of the solar filament ejected by a powerful solar flare of 3B. We compared the dynamics of the change in the types and modes of geomagnetic pulsations with the dynamics of the atmosphere glow in two spectral lines and the total ionospheric absorption of radio waves. The study developed a possible model of the observed phenomenon.

Even moderate geomagnetic pulsations can cause fluctuations of <i>fo</i>F2 frequency of the auroral ionosphere

The ionosonde at the Sodankylä Geophysical Observatory (SOD; 67∘ N, 27∘ E; Finland) routinely performs vertical sounding once per minute which enables the study of fast ionospheric variations at a frequency of the long-period geomagnetic pulsations Pc5–6/Pi3 (1–5 mHz). Using the ionosonde data from April 2014–December 2015 and colocated geomagnetic measurements, we have investigated a correspondence between the magnetic field pulsations and variations of the critical frequency of radio waves reflected from the ionospheric F2 layer (foF2). For this study, we have developed a technique for automated retrieval of the critical frequency of the F2 layer from ionograms. As a rule, the Pc5–6/Pi3 frequency band fluctuations in foF2 were observed at daytime during quiet or moderately disturbed space weather conditions. In most cases (about 80 %), the coherence between the foF2 variations and geomagnetic pulsations was low. However in some cases (specified as “coherent”) the coherence was as large as γ2≥0.5. The following conditions are favorable for the occurrence of coherent cases: enhanced auroral activity (6 h maximal auroral electrojet (AE) ≥800 nT), high solar wind speed (V>600 km/s), fluctuating solar wind pressure and northward interplanetary magnetic field. In the cases when the coherence was higher at shorter periods of oscillations, the magnetic pulsations demonstrated features typical for the Alfvén field line resonance.

Registration of synchronous geomagnetic pulsations and proton aurora during the substorm on March 1, 2017

Data of synchronous geomagnetic pulsations and proton aurora registrations were analyzed during the substorm on March 1, 2017 at Zhigansk (L=4.5, induction magnetometer), Maimaga (L=4, all-sky imager and Yakutsk (L = 3.3, induction magnetometer) stations, simultaneously with satellite measurement of EMIC waves. Ground-based registration of proton aurora is very difficult due to the fact that their intensity is much lower than the aurora intensity caused by precipitations of electrons, but in the event of substorm activity at the zenith of Maimaga station, a narrow (1 degree in latitude) proton arc was observed. Irregular pulsations of the diminishing periods (IPDPs) in the range of Pc1 geomagnetic pulsations associated with the injection of energetic protons were recorded simultaneously at Zhigansk and Yakutsk stations. This is the first report when STEVE (Strong Thermal Emission Velocity Enhancement) was observed in the course of a substorm with the onset at 12:45 UT after the decay of Pc1-associated proton arc. It is shown that the proton arc and geomagnetic pulsations are a consequence of ion-cyclotron instability in the area of the outer plasmasphere overlapping by energetic protons.