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This is the first statistical ground investigation of unique low latitude Spectral Resonance Structures (SRS) that increase beyond 5Hz $5\,Hz$, crossing the fundamental Schumann resonance at few occurrences. The study is carried out using high resolution magnetic field variation data obtained from induction coil magnetometer (ICM) installed at very low latitude Indian station, Shillong (25.56°N $25.56\mathit{{}^{\circ}}\,N$ geographic latitude, 91.86°E $91.86\mathit{{}^{\circ}}\,E$ geographic longitude, dipoleL=1.08 $dipole\,L=1.08$) for the duration 2013–2018. This study focuses on the characteristics of SRS whose harmonic frequencies reach 5Hz $5\,Hz$ and above. The study reveals that the occurrence of SRS events above 5Hz $5\,Hz$ is higher in winter as compared to summer, also the occurrence is higher during low solar activity period as compared to period of solar maximum. It is seen that both the cavities, viz. Ionospheric Alfven Resonator (IAR) and Magnetospheric Alfven Resonator (MAR) support such SRS and have their respective quality factor (Q‐factor). The seasonal variability of the Q‐factor of these cavities also shows a trend similar to the occurrence, with higher values of Q‐factor during winter as compared to summer. Dependence of SRS events on parameters such as height of the IAR cavity, ion mass density, conductivities, which affects the Q‐factor reveals that IAR above 5Hz $5\,Hz$ is supported by a larger height of the cavity with very low ion densities. On the other hand, the MAR cavity efficiency is higher when the Alfven wave conductance is much larger than the Pedersen conductivity. Key Points: First statistical ground investigation of low latitude Spectral Resonance Structures with resonant harmonic frequencies above 5 HzLow latitude SRS occurrence above 5 Hz is higher during minimum solar activity, with substantially more events in winters than in summersStatistics of the quality factor of the Ionospheric Alfven Resonator and Magnetospheric Alfven Resonator, supporting the SRS is carried out [ABSTRACT FROM AUTHOR]

Substorm onset has originally been defined as a longitudinally extended sudden auroral brightening (Akasofu initial brightening: AIB) followed a few minutes later by an auroral poleward expansion in ground-based all-sky images (ASIs). In contrast, such clearly marked two-stage development has not been evident in satellite-based global images (GIs). Instead, substorm onsets have been identified as localized sudden brightenings that expand immediately poleward. To resolve these differences, optical substorm onset signatures in GIs and ASIs are compared in this study for a substorm that occurred on December 7, 1999. For this substorm, the Polar satellite ultraviolet global imager was operated with a fixed-filter (170 nm) mode, enabling a higher time resolution (37 s) than usual to resolve the possible two-stage development. These data were compared with 20-s resolution green-line (557.7 nm) ASIs at Muonio in Finland. The ASIs revealed the AIB at 2124:50 UT and the subsequent poleward expansion at 2127:50 UT, whereas the GIs revealed only an onset brightening that started at 2127:49 UT. Thus, the onset in the GIs was delayed relative to the AIB and in fact agreed with the poleward expansion in the ASIs. The fact that the AIB was not evident in the GIs may be attributed to the limited spatial resolution of GIs for thin auroral arc brightenings. The implications of these results for the definition of substorm onset are discussed herein.

We made observations of magnetic field variations in association with pulsating auroras with the magneto‐impedance sensor magnetometer (MIM) carried by the Loss through Auroral Microburst Pulsations (LAMP) sounding rocket that was launched at 11:27:30 UT on 5 March 2022 from Poker Flat Research Range, Alaska. At an altitude of 200–250 km, MIM detected clear enhancements of the magnetic field by 15–25 nT in both the northward and westward components. From simultaneous observations with the ground all‐sky camera, we found that the footprint of LAMP at the 100 km altitude was located near the center of a pulsating auroral patch. The auroral patch had a dimension of ∼90 km in latitude and ∼25 km in longitude, and its major axis was inclined toward northwest. These observations were compared with results of a simple model calculation, in which local electron precipitation into the thin‐layer ionosphere causes an elliptical auroral patch. The conductivity within the patch is enhanced in the background electric field and as a result, the magnetic field variations are induced around the auroral patch. The model calculation results can explain the MIM observations if the electric field points toward southeast and one of the model parameters is adjusted. We conclude that the pulsating auroral patch in this event was associated with a one‐pair field‐aligned current that consists of downward (upward) currents at the poleward (equatorward) edge of the patch. This current structure is maintained even if the auroral patch is latitudinally elongated. Key Points: Magneto‐impedance (MI) sensor was carried by a sounding rocket and first applied to magnetic field measurement in spaceMagnetic field variations were observed when the footprint of the payload was located near the center of an auroral patchThe magnetic field variations are thought to be caused by field‐aligned currents flowing at the edges of the pulsating auroral patch [ABSTRACT FROM AUTHOR]

The relationship between solar-wind conditions and substorm activity is modelled with an approach based on an echo state network. Substorms are a fundamental physical phenomenon in the magnetosphere–ionosphere system, but the deterministic prediction of substorm onset is very difficult because the physical processes that underlie substorm occurrences are complex. To model the relationship between substorm activity and solar-wind conditions, we treat substorm onset as a stochastic phenomenon and represent the stochastic occurrences of substorms with a non-stationary Poisson process. The occurrence rate of substorms is then described with an echo state network model. We apply this approach to two kinds of substorm onset proxies. One is a sequence of substorm onsets identified from auroral electrojet intensity, and the other is onset events identified from activity of Pi2 pulsations, which are irregular geomagnetic oscillations often associated with substorm onsets. We then analyse the response of substorm activity to solar-wind conditions by feeding synthetic solar-wind data into the echo state network. The results indicate that the effect of the solar-wind speed is important, especially for Pi2 substorms. A Pi2 pulsation can often occur even if the interplanetary magnetic field (IMF) is northward, while the activity of auroral electrojets is depressed during northward IMF conditions. We also observe spiky enhancements in the occurrence rate of substorms when the solar-wind density abruptly increases, which might suggest an external triggering due to a sudden impulse of solar-wind dynamic pressure. It seems that northward turning of the IMF also contributes to substorm occurrences, though the effect is likely to be minor. [ABSTRACT FROM AUTHOR]

The aim of this study is to provide a complete scope of a magnetic sudden impulse (SI) event along its way through interplanetary space and the magnetosphere until its arrival to the ground. In our case, we chose the event of 19th November 2007 because of the availability of enough well-located spacecraft at that moment for our purpose. We have used a 16 spacecraft data set. We calculated the mass flux variation and the change in magnetic field components across the discontinuity. Thus, we identified the solar wind discontinuity as a shock. We also calculated the orientation of the solar wind shock front. Then, we examined the effects of the shock front propagation in detail. With this large data set, we obtained a global view of the travelling wave front and identified the effects of the compressional wave front. Thus, we determined in detail the shock front passing through the different parts of the magnetosphere. We described the compressional effects in the bow shock, the magnetosheath, and the magnetopause and we depicted the propagation inside the inner magnetosphere. Moreover, we used an extensive data set from magnetic observatories on the ground and so we studied the global distribution of the SI waveform. Finally, the comparison of the observational facts with those derived from the theoretical model showed a good consistency. On the basis of the waveforms and polarizations of this SI, we determined the location in latitude where ionospheric currents (ICs) changed their sense. And also, we related polarization at ground to polarization measured by GOES spacecraft.