Spectrum of frequency modulation of serpentine emission as a reflection of the solar fluctuation spectrum

We examine the characteristics of oscillations of two types in the high-frequency edge of the ULF range (0.1–3 Hz), serpentine emission (SE), and discrete frequency dispersed signals (DS). Oscillations of both the types are observed in the polar caps exclusively with induction magnetometers. Since these instruments are currently practically absent at high latitudes, the analysis has been carried out from records obtained at the stations Vostok and Thule close to the geomagnetic poles in 1968–1971. The DS occurrence rate is shown to have a sharp peak at local magnetic noon. This fact indicates that DS emergence is rigidly tied to the geomagnetic field line passing through the observation station. At the same time, the seasonal variation in the frequency of DS occurrence has a main peak in local summer and an additional peak in local winter. We have revealed before that at least a part of DS is excited in the foreshock region. Taking this into account, we can assume that the wave packets incident to the magnetopause fall on the external field lines mainly in the noon region and propagate along these lines in both directions, eventually reaching Earth’s surface in the polar regions. Unlike DS, the SE occurrence rate has neither a daily nor a seasonal variation. We have tested and confirmed indirectly the hypothesis put forward earlier about the excitation of SE by cyclotron instability of protons in the solar wind, simulating frequency variations in ion-cyclotron waves at different levels of interplanetary plasma perturbation and comparing the results with the SE frequency variations observed under similar conditions. We conclude that it is necessary to resume continuous observations of ULF emissions, using induction magnetometers installed in polar caps near the projections of cusps and near geomagnetic poles.

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Features of the Behavior of SE-Type Radiation during a Substorm

Kurazhkovskaya,

Kline

2023

Geomagnetizm i aèronomiâ

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A study was made of simultaneous observations of ultra-low-frequency oscillations in the 0.1–5.0 Hz frequency range of the serpentine emissions type (Serpentine Emissions, SE) observed at the polar capregion and disturbances in the auroral zone. The unique analog magnetic records of the Vostok AntarcticObservatory (corrected geomagnetic coordinates Φ' = –85.41°, Λ' = 69.01°) have been digitized with a highfrequency (20 Hz) and are freely available on the website of the World Data Center for Solar-Terrestrial Physics,Moscow. For 1966 (November and December), 1968 (March–July), and 1970–1972, 1973 (January–March) the behavior of “serpentine emissions” was analyzed during the development of 180 isolated substormsidentified by variation in AL indexes. An interruption in the mode of generation of serpentine emissionsin the region of the polar cap was found during the active phase of intense isolated substorms (with amaximum magnitude of the AE index of ∼500–600 nT). During the expansion phase of the substorms, broadbandnoise electromagnetic radiation appears with a sharp leading edge in the PC1–2 range and is alsorecorded in the polar cap. Noise radiation has a sharp leading edge and occurs approximately 2 hours afterreorientation of the bz-components of the interplanetary magnetic field (IMF) from north to south. The timeof the interruption of SE coincides with the beginning this radiation and moment of achievement bz-componentof maximum negative IMF values. Interruption of the SE effect is observed against the background ofrelatively stable other geoeffective parameters of the solar wind and IMF. The average duration of the interruptionof emissions is ∼3 hours. Indirect confirmation of the impact of substorm activity on the SE generationregime is found in the coincidence of the patterns of daily and seasonal variation of SE interruption intervalsand the probability of observing substorms. Due to the fact that noise emission occurs during the activephase of isolated substorms and ∼2 hours after reorientation of the bz-components of the IMF in the solarwind, there is reason to believe that it is associated with plasma flows directed towards the Earth from themagnetotail. Apparently, the energy of plasma flows during the active phase of a substorm stimulates theappearance of noise radiation, thus interrupting SE.

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Spectrum of frequency modulation of serpentine emission as a reflection of the solar fluctuation spectrum

Cited by 4 publications

References 6 publications

On Geoseismic Noise and Helioseismic Oscillations

On Geoseismic Noise and Helioseismic Oscillations

Ultra low frequency emissions ranging from 0.1 to 3 Hz in circumpolar areas

Features of the Behavior of SE-Type Radiation during a Substorm

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