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

Abstract

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.