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

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 cap
region and disturbances in the auroral zone. The unique analog magnetic records of the Vostok Antarctic
Observatory (corrected geomagnetic coordinates Φ' = –85.41°, Λ' = 69.01°) have been digitized with a high
frequency (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 substorms
identified by variation in AL indexes. An interruption in the mode of generation of serpentine emissions
in the region of the polar cap was found during the active phase of intense isolated substorms (with a
maximum magnitude of the AE index of ∼500–600 nT). During the expansion phase of the substorms, broadband
noise electromagnetic radiation appears with a sharp leading edge in the PC1–2 range and is also
recorded in the polar cap. Noise radiation has a sharp leading edge and occurs approximately 2 hours after
reorientation of the bz-components of the interplanetary magnetic field (IMF) from north to south. The time
of the interruption of SE coincides with the beginning this radiation and moment of achievement bz-component
of maximum negative IMF values. Interruption of the SE effect is observed against the background of
relatively stable other geoeffective parameters of the solar wind and IMF. The average duration of the interruption
of emissions is ∼3 hours. Indirect confirmation of the impact of substorm activity on the SE generation
regime is found in the coincidence of the patterns of daily and seasonal variation of SE interruption intervals
and the probability of observing substorms. Due to the fact that noise emission occurs during the active
phase of isolated substorms and ∼2 hours after reorientation of the bz-components of the IMF in the solar
wind, there is reason to believe that it is associated with plasma flows directed towards the Earth from the
magnetotail. Apparently, the energy of plasma flows during the active phase of a substorm stimulates the
appearance of noise radiation, thus interrupting SE.