The Effect of Interruption of "Serpentine Emission" (SE) in the Polar Cap during Geomagnetic Storm Sudden Commencements (SSC)

The behavior of the carrier frequency of electromagnetic emission in a range of 0.1-5 Hz of the "serpentine emission" (SE) type, which is observed in the polar cap region during geomagnetic storm sudden commencements (SSC), is studied. The unique analog magnetic records of the Vostok Antarctic observatory (corrected geomagnetic coordinates phi' = -85.41 degrees, ?' = 69.01 degrees), which have been digitized at high resolution (20 Hz) and are freely available on the website of the World Data Center for the Solar-Terrestrial Physics, Moscow, are used for the analysis. It is found that at the time of SSC at the Vostok observatory, a noise broadband electromagnetic emission was observed in the Pc1-2 range with a sharp edge, which led to a violation of the SE generation mode. The disruption of the SE excitation manifested itself in the interruption of the carrier frequency of emission with the subsequent renewal. In this paper, 92 cases of SSC observations were studied, for which the SE recording data were available. The effect of SE interruption during SSC was noted in more than 80% of cases, regardless of the fact whether or not a geomagnetic storm subsequently developed and of the storm intensity. The "serpentine emission" that lasted continuously for hours and even days was interrupted at the SSC moment in the dominant number of cases for approximately 2-3 h, which is significantly less than the average duration of the main phase and the duration of the storm itself. It is shown that the SE carrier frequency gradually decreased approximately 2 h before the SSC moment. It is assumed that an interplanetary disturbance, following the shock wave front, excites a broadband noise emission in the polar cap, which violates the SE generation mode.