Daytime VLF Emissions during the Magnetic Storm Recovery Phase: the Event of January 5, 2015

This paper discusses the spectral and temporal features of the 7-h daytime VLF noise emission burst in the frequency band of 1‒10 kHz observed on the Earth’s surface during the late recovery phase of a moderate magnetic storm (Kр = 5 and Dst ~ –80 nT) under nearly quiet space weather. These VLF emissions were recorded simultaneously at two auroral stations located at a geomagnetic latitude of ~64° MLAT and at a longitude distance of ~400 km from each other: Finnish Kannuslehto Station (KAN) and Russian Lovozero Observatory (LOZ). The dynamic VLF wave spectrum is considered at different time scales. During the development of the discussed daytime VLF burst, the noise emissions at below 3.5 kHz gradually turn into periodic (QP) emissions with a quasi-repetition of ~3 s. Having compared the directions of short isolated high-frequency (above 5 kHz) VLF signals (so-called “birds”) arriving at KAN and LOZ, we draw conclusions on the possible location and spatial dynamics of the exit area of emission from the ionosphere.