Physics of auroral phenomena : proceedings of the 40th annual seminar, Apatity, 13-17 March, 2017 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2017. - 143 с. : ил., табл.

“Physics o f Auroral Phenomena”, Proc. XL Annual Seminar, Apatity, pp. 50-53, 2017 © Polar Geophysical Institute, 2017 Polar Geophysical Institute CHANGE IN THE SPECTRAL FEATURES OF QP EMISSIONS DUE TO POLEWARD MAGNETIC BAY J. Manninen1, N.G. Kleimenova2, L.I. Gromova3, E.L. Macotela1, T. Turunen1, A.E. Kozlovsky1 1Sodankyla Geophysical Obsei'vatory, Sodankyla, Finland 2Schmidt Institute o f Physics o f the Earth (IFZ RAN), Moscow, Russia 3Pushkov Institute o f Terrestrial Magnetism, Ionosphere, and Radiowave Propagation, (IZMIRAN), Troitsk, Moscow, Russia Abstract. Here we discuss a short-time significant change in the spectral features of quasi-periodic VLF emissions observed by ground-based receiver at Kannuslehto (KAN, northern Finland, L = ~ 5.5) in the local evening under quiet geomagnetic conditions (Kp~0-1) on 24 December 2011. This event was previously discussed by [Manninen et al., 2012, 2014]. It was shown_the peculiar dynamic spectral structure of repeated long-lasting (up to two minutes) noise bursts with quickly rising frequency up to ~ 5.5 kHz. The relatively stable wave structure suddenly changed at the time, when a small isolated substorm was recorded at the polar geomagnetic latitudes higher than 70° by the IMAGE magnetometers. The AMPERE data showed the magnetic bay-like disturbances and the enhanced field aligned currents at polar latitudes aligned from Svalbard to the East (up to Dixon station). There was no significant geomagnetic and ionospheric activity at Sodankyla (i.e. in the vicinity of VLF receiver). The low frequency VLF (f< 1.7 kHz) waves suddenly occurred and the wave arriving direction changed as well. The dynamic spectra were also modified. KAN monitored also the amplitude of the navigation (f~20-25 kHz) transmitter signals, which involved the polar-latitude propagation paths, showed some variations during this time. We conclude that VLF emission behaviour observed on the ground could be a very sensitive proxy for influence of even short small poleward geomagnetic disturbances to the VLF wave generation and wave propagation properties. Introduction We continue the comprehensive analysis of the quasi-periodic (QP) VLF emissions event [Manninen et a l, 2012, 2014] recorded at Kannuslehto (KAN, northern Finland, at L = ~ 5.5, Fig. 1) on 24 December 2011 under quiet geomagnetic conditions (Kp ~ 0-1). The studied QP emissions were right-hand polarized (indicating that KAN was located in the vicinity of the ionospheric exit point o f the waves) and their frequency rapidly rose up to ~ 5.5 kHz. Very stable spectral shape of QP emissions was suddenly changed at time o f occurrence of a small poleward magnetic substorm. The aim o f this paper is to study this change in detail. Observation Geomagnetic conditions. The relatively stable OP wave structure suddenly changed, when the IMAGE magnetometers recorded a small isolated substorm at the polar geomagnetic latitudes higher than 70° (Fig. 2). There was no significant geomagnetic nor ionospheric activity at Sodankyla station (i.e. in the vicinity of the VLF receiver). Figure 1 . The map o f IMAGE stations. Figure 2. IMAGE magnetograms. Figure 3. The AMPERE data. 34 D ec 2011 a*a* act*: tsaooo- twooour 50