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Correlation of Very Low and Low Frequency Signal Variations at Mid-Latitudes with Magnetic Activity and Outer-Zone Particles

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Correlation of Very Low and Low Frequency Signal Variations at Mid-Latitudes with Magnetic Activity and Outer-Zone Particles Ann. Geophys., 32, 1455–1462, 2014 www.ann-geophys.net/32/1455/2014/ doi:10.5194/angeo-32-1455-2014 © Author(s) 2014. CC Attribution 3.0 License. Correlation of very low and low frequency signal variations at mid-latitudes with magnetic activity and outer-zone particles A. Rozhnoi1, M. Solovieva1, V. Fedun2, M. Hayakawa3, K. Schwingenschuh4, and B. Levin5 1Institute of Physics of the Earth, Russian Academy of Sciences, 10 B. Gruzinskaya, Moscow, 123995, Russia 2Space Systems Laboratory, Department of Automatic Control and Systems Engineering, University of Sheffield, Sheffield, S1 3JD, UK 3University of Electro-Communications, Advanced Wireless Communications Research Center, 1-5-1 Chofugaoka, Chofu Tokyo, 182-8585, Japan 4Space Research Institute, Austrian Academy of Sciences, 6 Schmiedlstraße, 8042, Graz, Austria 5Institute of marine geology and geophysics Far East Branch of Russian Academy of Sciences, 1B Nauki str., Yuzhno-Sakhalinsk, 693022, Russia Correspondence to: A. Rozhnoi ([email protected]) Received: 31 May 2014 – Revised: 28 October 2014 – Accepted: 31 October 2014 – Published: 4 December 2014 Abstract. The disturbances of very low and low frequency Hayakawa, 2008; Hayakawa et al., 2010; Hayakawa, 2011; signals in the lower mid-latitude ionosphere caused by mag- Biagi et al., 2004, 2007; Rozhnoi et al., 2004, 2009). This netic storms, proton bursts and relativistic electron fluxes band of electromagnetic waves is trapped between the lower are investigated on the basis of VLF–LF measurements ob- ionosphere and the surface of the Earth, and reflected from tained in the Far East and European networks. We have found the boundary between the upper atmosphere and lower iono- that magnetic storm (−150 < Dst < −100 nT) influence is sphere at altitudes of ≈ 70 km (daytime) and ≈ 90 km (night- not strong on variations of VLF–LF signals. The anoma- time). As a result, VLF–LF signals contain important infor- lies with negative amplitude were registered during the main mation about the physical processes in the reflection region and recovery phases for several magnetic storms (mainly for of the ionosphere and its variability. The selection and iden- three northernmost paths). The correlation between VLF– tification of the lower ionosphere perturbations, excited by LF signals and geomagnetic activity is rather weak even seismic activity, tsunamis or volcanic eruptions from other for these paths (≈ 12–18 %). Also, the correlation between possible external sources (e.g., planetary waves, cyclones magnetic activity and VLF signal variations recorded on- and typhoons), are difficult problems. Additionally, to the board the DEMETER satellite is not found. The significant Earth origin disturbances, the ionosphere could be forcing influence of outer-zone particles (energetic particle sensor from above by magnetic storms, solar X-ray flashes, proton on board/Geostationary Operational Environmental Satellite bursts and electron fluxes. The study of the amplitude and (GOES) measurements) on the VLF–LF signal variations is phase of VLF–LF anomalies of non-seismic origin is neces- found for almost half of the sub-ionospheric paths. sary for the reliable identification of seismic anomalies. Keywords. Ionosphere (mid-latitude ionosphere) Previously, VLF phase and amplitude variations and their relationship with geomagnetic activity at mid-latitudes have been studied in the region 10.2–13.6 kHz of the global navigation system “Omega” (see, e.g., Belrose and 1 Introduction Thomas, 1968; Potemra and Rosenberg, 1973; Kikuchi, 1981; Sokolov, 2011). In general, the phase disturbances The measurements of sub-ionospheric very low and low fre- were registered during magnetic storms and the days follow- quency radio signals in the mid-latitude paths in the range ing the recovery of the geomagnetic field. It was found that of 15–50 kHz are broadly used for the identification of earth- quake electromagnetic precursors (see, e.g., Molchanov and Published by Copernicus Publications on behalf of the European Geosciences Union. 1456 A. Rozhnoi et al.: Correlation of very low and low frequency variations at mid-latitudes Figure 2. The same as in Fig.1 but for the European network. The position of the receivers in Moscow (MOS) and Graz (GRZ) and different transmitters in Europe is shown on the map. Sig- nals from six transmitters are analysed: NRK (37.5 kHz), ICV Figure 1. The map of the wave paths in the Far East network. The (20.27 kHz), ITS (45.9 kHz), TBB (26.7 kHz), DHO (23.4 kHz) and location of receivers in Petropavlovsk-Kamchatsky (PTK), Yuzhno- GBZ (19.58 kHz). Sakhalinsk (YSH) and Yuzhno-Kurilsk (YUK) together with the position of the transmitters JJI (22.2 kHz), JJY (40 kHz), NWC (19.8 kHz) and NPM (21.4 kHz) are shown. sub ionospheric VLF–LF signals propagation in various mid- latitude paths for the Far East region and European networks. Besides ground-based observations, the correlation method VLF anomalies can serve as an indirect indicator of energetic is used to analyse the VLF variations recorded onboard the electron injection into the ionosphere. DEMETER satellite. System Omega was terminated in 1997 and therefore in our analysis, we used another navigation, as well as time service transmitters with different frequencies. The appear- 2 Source data ance of anomalies in the VLF–LF signal varies for different wave paths. They strongly depend on path length and its ori- The analysed data were measured by the VLF–LF receivers entation relative to the magnetic field and signal frequency. settled in the Far East and European regions. Their loca- For example, the analysis of the LF signal (40 kHz) vari- tions are shown in Figs.1 and2, correspondingly. Receivers ations registered by the Petropavlovsk-Kamchatsky station have been developed in New Zealand (http://ultramsk.com/) has shown (see, e.g., Rozhnoi et al., 2006): (i) that LF sig- and they are able to provide continuous monitoring of the nal anomalies are typical for the main phase of a magnetic amplitude and phase of MSK (minimum shift key) modu- storm in the night sector; (ii) the similarity of phase and am- lated signals in a frequency range of 10–50 kHz from several plitude anomalies of the LF signal to the structure of the si- VLF–LF transmitters, simultaneously. Each receiver is de- multaneously observed Pi3 geomagnetic pulsations; (iii) the signed to record signals with time resolutions in a range from moderate correlation between Dst index of magnetic activity 50 ms up to 60 s. For the present study, we used 20 s sam- and phase and amplitude anomalies of the LF signal; (iv) the pling frequency measurements obtained from three Far East strong correlation between proton bursts, fluxes of relativis- stations: Petropavlovsk-Kamchatsky (PTK) (53:15◦ N; work tic electrons registered on the board of the GOES satellite since 2000), Yuzhno-Sakhalinsk (YSH) (46:96◦ N; work and characteristics of sub-ionospheric signal. Rozhnoi et al. since 2009) and Yuzhno-Kurilsk (YUK) (44:035◦ N; work (2006) have used another method, which was close to epoch since 2011). The PTK station registers signals from four analysis and gave several examples of case study analysis of transmitters: JJI (22.2 kHz, 32:08◦ N, Japan), JJY (40 kHz, the LF data during electron and proton fluxes. For further 37:37◦ N, Japan), NWC (19.8 kHz, 21:81◦ S, Australia) and investigation of the VLF–LF variations and their relation to NPM (21.4 kHz, 21:42◦ N, Hawaiian Islands). The YSH and the space weather, the existing VLF–LF network was signif- YUK receivers are able to register signals from eight trans- icantly extended in the Far East region and Europe. The new mitters simultaneously. The wave paths from the JJI and JJY receivers were installed in Yuzhno-Sakhalinsk and Yuzhno- transmitters are at mid-latitudes; paths from the NPM trans- Kurilsk (Russia), Graz (Austria) and Sheffield (UK). This mitter are in mid- and low latitudes, and paths from the NWC improvement and the following study are essential for (i) a transmitter are in low and mid-latitudes and cross the Equa- better identification of electromagnetic precursors of earth- tor. Note, these paths are long and cross the regions in which quakes and (ii) for finding the lower ionosphere response to typhoons occur frequently. tsunamis and volcano eruptions. In this work, the case study To study the VLF–LF disturbances in the European re- and correlation analysis are applied for the investigation of gion, we used data from Moscow (MOS) (55:75◦ N; work Ann. Geophys., 32, 1455–1462, 2014 www.ann-geophys.net/32/1455/2014/ A. Rozhnoi et al.: Correlation of very low and low frequency variations at mid-latitudes 1457 Figure 3. An example of the anomalies observed at the amplitude and phase of the JJY (40 kHz) signal recorded in the PTK station during the magnetic storm on 9 March 2012. Three top panels show X-ray, outer-zone protons and electrons (GOES the satellite), and the next panel shows Dst index magnetic activity. In the two bottom panels, the amplitude and phase of the LF signal is shown. Red and black lines are the observed and monthly averaged signals, respectively. The circles highlight the anomalies in the amplitude and phase related to the magnetic storm. since 2009) and Graz (GRZ) (47:065◦ N; work since 2009) used amplitudes of the VLF–LF signals, which do not require stations. These stations can register signals from 12 trans- any additional preprocessing. Due to the complicity of VLF– mitters deployed in Europe, Asia and America. For analy- LF transmitter signal modulation, the phase identification re- sis, we selected the paths passing over seismo-active regions quires special processing. For example, only in one case (see of southern Europe; i.e. the signals from TBB (26.7 kHz, Fig.3) has the phase preprocessing been used to evaluate 37.4◦ N Turkey), ICV (20.27 kHz, 40:92◦ N, Sardinia) and phase anomalies.
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