Sounding of HF heating-induced artificial ionospheric disturbances by navigational satellites radio transmissions.

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1 Sounding of HF heating-induced artificial ionospheric disturbances by navigational satellites radio transmissions. V.E. Kunitsyn 1, E.S. Andreeva 1, V.L. Frolov, G.P. Komrakov, M.O. Nazarenko 1, A.M. Padokhin 1 1 M.V. Lomonosov Moscow State University, Moscow, Russia Radiophysical Research Institute, N. Novgorod, Russia Abstract In this work we report on the results of the ionospheric heating experiments, which were carried out at the Sura facility (Radiophysical Research Institute, N. Novgorod, Russia) during several heating campaigns in 009 and 010. We present experimental evidences for the influence of the electron density perturbations, induced by HF-heating in the midlatitude ionosphere, on the GNSS radio signals. Variations in the total electron content (TEC), proportional to the reduced phases of navigational signals, were studied. Examples of the identification of the heating-induced variations in TEC, including determination of the amplitudes and temporal characteristics are presented. We also present and discuss examples of the amplitude scintillations of the beacon signals from low orbital (LO) navigational satellites (Parus/TRANSIT) and corresponding TEC perturbations caused by heating as well as tomographic crossections of the heated area. 1. Introduction Numerous studies of the influence of powerful HF radio waves on the ionospheric plasma [1-3] showed the development of ponderomotive parametric, thermal (resonant) parametric and selffocusing instabilities near the reflection height of the powerful radio wave, which leads, in particular, to the strong electron heating of ionospheric plasma in this region and to the generation of artificial irregularities in the ionospheric electron density with the scale sizes from fractions of meter to dozens of kilometers [1]. These irregularities have a considerable effect on the VHF/UHF/L-band radio waves propagating through the heated area of the ionosphere and can be sounded by the signals of GNSS and LO navigational systems, operating in those bands[1,4-7]. In this paper, we analyze the experimental results of the influence of electron density perturbations produced by the highfrequency heating of the ionosphere at the Sura facility on the GNSS and LO navigational signals.. Description of the experiments and processing scheme The experiments were carried out at the Sura heating facility (56.15N, 46.1E) during several heating campaigns. The measurements were conducted when fof>f (here f is the heater frequency and fof is a critical frequency of the F layer, which was monitored by the Sura ionospheric station). We also predicted satellite trajectories and carried out our experiments when the ionospheric penetration points, calculated at the reflection height of the HF pump wave, of one or more GNSS or LO navigational satellites crossed the heated area. In order to increase the efficiency of excitation of the artificial ionospheric turbulence using the magnetic zenith effect [1,5], the antenna beam was inclined by 1 0 from vertical to the south in the plane of the geomagnetic meridian. The scheme of the experiments is presented in Fig. 1. HF pump wave with O-mode polarization radiated with different heating schemes: 30 s heating with maximum effective radiated power followed by 30 s pause (or, in brief notation, ±30 s); ±3 min; ±5 min; ±6 min; ±10 min; +10 min -5 min. The half-power beam width for the Sura facility is ~1 O, ionospheric penetration points of slowly moving GNSS satellites could remain within the heated area for min, which allows to obtain some information about the temporal characteristics of the heater-induced ionospheric disturbances. From the other hand, signals from the rapidly moving LO satellites could provide us with almost momentum snapshot of the heated area.

2 GNSS or LO navigational satellite 0:30 UT 08:03 UT to magnetic zenith h ~ 00km reflection height of pumping wave Reflection when ~1 0 f 0 <f 0 F ω L = Heated area d~70 km 4πe N(h) m 1/ 4πe N(h) ω UH = +ω H m 1/ 1:3 UT receiver Sura heater 07:15 UT Figure 1. Scheme of the experiments and trajectories of ionospheric penetration points. For our experiments at the Sura facility we specially installed dual frequency GNSS receiver near the facility. GNSS satellite radio transmissions were recorded with 10 Hz sampling. Both L1 and L GNSS carrier phases were used in the analysis for calculating the relative slant total electron content (stec): stec = + const K = c = L 3 1 L f1 f c 8, where m, 3 10 m f1 f s f1 f K. (1) s The time series of stec were then detrended and TEC variations during the heating sessions (vartec) were analyzed using the wavelet transform to estimate the local energy spectra of these variations: N 1 1 t N * k b j 1 tk bj Sa ( i, bj) = Wa ( i, bj) ; Wa ( i, bj) = var TECt ( k) ψ / exp, k= 0 ai k= 0 a i () where N is a number of counts in TEC record, a i is the analogue of the period, b j is the analogue of time, ψ () t = exp ( t /) exp( iπ t) is the Morlet mother wavelet function, with the aim to reveal the frequency components and their timing to be compared with the modes of the Sura facility operation. We also used two beacon receivers for LO satellites, one was installed at the site of the Sura facility, another one ~100 km to the north at Galibikha village. This allowed us to investigate large scale ionospheric irregularities caused by heating using ray tomography approach, in which the measured reduced phase φ of probing beacon signals, to an accuracy of the unknown initial phase ϕ 0, is proportional to the TEC along the ray from satellite to the receiver: φ+ ϕ Ndl, where N e is electron density and dl is ray element, (3) 0 e and tomographic inversion of φ measurements from a chain of receivers gives the electron density distribution in the vertical plane above the receivers [8]. We also studied small-scale irregularities of electron density, which in contrast to large-scale irregularities, mainly affect the amplitude scintillations of the LO beacon [Tereshenko]. If the disturbed ionosphere contains a layer of anisotropic small-scale irregularities, which properties are

3 described by the variance of electron density σ N, the field-aligned anisotropy parameter α, the field-perpendicular anisotropy parameter β, the orientation angle Ψ of the anisotropy in the plane perpendicular to the geomagnetic field, and the spectrum of the fluctuations is assumed to obey the power law with power index p, the variance of the logarithmic relative amplitude of the beacon signal χ = ln( A/ A0 ), where A0 is the amplitude in the absence of irregularities, reads: [ ] σ χ σn( z) f RF( z), α, β, Ψ, p, Θ( z) dz. (4) Here R F is Fresnel radius, Θ is the angle between geomagnetic field and the ray from the satellite to the receiver, the integration is taken in the limits of the layer of irregularities and the function f is introduced by [9]. Instead of χ the experiments we can obtain % χ = ln( A/ A ), where A is mean amplitude of the signal, but since σ χ = σ % χ the experimental and theoretical variances can be compared to estimate parameters of small-scale irregularities [9, 10]. 3. Obtained results Results presented in Fig. are from experiments at Sura facility. Left panels are slant TECs and TEC variations, right panels are the corresponding wavelet spectra of TEC variations for the satellites which ionospheric penetration points crossed the heated area during heating experiments. The first two results (Fig..a,b) were obtained in daytime, the last one (Fig..c) in nighttime conditions. In the first part of the experiment shown in Fig.1.a the Sura facility operated with ±30 s mode with the effective radiated power of 40 MW until 7:36 UT and 80 MW later. From 7:51 UT till 8:6 UT Sura heater started operating in ±5 min mode with the effective radiated power of 80 MW. The 1 min periodical component corresponding to the period of PW modulation is apparent in the plot of TEC variations and in the local spectrum of TEC variations, but only for the period, when the facility operated with the effective radiated power of 80 MW. The 1 min periodical component vanishes together with termination of ±30 s mode of operation. This is an evident indication of the artificial nature of the observed variations as well as of the fact that under given ionospheric conditions, the effective radiated power of 40 MW with ±30 s mode of heating was insufficient to generate the disturbances in the electron density, detectable in GNSS data. Harmonics of the main PW modulation frequency were also observed in the wavelet spectra of TEC variations in a number of our other experiments (Fig 1. b, c). Maximum TEC variations were observed in the area near the magnetic zenith. We observed in TEC variations not only harmonic components, which are present in the spectrum of the pumping wave modulation (for example in Fig.b for the heating mode +10 min. -5 min we observed first (15 min) and second (7.5 min) harmonics in TEC variations, which are also present in the spectrum of PW modulation), but also harmonic components which are absent in the spectrum of PW modulation (for example in Fig.c second harmonic (6 min.) in the spectrum of TEC variations, which is absent in the spectrum of PW modulation for the ±6 min. mode of heating; this second harmonic can be explained by the quadratic dependence of the electron temperature perturbations from the electric field of the powerful radiowave). Note also that amplitudes of TEC variations caused by heating were greater in nighttime conditions than in daytime conditions even though the effective radiated power for the nighttime experiments was sometimes lower. It should be mentioned that under daytime conditions, contrary to the nighttime conditions, a typical TEC behavior is the increase in its value when PW switches-on (see Fig. 1a,b). As it was stated in [7], such TEC behavior is determined by plasma density growth at heights of about of km when the ionosphere is pumped by powerful HF waves. We can also estimate the electron density perturbation δ N at the reflection height of the heating wave using

simple relation: δn N δtec lf e, (5) 0F πm e where e and me are electron charge and mass, N is electron density at the reflection height of heating wave, approximately corresponding to the critical

conditions b) O-mode, f=4.3mhz, ERP~80MW, 1 0 from vertical to the south in the plane of the geomagnetic meridian; quiet geomagnetic conditions c) O-mode, f=4.

4 simple relation: δn N δtec lf e, (5) 0F πm e where e and me are electron charge and mass, N is electron density at the reflection height of heating wave, approximately corresponding to the critical frequency f0f, δtec - heating induced TEC variations. Assuming the thickness of the disturbed region l does not exceed 5-15 km, we obtain the perturbations about 10%, which is rather significant. a) O-mode, f=4.3mhz, ERP~40MW until 7:36UT and 80MW after that, beam inclined by 1 0 from vertical to the south in the plane of the geomagnetic meridian to use magnetic zenith effect [1]; quiet geomagnetic conditions b) O-mode, f=4.3mhz, ERP~80MW, 1 0 from vertical to the south in the plane of the geomagnetic meridian; quiet geomagnetic conditions c) O-mode, f=4.3mhz, ERP~60MW, 1 0 from vertical to the south in the plane of the geomagnetic meridian; moderate geomagnetic conditions Figure. Heating results from the Sura facility. Variations of slant TEC (left panels) and local spectra of TEC variations (right panels) for GPS satellites, which ionospheric penetration points crossed the heated area. Borders of heated area are indicated by arrows, heating pulses are indicated with red rectangles.

We also studied the heated area by ionospheric radiotomography (for large scale irregularities) and amplitude scintillation methods (for small scale irregularities) receiving signals of LO

3 we present phase measurements and corresponding tomographic cross section of ionosphere with a trough and a wavelike structures in the heated area. In Fig.

5 We also studied the heated area by ionospheric radiotomography (for large scale irregularities) and amplitude scintillation methods (for small scale irregularities) receiving signals of LO navigational satellites. In Fig. 3 we present phase measurements and corresponding tomographic cross section of ionosphere with a trough and a wavelike structures in the heated area. In Fig. 4 we present the variance of the logarithmic relative amplitude of the signal at one of the receiving stations during the same satellite pass and its model fit according to (4), with its maximum at the magnetic zenith of the station. The estimated ratio of the axes of small-scale irregularities, corresponding to this peak is 35(along magnetic field):7:1, the orientation of perpendicular anisotropy is eastward from geomagnetic north. Figure 3. TEC measurements at two stations, LO satellite pass and tomographic reconstruction of the heated area Figure 4. Study of amplitude scintillations caused by heating. Logarithmic relative amplitude (gray line) of the beacon signal at Galibikha receiving station and its model fit (black line).

6 4. Conclusion This work demonstrates the possibilities of combined GNSS measurements and LO tomographic and scintillations studies in connection with ionospheric heating. GNSS measurements can successfully reveal temporal variations of electron density in heated area, while LO tomography provides information about large scale irregularities, and scintillation studies about small scale irregularities. Acknowledgments The authors are grateful to the Sura staff for the help in experiments and acknowledge support of Russian Foundation for Basic Research (grants nos , , ) and Russian Ministry of Science and Education (contracts P167, P107 and ) References 1. Gurevich, A.V. Nonlinear effects in the ionosphere. Phys. Usp. 50, , Frolov, V.L., Bakhmet eva, N.V., Belikovich, V.V., Vertogradov, G.G., Vertogradov, V.G., Komrakov, G.P., Kotik, D.S., Mityakov, N.A., Polyakov, S.V., Rapoport, V.O., Sergeev, E.N., Tereshchenko, E.D., Tolmacheva, A.V., Uryadov, V.P., Khudukon, B.Z. Modification of the earth s ionosphere by high-power high-frequency radio waves. Phys. Usp. 50, , Frolov, V.L., Erukhimov, L.M., Metelev, S.A., Sergeev, E.N. Temporal behaviour of artificial small-scale ionospheric irregularities: review of experimental results. J. Atmos. Solar Terr. Phys. 59 (18), , Milikh, G., Gurevich, A., Zybin, K., Secan, J. Perturbations of GPS signals by the ionospheric irregularities generated due to HF-heating at triple of electron gyrofrequency. Geophys. Res. Lett. 35, L10, Tereshchenko, E.D., Milichenko, A.N., Frolov, V.L., Yurik, R.Y. Observations of the magneticzenith effect using GPS/GLONASS satellite signals. Radiophys. Quant. Electron. 51 (1), , Kunitsyn, V.E., Padokhin, A.M., Vasiliev, A.E., Kurbatov, G.A., Frolov, V.L., Komrakov, G.P. Study of GNSS-measured ionospheric total electron content variations generated by powerful HFheating. Adv. Space Res., 011. Vol. 47(10), pp V. L. Frolov, G. P. Komrakov, V. E. Kunitsyn, A. M. Padokhin, A. E. Vasiliev and G. A. Kurbatov Sounding of the ionosphere disturbed by the Sura heating facility radiation using signals of the GPS satellites. Radiophys. Quant. Electron. 53(7), , Kunitsyn V.E. and Tereshchenko E.D. Ionospheric Tomography. -New York: Springer-Verlag p. 9. E. D. Tereshchenko, B. Z. Khudukon, M. O. Kozlova, O. V. Evstafiev, T. Nygrén, M. T. Rietveld, and A. Brekke // Comparison of the orientation of small-scale electron density irregularities and F region plasma flow direction. Ann. Geophys., 18, , E. D. Tereshchenko, M. O. Kozlova, O. V. Evstafiev, B. Z. Khudukon, T. Nygrén, M. Rietveld, and A. Brekke // Irregular structures of the F layer at high latitudes during ionospheric heating Ann. Geophys., 18, , 000

Radiotomographic imaging of the artificially disturbed midlatitude ionosphere with CASSIOPE and Parus satellites

Radiotomographic imaging of the artificially disturbed midlatitude ionosphere with CASSIOPE and Parus satellites Vyacheslav E. Kunitsyn 1, Elena S. Andreeva 1, Artem M. Padokhin 1, Vladimir L. Frolov 2,