Institute of Cosmophysical Research and Radio Wave Propagation

Abstract. We developed a method and programs for estimation of the global electron content (GEC) from GPS measurements, using the ionosphere models IRI-2001 and NeQuick. During the 23rd cycle of solar activity, the value of GEC varied from 0.8 to 3.2×1032 electrons, following changes in the solar extreme ultra violet (EUV) radiation and solar radio emission at 10.7-cm wavelength. We found a strong resemblance of these variations, with discernible 11-year and 27-day periodicities. A saturation effect of GEC is found when F10.7 increases. We found that GEC is characterized by strong seasonal (semiannual) variations with maximum relative amplitude at about 10% during the rising and falling parts of the solar activity and up to 30% during the period of maximum. It was found that the relative difference between model and experimental GEC series increase as the smoothing time window decreases. We found that GEC-IRI seasonal variations are out-of-phase with experimental GEC values. The lag between model and experimental maximum of GEC values can reach several tens of days. The variations of GEC lag, on average, 2 days after those of F10.7 and UV. GEC completely reflects the dynamics of the active regions on the solar surface. The amplitude of the 27-day GEC variations decreases from 8% at the rising and falling solar activity to 2% at the maximum and at the minimum. We also found that the lifetime of contrast long-living active formations on the Sun's surface in EUV range for more than 1 month exceeds the one in radio range (10.7 cm).

The article is a review of studies of ionospheric effects carried out in ISTP SB RAS. The main results of GPS/GLONASS radio sounding of ionospheric disturbances of natural and anthropogenic origin are presented. The article is devoted to ionospheric effects of solar eclipses, solar flares, solar terminator, earthquakes, tropical cyclones, large-scale ionospheric disturbances of auroral origin, rocket launches. Dynamics of global electron content analysis is also presented. The special attention is paid on the influence of solar flares and ionospheric irregularities on GPS and GLONASS performance. The work is a tribute to the leader of GNSS-monitoring workgroup Prof. E.L. Afraimovich (12 March 1940–8 November 2009).

Abstract Using data of GPS receivers located worldwide, we analyze the quality of GPS performance during four geomagnetic storms of different intensity: two super‐storms and two intense storms. We show that during super‐storms the density of GPS Losses‐of‐Lock (LoL) increases up to 0.25% at L1 frequency and up to 3% at L2 frequency, and up to 0.15% (at L1) and 1% (at L2) during less intense storms. Also, depending on the intensity of the storm time ionospheric disturbances, the total number of total electron content (TEC) slips can exceed from 4 to 40 times the quiet time level. Both GPS LoL and TEC slips occur during abrupt changes of SYM‐H index of geomagnetic activity, i.e., during the main phase of geomagnetic storms and during development of ionospheric storms. The main contribution in the total number of GPS LoL was found to be done by GPS sites located at low and high latitudes, whereas the area of numerous TEC slips seemed to mostly correspond to the boundary of the auroral oval, i.e., region with intensive ionospheric irregularities. Our global maps of TEC slips show where the regions with intense irregularities of electron density occur during geomagnetic storms and will let us in future predict appearance of GPS errors for geomagnetically disturbed conditions.

An empirical model of the quiet daily geomagnetic field variation has been constructed based on geomagnetic data obtained from 21 stations along the 210 Magnetic Meridian of the Circum-pan Pacific Magnetometer Network (CPMN) from 1996 to 2007. Using the least squares fitting method for geomagnetically quiet days (Kp ≤ 2+), the quiet daily geomagnetic field variation at each station was described as a function of solar activity SA, day of year DOY, lunar age LA, and local time LT. After interpolation in latitude, the model can describe solar-activity dependence and seasonal dependence of solar quiet daily variations (S) and lunar quiet daily variations (L). We performed a spherical harmonic analysis (SHA) on these S and L variations to examine average characteristics of the equivalent external current systems. We found three particularly noteworthy results. First, the total current intensity of the S current system is largely controlled by solar activity while its focus position is not significantly affected by solar activity. Second, we found that seasonal variations of the S current intensity exhibit north-south asymmetry; the current intensity of the northern vortex shows a prominent annual variation while the southern vortex shows a clear semi-annual variation as well as annual variation. Thirdly, we found that the total intensity of the L current system changes depending on solar activity and season; seasonal variations of the L current intensity show an enhancement during the December solstice, independent of the level of solar activity.

Abstract. A model of the generation of pulses of local electric fields with characteristic time scales of 1–10 min is considered for atmospheric conditions above fracture regions of earthquakes. In the model, it is proposed that aerosols, increased ionization velocity and upstreaming air flows occur at night-time conditions. The pulses of local electric fields cause respective pulses of infrared emissions. But infrared emissions with time scales of 1–10 min were not observed up to now experimentally. The authors think, that the considered non-stationary field and radiation effects might be a new-type of applicable earthquake indicators and ask to perform special earth-based and satellite observations of the night-time atmosphere in seismoactive fracture regions.

Peculiarities of daytime and nighttime Pi 2 pulsations at the dip equator are examined by using multipoint measurements from the 210° magnetic meridian (MM) magnetometer network. We found that during daytime the amplitude of Pi 2 pulsations at the dip equator is enhanced, and the phase lags ∼ 34° behind those at low‐latitude (magnetic latitude Φ = 19.5‐46.2°) stations. On the other hand, during nighttime the amplitude of Pi 2 pulsations at the dip equator is depressed, and the phase lags ∼ 18° behind those at the lower latitudes. Because the zonal ionospheric conductivity at the dip equator is much higher than that at the off‐dip equator region, Pi 2 signals are expected to be distorted more effectively at the dip equator. The observations imply that the daytime and nighttime Pi 2 pulsations in the equatorial and low‐latitude regions can be explained by invoking an instantaneous penetration of electric field variations from the nightside polar ionosphere to the dayside equatorial ionosphere, and a direct incidence of compressional oscillations from the nightside inner magnetosphere, respectively.

Abstract. One hundred three cases of a bay-like depression in the strength of the Ez component of the quasistatic electric field in the near-Earth atmosphere, observed from 1997 to 2002 on Kamchatka, have been analyzed statistically. It has been shown that the most probable length of a bay is 40–60 min. The most probable drops in Ez are minus 106–300 V/m. The dependence of these values on an earthquake class and a distance to the epicenter was not found. The probability of earthquake prediction over 24 h before an earthquake based on the Ez anomaly is 36%.

Abstract. The non-stationary Frenkel model of the generator of spikes of the local electric field with time scales of 1–100 min in the atmosphere near seismic fracture regions some days before strong earthqukes is analysed. The model suggests an aerosol cloud, an increased ionisation velocity (e.g. by radon emanation), and an upward flow of air. It was found that during times of earthquake activity (that means a few days before an earthquake), for realistic increases of the ionization intensity of the atmosphere, mosaic-likely occurring and disappearing pulses of local electric fields with intensities of the order of 103−3×103 Vm−1 should be observable. These electric fields would also cause spikes of non-equilibrium IR emissions (0.7–20 μm) and local spikes of the magnetic field. The authors propose to perform special complex Earth-based observations of the night-time emissions of the atmosphere in the IR region and of the magnetic as well as quasi-stationary electric fields at some points near to fracture regions in seismo-active belts.

Abstract This study investigates the impact of dynamical processes in the neutral atmosphere on the high-midlatitude ionosphere during two sudden stratospheric warming (SSW) events. For this purpose, the reanalysis meteorological data of the National Centers for Environmental Prediction / National Center for Atmospheric Research (NCEP/NCAR) and UK Met Office (UKMO) were used in addition to that from the high-midlatitude chain of Russian ionosonde stations. The results show that the ionospheric response to the SSW events at high-midlatitudes depends on the position of the ionosonde stations relative to the stratospheric circulation pattern. Two well-pronounced effects were detected in this study. The first effect, observed in January 2009, was a negative effect in critical frequency (f o F2) and a positive effect in F2 layer maximum (h m F2) above the border of a stratospheric cyclone and an anticyclone with northward flow direction. During a 6-day period, the ionosphere exhibited a sharply inhomogeneous longitudinal structure when ionosondes, displaced at a longitude of approximately 20°, showed differences of approximately 1 MHz in f o F2 and more than 50 km in h m F2. The second feature, which was clearly observed in January 2013, implied a positive effect in f o F2 up to approximately 2.5 MHz and a negative effect in h m F2 at approximately 10 km above the center of the stratospheric cyclone. We conclude that these effects were caused by upward transport of molecular gas to the lower thermosphere for the first case and a pulldown forcing of molecular species above the low-pressure zone inside the cyclone for the second case. Changes in the O + /N 2 ratio in the lower thermosphere altered the O + recombination rate and the corresponding variations of ionosphere parameters.

A hybrid model for the time series of complex structure (HMTS) was proposed. It is based on the combination of function expansions in a wavelet series with ARIMA models. HMTS has regular and anomalous components. The time series components, obtained after expansion, have a simpler structure that makes it possible to identify the ARIMA model if the components are stationary. This allows us to obtain a more accurate ARIMA model for a time series of complicated structure and to extend the area for application. To identify the HMTS anomalous component, threshold functions are applied. This paper describes a technique to identify HMTS and proposes operations to detect anomalies. With the example of an ionospheric parameter time series, we show the HMTS efficiency, describe the results and their application in detecting ionospheric anomalies. The HMTS was compared with the nonlinear autoregression neural network NARX, which confirmed HMTS efficiency.

Abstract. Using TEC measurements from the dense network of GPS sites GEONET, we have obtained the first GPS-TEC image of the space structure of medium-scale traveling wave packets (MS TWP) excited by the morning solar terminator (ST). We found that ST-generated wave packets have duration of about 1–2 h and time shift of about 1.5–6 h after the morning ST appearance at an altitude of 300 km. The TWP wave front extends along the morning ST line with the angular shift of about 20°. The time period and wave-length of ST-generated wave packets are about 10–20 min and 200–300 km, respectively. The velocity of the TWP phase front traveling is of about 300 m/s. The space image of MS TWP manifests itself in pronounced anisotropy and high coherence over a long distance of about 2000 km.

In the present paper, we propose a wavelet-based method of describing variations in the Earth’s magnetic field, such as the horizontal component of the geomagnetic field, in addition to methods for evaluating changes in the energy characteristics of the field and for isolating the periods of increased geomagnetic activity. Based on a combination of multiresolution wavelet decompositions with neural networks, we propose a method of approximation of the cosmic ray time course and the allocation of anomalous variations (Forbush effects) that occur during periods of high solar activity. During the realization of the method, an algorithm was created for selecting the level of the wavelet decomposition and adaptive construction of the neural network. By using the proposed methods, we performed a joint analysis of the geomagnetic field and cosmic rays during periods of strong magnetic storms. The strongest geomagnetic field perturbations were observed in periods of abnormal changes in cosmic ray level. Assessment of the intensity of geomagnetic disturbances on the eve of and during magnetic storm development allowed us to highlight local increases in intensity of the geomagnetic field occurring at different frequency ranges prior to the development of the storm’s main phase. Implementation of the proposed method with theoretical tools in combination with other methods will improve the estimation accuracy of the geomagnetic field state during space weather forecasting.

We reexamined the daily S q ‐equatorial electrojet (EEJ) relationship based on these extended magnetometer networks in the east Asian region: (1) the Circum‐pan Pacific Magnetometer Network (CPMN), (2) the International Real‐time Magnetic Observatory Network (INTERMAGNET), and (3) the World Data Center for Geomagnetism, Kyoto (WDC). Daily variations of the geomagnetic field for geomagnetically quiet days (Kp ≤ 2+) from 1996 to 2005 were analyzed. Noontime eastward S q current intensities were estimated by latitudinally integrating the north‐south component of the S q field. The corresponding EEJ intensities were estimated from the daily geomagnetic field variations observed at Davao station (dip latitude of −0.84°deg). We discovered that these intensities of daily S q and EEJ are well correlated on a long‐term basis ( r = 0.80). The dependences on the solar activity (as indicated by F 10.7) and season (the day number) of S q and EEJ variations were examined. It was demonstrated that both daily S q and EEJ intensities are correlated to F 10.7 with similar sensitivities. F 10.7 is known to show similar variations with solar EUV radiation which causes ionization and heating of the ionosphere. For seasonal dependence, both daily S q and EEJ intensities show predominant semiannual variations with similar spring‐fall asymmetry. The effect of seasonal changes of the EUV flux into the low‐latitude ionosphere is considered. Our results indicate that the daily values of S q and EEJ react, in the same manner, to temporal changes of solar ionization and heating of the ionosphere.

The Solar-Terrestrial Environment Laboratory (STEL) induction magnetometer network has been developed to investigate the propagation characteristics of high-frequency geomagnetic pulsations in the Pc1 frequency range (0.2–5 Hz). Five induction magnetometers were installed in the period 2005–2008 at Athabasca in Canada, Magadan and Paratunka in Far East Russia, and Moshiri and Sata in Japan. The sensitivity of these magnetometers is between 0.3 and 13 V/nT at turnover frequencies of 1.7–5.5 Hz. GPS time pulses are used for accurate triggering of the 64-Hz data sampling. We show examples of PiB/Pc1 magnetic pulsations observed at these five stations, as well as the harmonic structure of ionospheric Alfvén resonators observed at Moshiri. We found that the Pc1 packets are slightly modulated as they propagate from high to low latitudes in the ionospheric duct. These network observations are expected to contribute to our understanding of Pc1-range magnetic pulsations and their interaction with relativistic electrons by combining the obtained results with future satellite missions that observe radiation belt particles.

To investigate the generation and propagation mechanisms of Pi 2 magnetic pulsations, we have analyzed magnetic field data from the 210° magnetic meridian (MM) stations. We used 50 Pi 2 events that were simultaneously observed at seven stations along the 210° MM during January 1995, and focused our analysis on associated magnetic energy, ((Δ H )²+(Δ D )²)/µ 0 . The times when the amplitude of the magnetic energy attained the maximum ( T max ) were compared among these stations. We found that T max has a latitudinal dependence, especially at higher latitudes, which has not been previously reported. At Kotel'nyy (L=8.50) on the poleward side of the auroral region, T max occurred an average of 21 seconds earlier than T max at Guam (L=1.01), and often as much as one minute earlier. The existence of latitudinal variation has implications for interpretation of issues related to timing of substorm onset; it is necessary to consider the global features of Pi 2 events in the study of auroral and magnetospheric substorms.

The total electron content (TEC) data obtained by the GPS network and GPS radio interferometry methods developed by the authors has made it possible to determine the spatial structure and dynamics parameters of large‐scale traveling ionospheric disturbances (LS TID) generated during the strong magnetic storm on 29 October 2003. It was shown that the LS TID registered in the auroral zone after a sudden storm commencement (SSC) represented a large‐scale solitary type wave with an annular front shape whose center was located near the geomagnetic pole. The wave had a period of about 40–60 min and traveled up to 4500 km equatorward. The relative amplitude of the LS TID was 5–10%. Comparison with ionosonde data has shown that this value corresponds to the relative amplitude of electron density disturbance in the F layer maximum of about 45–50%. The velocity and travel direction of the LS TID had a strongly pronounced longitudinal dependence. A “swirling” effect was detected in the LS TID movement, the direction of which was opposite to the Earth's rotation. The westward directed zonal projection of LS TID velocity caused this “swirling” effect. In the morning and evening sectors the zonal projection exceeded the meridional one. The diurnal movement of the ionization maximum may influence the zonal transfer of LS TID.

The results of geoacoustic emission investigations carried out on the seismoactive Kamchatka Peninsula since 1999 are presented. The experiments are characterized by the application of broadband piezoceramic sound receivers (hydrophones) for recording the emission. The hydrophones were installed at the bottom of natural and artificial water reservoirs. As compared with the standard hydrophones, such receivers allow us to broaden the registration frequency range up to 0.1 Hz–11 kHz. Three-component vector receivers with the same frequency range were used simultaneously to study the spatial structure of the geoacoustic emission and the mode of the medium particle movement in a wave. In the course of the investigations, it was established that anomalies of the geoacoustic emission in the kilohertz frequency range are recorded 1–3 days before strong earthquakes at a distance of a few hundred kilometers from the epicenter. A sharp increase in the amplitude and frequency of the geoacoustic impulses, which resemble microearthquakes in pattern and last from tens of minutes to several hours, is interpreted as an anomaly. Signals at such frequencies cannot propagate from the epicenters of preparing earthquakes and represent the response of the medium at the registration point to the change of its stress-strain state. The stress field created therein determines the primary orientation of the emission sources, which can be assessed by vector-phase methods. The results of the integrated investigations of the geoacoustic emission and the Earth’s surface deformation revealed that anomalies are observed before earthquakes with a considerable increase in the strain rate during both the compression and extension of the near-surface rocks.

In this study, a new multicomponent model (MCM) to determine the time variation of ionospheric parameters is suggested. The model was based on the combination of wavelets with autoregressive-integrated moving average model classes and allowed the study of the seasonal and diurnal variations of ionospheric parameters and the determination of anomalies occurring during ionospheric disturbances. To investigate in detail anomalous changes in the ionosphere, new computational solutions to detect anomalies of different scales and estimate their parameters (e.g., time of occurrence, duration, scale, and intensity) were developed based on a continuous wavelet transform. The MCM construction for different seasons and periods of solar activity was described using ionosphere critical frequency f o F2 data from Kamchatka (Paratunka Station, 52° 58′ N, 158° 15′ E, Institute of Cosmophysical Research and Radio Wave Propagation FEB RAS). A comparison of the MCM with the empiric International Reference Ionosphere (IRI) model and the moving median method for the analyzed region showed that the suggested method was promising for future research, since it had the advantage of providing quantitative estimates for the occurrence time, duration, and intensity of the anomalies, characterizing the ionospheric state and disturbance degree with a higher accuracy. Geomagnetic storms from 17 March and 2 October 2013 were analyzed using the suggested method, and it was shown that the ionospheric disturbances were at maximum during the strongest geomagnetic disturbances. An increase in the electron concentration in comparison with the background level, under calm or weakly disturbed geomagnetic field conditions, was identified before the analyzed magnetic storms.

In order to clarify the correlation of high- and low-latitude Pi 2 magnetic pulsations, we have analyzed 1-s magnetic data from the Chokurdakh (Φ =64.75°, L = 5.50), Magadan (Φ= 53.70°, L =2.85), and Moshiri (Φ = 37.76°, L = 1.60) stations along the 210° magnetic meridian. The H-component Pi 2 amplitudes are of almost the same order in the plasmasphere. In the outside region of the plasmapause the H-component amplitudes become roughly 1 order larger than those of in the plasmasphere. The D-component amplitudes, on the other hand, increase exponentially from lower to higher latitudes. At L = 1.60-2.85 the H- and D-component Pi 2 amplitudes show in-phase relation. Between L = 2.85 and 5.50, the Hcomponents have a roughly out-of-phase relation, while the D components show an unclear relation. These observations suggest that Pi 2 pulsations consist of several different modes in the structured magnetosphere.

In this work, based on Newton’s second law, taking into account heredity, an equation is derived for a linear hereditary oscillator (LHO). Then, by choosing a power-law memory function, the transition to a model equation with Gerasimov–Caputo fractional derivatives is carried out. For the resulting model equation, local initial conditions are set (the Cauchy problem). Numerical methods for solving the Cauchy problem using an explicit non-local finite-difference scheme (ENFDS) and the Adams–Bashforth–Moulton (ABM) method are considered. An analysis of the errors of the methods is carried out on specific test examples. It is shown that the ABM method is more accurate and converges faster to an exact solution than the ENFDS method. Forced oscillations of linear fractional oscillators (LFO) are investigated. Using the ABM method, the amplitude–frequency characteristics (AFC) were constructed, which were compared with the AFC obtained by the analytical formula. The Q-factor of the LFO is investigated. It is shown that the orders of fractional derivatives are responsible for the intensity of energy dissipation in fractional vibrational systems. Specific mathematical models of LFOs are considered: a fractional analogue of the harmonic oscillator, fractional oscillators of Mathieu and Airy. Oscillograms and phase trajectories were constructed using the ABM method for various values of the parameters included in the model equation. The interpretation of the simulation results is carried out.