OBSERVATIONS OF SPACE DEBRIS IN THE VICINITY OF ORBITS OF GLOBAL NAVIGATION SATELLITE SYSTEMS

The problem of the amount and characteristics of space debris in the vicinity of orbits of Global Navigation Satellite Systems (GNSS) is of significant interest from the viewpoint of safe operation of these systems. Attempts have repeatedly been made to search for space debris fragments in a given region of orbits, but have not led to cataloging such objects. Only in 2018, eight space objects were discovered which were not related to active or inactive spacecraft or their launch elements. Photometrical and trajectory observations with optical telescopes are practically the only source of information about characteristics of such objects. The paper presents a summary of the design features and technical characteristics of the new AZT-33VM telescope. We describe a technique for determining orbital parameters of non-cataloged space debris from optical measurements. We report the results of photometric observations of a space object, detected in the vicinity of orbits of the Global Navigation Satellite System GLONASS.

AMPLITUDE VARIATIONS OF THE REFLECTED SIGNAL DURING VERTICAL SOUNDING OF THE IONOSPHERE AT MIDDLE LATITUDES

In this paper, we discuss the main types of quasiperiodic variations in amplitudes of a reflected signal during vertical sounding of the ionosphere at middle latitudes. The initial experimental data is vertical sounding ionograms obtained by the Cyclone ionosonde. The ionosonde is located in Kazan (59°, 49°) and in standard mode allows us to receive one ionogram per minute. In the analysis, methods are used to visualize a large flow of ionograms in the form of final summary maps of the state of the ionosphere (A-, H-, As-maps). We give typical examples of quasiperiodic variations in amplitudes of a reflected signal in ionograms and on A-maps for various types of multipath beatings (polarization and due to signal scattering by ionospheric irregularities). Frequency properties of such beatings are used to estimate the difference in virtual reflection heights between modes of different polarizations with high accuracy, which makes it possible to refine the form of the electron density profile of the lower ionosphere. We have detected a phenomenon rare for the mid-latitude Es layer — beatings of two O modes with different virtual reflection heights. We also present features of quasiperiodic variations in amplitudes of a reflected signal on traces of the transient Es layer. We study possible causes of the appearance of such beatings.

FEATURES OF EXCITATION AND AZIMUTHAL AND MERIDIONAL PROPAGATION OF LONG-PERIOD Pi3 OSCILLATIONS OF THE GEOMAGNETIC FIELD ON DECEMBER 8, 2017

We study the Pi3 pulsations (with a period T=15–30 min) that were recorded on December 8, 2017 at ground stations in the midnight sector of the magnetosphere at the latitude range of DP2 current system convective electrojets. We have found that Pi3 are especially pronounced in the pre-midnight sector with amplitude of up to 300 nT and duration of up to 2.5 hrs. The pulsation amplitude rapidly decreased with decreasing latitude from F′=72° to F′=63°. The event was recorded during the steady magnetospheric convection. In the southward Bz component of the interplanetary magnetic field, irregular oscillations were detected in the Pi3 frequency range. They correspond to slow magnetosonic waves occurring without noticeable variations in the dynamic pressure Pd. Ground-based geomagnetic observations have shown azimuthal propagation of pulsations with a 0.6–10.6 km/s velocity east and west of the midnight meridian. An analysis of the dynamics of pulsations along the meridian has revealed their propagation to the equator at a velocity 0.75–7.87 km/s. In the projection onto the magnetosphere, the velocities are close in magnitude to the observed propagation velocities of substorm injected electrons. In the dawn-side magnetosphere during ground-observed Pi3 pulsations, compression mode oscillations were recorded. We conclude that propagation of geomagnetic field oscillations in this event depends on the dynamics of particle injections under the action of a large-scale electric field of magnetospheric convection, which causes the plasma to move to Earth due to reconnection in the magnetotail. Small-scale oscillations in the magnetosphere were secondary, excited by the solar wind oscillations penetrating into the magnetosphere.

CORONAL JETS AS A CAUSE OF MICROWAVE NEGATIVE BURSTS

We have investigated the cause of three “isolated” negative radio bursts recorded one after another at several frequencies in the 1–17 GHz range at the Nobeyama Radio Observatory, Ussuriysk Astrophysical Observatory, and Learmonth Solar Observatory on April 10–11, 2014. The cause of the rarely observed “isolated” negative bursts is the absorption of radio emission from the quiet Sun’s regions or a radio source in the material of a large eruptive filament. Analysis of observations in different spectral ranges using images from the Nobeyama radioheliograph and the Solar Dynamics Observatory/Atmospheric Imaging Assembly has shown that the cause of all the three radio emission depressions was the screening of the limb radio source by the material of recurrent coronal jets. Parameters of the absorbing material were estimated using a previously developed model. These estimates confirmed the absorption of solar radio emission in cold material with a temperature of ~104 K at the bottom of the jets.

LONG-TERM SOLAR FLUX OBSERVATIONS WITH IRKUTSK INCOHERENT SCATTER RADAR (IISR) IN 2011–2019

Irkutsk incoherent scatter radar (IISR) is an oblongish horn antenna that operates in a meter waveband (154–162 MHz), has a 0.5°×20° beam, and a frequency steering allowing us to tilt the beam by 30° to the south. Besides active measurements of ionospheric conditions and monitoring of space objects, the radar is regularly used for passive radio astronomical observations. From May to August, the Sun crosses the radar field of view and can be in the maximum of the radiation pattern for about two hours. The known shape of the radiation pattern and the high sensitivity of the receiver allow us to conduct calibrated measurements of the solar flux in solar flux units during this period. We have developed a new approach to the calibration, which can be applied to all IISR archival passive data. In the paper, we present long-term observations (2011–2019) of the solar flux in May and summer. We describe the measurement method, present daily average values of the solar flux for this period of passive measurements, and compare it with the solar activity F10.7 index and solar flux measurements made at the Australian observatory Learmonth at 245 MHz. We show that the daily average flux for the period of observations at a frequency of ~161 MHz generally has values from 5 to 10 sfu.

DISTURBED MAGNETOSPHERE ON NOVEMBER 7–8, 2004AND VARIATIONS OF COSMIC RAY CUTOFF RIGIDITY: LATITUDE EFFECTS

We have studied the latitude behavior of cosmic ray cutoff rigidity and their sensitivity to Bz and By components of the interplanetary magnetic field and geomagnetic activity indices Dst and Kp for different phases of the November 7–8, 2004 strong magnetic storm. Cutoff rigidities have been calculated using two methods: the spectrographic global survey method in which the cutoff rigidity is determined from observational data, acquired by the neutron monitor network, and the method in which particle trajectories are calculated numerically in a model magnetic field of the magnetosphere. We have found that the sensitivity of observed cutoff rigidities to Dst changes with latitude (threshold rigidity of stations) is in antiphase with changes in the sensitivity to By. During the recovery phase of the storm, the Dst correlation with By is significantly greater than that with Bz, and the Kp correlation with Bz is greater than that with By. The By component is shown to be a predominant driver of the current systems that determine the Dst evolution during the recovery phase.

MANIFESTATION OF SOLAR ACTIVITY AND DYNAMICS OF THE ATMOSPHERE IN VARIATIONS OF 577.7 AND 630.0 nm ATMOSPHERIC EMISSIONS IN SOLAR CYCLE 24

In the paper, variations of the night emission intensities in the 557.7 and 630 nm atomic oxygen lines [OI] in 2011–2019 have been analyzed. The analysis is based on data from the ISTP SB RAS Geophysical Observatory. The emission intensities are compared with atmospheric, solar, and geophysical parameters. High correlation coefficients between monthly average and annual average 630.0 nm emission intensities and solar activity indices F10.7 have been obtained. This suggests a key role of solar activity in variations of this emission in the period of interest. Variations of the 557.7 nm emission demonstrate to a greater extent the correlations of the stratospheric zonal wind (QBO.U30 index) with quasi-biennial oscillations. The causes of the weak dependence of the 557.7 nm emission intensity on solar activity in solar cycle 24 are discussed.

ANALYZING EXISTING APPLIED MODELS OF THE IONOSPHERE TO CALCULATE RADIO WAVE PROPAGATION AND A POSSIBILITY OF THEIR USE FOR RADAR-TRACKING SYSTEMS. II. DOMESTIC MODELS

We consider the ionospheric models that are suitable for over-the-horizon HF and UHF band radars. Namely, there are three such models: the numerical model developed by IZMIRAN and Fedorov Institute of Applied Geophysics, the numerical model designed by ISTP SB RAS and IDG RAS, and the probabilistic model worked out by IDG RAS. We briefly describe these models and report the results of the analysis of their compliance with radar requirements. Probabilistic models are shown to be most promising; hence, they must be placed at the frontier of ionosphere simulation.

LOW-POWER SOLAR FLARES OF OPTICAL AND X-RAY WAVELENGTHS FOR SOLAR CYCLES 21–24

Using data obtained in optical and X-ray wavelengths, we have analyzed solar flare activity for cycles 21–24. Over the last three cycles, solar activity is shown to decrease significantly. As compared to solar cycle 21 (the most active over the last 50 years), in cycle 24 2–4-class large optical flares are 4.4 times rarer; 1-class flares, 8.2 times; and S-class small flares, 4.1 times. The number of X-class flares decreased 3.7 times; M-class flares, 3.2 times. This confirms that secular solar activity trends affect peak values of 11-year cycles. It is shown that optical low-power flares can be accompanied by proton fluxes and X-ray bursts of different intensity, including X-class ones. Ranges of small flare emission in soft X-rays largely overlap with emission ranges of flares of high optical classes. We have confirmed that X-ray emission from solar flares appears on average 2 min before the optical emission. The X-ray maximum for small optical flares and 1-class flares occurs approximately 1 min later; for 2–4-class flares, 2 min.

FEATURES OF THE INITIAL STAGE OF FORMATION OF FAST CORONAL MASS EJECTION ON FEBRUARY 25, 2014

We have analyzed the fast coronal mass ejection (CME) that occurred on February 25, 2014. The analysis is based on images taken in the 131, 211, 304, and 1700 Å UV channels of the SDO/AIA instrument and from observations obtained in the Hα line (6562.8 Å) with the telescopes of the Teide and Big Bear Observatories. The February 25, 2014 CME is associated with the ejection and subsequent explosive expansion of the magnetic flux rope, which appeared near the solar surface presumably due to the tether-cutting magnetic reconnection. The impulse of full pressure (thermal plus magnetic) resulting from such an “explosion” acts on the overlying coronal arcades, causing them to merge and form an accelerated moving frontal structure of the CME. This pressure impulse also generates a blast collisional shock wave ahead of the CME, whose velocity decreases rapidly with distance. At large distances R>7R₀ (R₀ is the solar radius) from the center of the Sun in front of the CME, a shock wave of another type is formed — a “piston” collisional shock wave whose velocity varies little with distance. At R≥15R₀, there is a transition from a collisional to a collisionless shock wave.