Institute Of Solar-Terrestrial Physics Research Articles

Iceland spar and birefringent filter (BF) development

Birefringent crystals for BF are required to provide the necessary linear aperture, wavefront quality, and filter transmission in a given spectral region. Based on the review of foreign and domestic BF developments, the difficulties in using crystals from known deposits are examined. The Institute of Solar-Terrestrial Physics has developed BFs with extreme characteristics, using an innovative method for enriching crystals from East Siberian deposits and new methods for optical treatment and control of BF elements. We present the characteristics of the filters. Further progress in the creation of BFs in our country depends on the availability of necessary synthetic crystals and natural crystal of Iceland spar, which turned out to be a difficult fate in Russia.

Исландский шпат и разработка интерференционно-поляризационных фильтров (ИПФ)

Birefringent crystals for BF are required to provide the necessary linear aperture, wavefront quality, and filter transmission in a given spectral region. Based on the review of foreign and domestic BF developments, the difficulties in using crystals from known deposits are examined. The Institute of Solar-Terrestrial Physics has developed BFs with extreme characteristics, using an innovative method for enriching crystals from East Siberian deposits and new methods for optical treatment and control of BF elements. We present the characteristics of the filters. Further progress in the creation of BFs in our country depends on the availability of necessary synthetic crystals and natural crystal of Iceland spar, which turned out to be a difficult fate in Russia.

New Active Galactic Nuclei Detected by the ART-XС and eROSITA Telescopes Onboard the SRG Observatory during an All-Sky X-ray Survey

We present the results of our identification of 17 X-ray sources detected in the 4-12 keV energy range by the Mikhail Pavlinsky ART-XC telescope during the first year of the SRG all-sky survey. Three of them have been discovered by the ART-XC telescopes, while the remaining ones have already been known previously as X-ray sources, but their nature has remained unknown. We took optical spectra for nine sources located in the northern sky $\delta > -20$ deg with the 1.6-m AZT-33IK telescope at the Sayan Observatory (the Institute of Solar-Terrestrial Physics, the Siberian Branch of the Russian Academy of Sciences) and the 1.5-m Russian-Turkish telescope at the TUBITAK National Observatory. For the remaining objects we have analyzed the archival optical spectra taken during the 6dF survey. All of the investigated objects have turned out to be Seyfert galaxies (eight of type 1, seven of type 2, and two of intermediate type 1.8) at redshifts up to $z\approx 0.15$. Based on data from the eROSITA and ART-XC telescopes onboard the SRG observatory, we have obtained X-ray spectra in the energy range 0.2-20 keV for eight sources. A significant intrinsic absorption ($N_H > 10^{22}$ cm$^{-2}$) has been detected in three of them, with two of them being probably strongly absorbed ($N_H \sim 10^{23}$ cm$^{-2}$). This paper is a continuation of the series of publications on the optical identification of active galactic nuclei detected by the ART-XC telescope.

Estimated influence of stratospheric activity on the ionosphere according to measurements with ISTP SB RAS tools

We present the results of a comprehensive study of the manifestation of wave activity with periods of internal gravity waves (IGW) in various regions of the atmosphere: in the stratosphere, upper mesosphere, and in the F2-region of the ionosphere. The study is based on radiophysical and spectrometric measurements made with tools of the Institute of Solar-Terrestrial Physics (ISTP) SB RAS and the Era-Interim reanalysis data. The correlation coefficient with time shift between ionospheric and stratospheric activity for the annual interval varies in the range from 0.45 to 0.54, and for the 27-day interval it reaches the levels 0.4–0.8 in seventy percent of the cases. Thirty percent of correlation coefficients less than 0.4 can be explained by the influence of neutral wind, geomagnetic activity, and non-stratospheric IGW sources. Comparison between stratospheric activity and variations in characteristics of traveling ionospheric disturbances (TID) has shown that a ~15 day shift in stratospheric activity results in a fairly high correlation between stratospheric activity and disturbance of IGW characteristics (~0.6). The delay of about 15 days can be attributed to the delay in the temperature variations at heights of the lower thermosphere relative to the temperature variations at the altitude pressure level of 1 hPa. Comparative analysis of variations in mesospheric and ionospheric activity has revealed time intervals when their behavior is consistent.

Оценка влияния стратосферной активности на ионосферу по данным измерений на комплексе инструментов ИСЗФ СО РАН

We present the results of a comprehensive study of the manifestation of wave activity with periods of internal gravity waves (IGW) in various regions of the atmosphere: in the stratosphere, upper mesosphere, and in the F2-region of the ionosphere. The study is based on radiophysical and spectrometric measurements made with tools of the Institute of Solar-Terrestrial Physics (ISTP) SB RAS and the Era-Interim reanalysis data. The correlation coefficient with time shift between ionospheric and stratospheric activity for the annual interval varies in the range from 0.45 to 0.54, and for the 27-day interval it reaches the levels 0.4–0.8 in seventy percent of the cases. Thirty percent of correlation coefficients less than 0.4 can be explained by the influence of neutral wind, geomagnetic activity, and non-stratospheric IGW sources. Comparison between stratospheric activity and variations in characteristics of traveling ionospheric disturbances (TID) has shown that a ~15 day shift in stratospheric activity results in a fairly high correlation between stratospheric activity and disturbance of IGW characteristics (~0.6). The delay of about 15 days can be attributed to the delay in the temperature variations at heights of the lower thermosphere relative to the temperature variations at the altitude pressure level of 1 hPa. Comparative analysis of variations in mesospheric and ionospheric activity has revealed time intervals when their behavior is consistent.

Irkutsk Incoherent Scatter Radar: history, present and future

Abstract. The article focuses on the history of ionospheric research using the incoherent scatter method at the Institute of Solar-Terrestrial Physics and development of the only incoherent scatter radar in Russia, which is located near Irkutsk. It describes the radar features and the current situation of research at the Irkutsk Incoherent Scatter Radar (IISR). Operating modes and types of measurements of the radar are specified. There is a brief description of the original measurement techniques that were developed considering the IISR features such as the frequency principle of scanning and receiving of one linear polarization of a scattered signal. The main feature of the IISR is the possibility of obtaining absolute values of the ionospheric plasma electron density. The automatic method for constructing the electron density vertical profile is based on registration of vertical profiles of a rotation phase of the polarization plane of a scattered signal. The method does not require calibration with additional facilities.

Effect of Atmospheric Aerosol on Ground-Based Airglow Observations

We study how the atmospheric aerosol influences the recorded emission of the Earth’s upper atmosphere. The study was performed using the data from an automatic CIMEL CE-318 sun photometer, a part of the global network of ground-based sun photometer stations (AERONET), and observations were made of atomic oxygen [OI] 557.7- and 630-nm emission lines at the Geophysical Observatory of the Institute of Solar-Terrestrial Physics, Siberian Branch, Russian Academy of Sciences (52° N, 103° E). A nonlinear characteristic of the correlation dependence was revealed between the intensities of the 557.7- and 630-nm emissions of the upper atmosphere and the aerosol optical depth (AOD): the correlation coefficients increased for small AOD (below 0.5) and decreased for large turbidities. We identified an observation period with a high positive correlation between the 557.7-/630.0-nm emission intensities and the AOD, presumably associated with vast forest fires.

First Joint Observations of Radio Aurora by the VHF and HF Radars of the ISTP SB RAS

Two modern radars for diagnosis of the ionosphere by the radio-wave backscattering method, namely, the Irkutsk incoherent scatter radar at VHF (IISR, 154–162 MHz) and the Ekaterinburg coherent radar at HF (EKB, 8–20 MHz) are operated at the Institute of Solar-Terrestrial Physics, Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS). The paper analyzes the results of joint observations of strong scattering (radio aurora) on June 8, 2015. To determine the geographical position of the radio aurora, we developed original methods that take into account both the features of the radio-wave propagation and the features of the radar antenna systems. It is shown that there are areas where the spatial position of the HF and VHF radio aurora can coincide. This permits using the radars as a single complex for diagnosis of the characteristics of small-scale high-latitude irregularities in the ionospheric E and F layers. A comparative analysis of the characteristics and temporal dynamics of the radio-aurora region in the HF and VHF ranges is performed. Using the DMSP satellite data, it has been shown that the radio aurora dynamics during this experiment with the EKB radar can be related with the spatial dynamics of the localized area with high electric field, which moves from high to equatorial latitudes. It is found that due to the broader field of view, radio aurora at the HF radar was stably observed 6–12 min earlier than at the VHF radar. This permits using the EKB radar data for prediction of the radio-aurora detection by the IISR radar.

Observations of the potentially hazardous asteroid 275677 and the modeling of its shape

Knowledge of the physical properties of asteroids is required in order to calculate the evolution of their orbits under the influence of nongravitational effects. Photometric observations of the potentially hazardous asteroid 275677 were conducted at the Sayan Solar Observatory of the Institute of Solar-Terrestrial Physics from March 25, 2014, through April 4, 2014 (at the time when this asteroid approached Earth). The period of rotation of the asteroid about its center of mass and the light curve, which defines the phase dependence of its brightness in a single rotation period, were determined based on the results of measurements performed by the Lafler-Kinman method. A model was constructed based on the obtained light curve. When this model was rotated, the variable component of the reflected radiation in a single revolution matched the variable component of the light curve of the asteroid. The range of possible directions of the axis of rotation of the asteroid was determined in the process of modeling.

The subsecond pulses during the August 10, 2011 flare by observations of RATAN-600 and the 4–8 GHz Siberian solar spectropolarimeter

We present the results of a study of the subsecond pulses (SSPs) registered in the microwaves during the C2.4 solar flare. The event occurred on August 10, 2011, in the 11236 active region near the western limb and reached a maximum at 0935 UT. Subsecond pulses were registered by RATAN-600 for the first time when this flare reached its maximum. The fact of detection of SSPs was confirmed by simultaneous observations carried out with a spectropolarimeter at the Radio Astrophysical Observatory, Institute of Solar-Terrestrial Physics. A former analysis of the emission nature of the main flare source revealed the presence of a high-temperature (T > 30 MK) source that determined both the microwave and X-ray emission parameters of this event. We have compared the temporal variations of the SSPs microwave emission with the variations of the plasma parameters (temperature and emission measure) taken from observations with the FERMI space telescope with a subsecond time resolution. The obtained results suggest that the nature of SSP generation, as well as of the flare itself, was determined by the high-temperature source.

Software system for automatic interpretation of ionosphere sounding data

The present paper is concerned with methods and algorithms of the software system for the automatic interpretation of radio physics information, as acquired by an FMCW ionosonde (at the Institute of Solar-Terrestrial Physics, Siberian Branch, Russian Academy of Sciences), which provides for vertical sounding (VS) and oblique sounding (OS) of the ionosphere. The following problems were considered within this problem: The method of interpreting ionograms is based on using simulation data for the frequency dependences of the long-term prediction propagation characteristics and the results of processing experimental data.

Small-amplitude oscillations in solar filaments

The temporal and spatial properties of small-amplitude oscillations have been studied using spectral observations of motions in solar filaments carried out at the Sayan Solar Observatory (Institute of Solar-Terrestrial Physics, Russian Academy of Sciences). Oscillations with different periods and spatial scales exist simultaneously in filaments. Swaying motions of filaments in the plane of the sky have been detected. The character of these oscillatory motions is compared with oscillations in the Doppler velocity at the same filament sites.

Mid-latitude airglow during heliogeophysical disturbances

This is a brief review of the results of studies on mid-latitude airglow of the Earth’s upper atmosphere carried out at the Institute of Solar-Terrestrial Physics in recent years.

Reaction of the ionospheric F1 region to disturbances in October and November 2003 (analysis from Irkutsk digisonde measurements)

We consider the ionospheric response at heights of 120–220 km to geomagnetic disturbances in October and November 2003, which caused a strongly pronounced decrease in the electron content in the noted height range. For this disturbance period, using a technique of the authors, midday variations of the relative content of atomic and molecular oxygen at a height of 120 km were estimated. This estimation was performed with the help of ionospheric measurements (by a digital ionosonde) conducted at the Institute of Solar-Terrestrial Physics of the Russian Academy of Sciences from 2003 to 2006. Comparison of these values with similar values from the mass spectrometer-incoherent scatter (MSIS)-86 model showed that our estimates during disturbance days were two times less. This study continues research into the field of using ionospheric measurements to estimate the relative gas composition of the thermosphere at heights below the maximum of the F2 layer.

Web-Based Data Processing System for Automated Detection of Oscillations with Applications to the Solar Atmosphere

A web-based, interactive system for the remote processing of imaging data sets (i.e., EUV, X-ray and microwave) and the automated interactive detection of wave and oscillatory phenomena in the solar atmosphere is presented.The system targets localised, but spatially resolved, phenomena, such as kink, sausage, and longitudinal propagating and standing waves. The system implements the methods of Periodmapping for pre-analysis, and Pixelised Wavelet Filtering for detailed analysis of the imaging data cubes. The system is implemented on the dedicated data processing server http://pwf.iszf.irk.ru, which is situated at the Institute of Solar-Terrestrial Physics, Irkutsk, Russia. The input data in the .sav, .fits or .txt formats can be submitted via the local and/or global network (the Internet). The output data can be in the png, jpeg and binary formats, on the user's request. The output data are periodmaps; narrowband amplitude, power, phase and correlation maps of the wave's sources at significant harmonics and in the chosen spectral intervals, and mpeg-movies of their evolution. The system was tested by the analysis throughout the EUV and microwave emission from the active region NOAA 10756 on 4 May 2005 observed with TRACE and the Nobeyama Radioheliograph. The similarity of the spatial localisation of three-minute propagating waves, near the footpoint of locally open magnetic field lines determined by the potential field extrapolation, in both the transition region and the corona was established. In the transition region the growth of the three-minute amplitude was found to be accompanied by the decrease in the line of sight angle to the wave propagation direction.

Application of the theoretical reference ionosphere model for calculating HF-radiowave propagation characteristics

We study the possibilities of the Theoretical Ionosphere Model (TIM) developed at the Institute of Solar-Terrestrial Physics, Siberian Branch, Russian Academy of Sciences, for calculating the HF-radiowave propagation characteristics. The results of simulation based on the TIM are compared with calculations based on the IRI model and data from experimental observations. Analysis of the results of calculations for the maximum usable frequency (MUF) have shown that with the same input data (coordinates of the receipt and transmission points, the route length, date, and time), the differences in the calculated MUFs (using two different models supplying radio routes with ionospheric information) amount to ∼1% in the daytime and reach 10% at night.

Calculations of the ionization drift velocity by the Titheridge method, based on the data obtained at the Irkutsk Digisonde

The applicability of the method proposed by Titheridge [1995] to the estimations of the ionization vertical drift velocity V is studied. The values of the F2-layer maximum height, hmF2, obtained from the measurements using the DPS-4 digital ionosonde at Irkutsk (Institute of Solar-Terrestrial Physics) in 2003–2006, are the initial data. The neutral gas parameters were calculated from the [Hedin, 1987] thermospheric model. The obtained calculations of the vertical ionization drift velocity are estimated by comparing with the [Hedin et al., 1991] empirical model. In some cases, good agreement with this model has been obtained. However, such agreement is registered not always, and the cause of such discrepancies is still unclear. The diurnal variations in the vertical ionization drift velocity in different seasons are also discussed.

Approximation of the electron concentration measurements in the middle ionosphere at low solar activity

The set of the electron concentration (N) measurements at heights of 120–200 km have been generalized using the regression equation from the semi-empirical model (SEM) previously developed by us. The digital ionosonde was used to obtain the data at the Institute of Solar-Terrestrial Physics in Irkutsk in 2003–2006. SEM describes the correlation between N and the thermospheric characteristics. As a result, the SEM version for low solar activity has been obtained. Studying the N approximation results in the above range of conditions indicated that the N values are described quite satisfactorily in different years and seasons and in the diurnal cycle. The deviations of the experimental N values from the calculated ones and the possible causes of these deviations are discussed. In many cases the deviations are probably related to the deviations of the real state of the thermosphere from the description taken from the MSIS-86 model. The achieved results indicate that the used model equation can be quite adequately used to generalize the experimental material and to describe the N behavior under different heliogeophysical conditions.

Interpretation of electron density measurements using a semiempirical model

An analysis of the electron density (N) measurements, performed using a semiempirical model describing the relation of N to the thermospheric characteristics and the integral flux of ionizing radiation energy (E), makes it possible to estimate the relative content of atomic oxygen, if we can assume that the E value is correctly described by the available model of the spectral distribution of the ionizing radiation energy. Alternatively, we can estimate E that should be used to coordinate the observed and computed values of N. Such estimations of the N measurements were performed at the Institute of Solar-Terrestrial Physics in 2003 and 2004. The discussed estimates were made for the average state of the thermosphere-ionosphere system during summer periods.

Electronic solar spectrum atlas of enriched functionality

Basic capabilities of the electronic solar spectrum atlas, together with the examples of its usage in observations or during the preparing to them, are presented. The program has been created at the Institute of Solar-Terrestrial Physics based on Liege Solar Spectrum Atlas and Kitt Peak Atlas and covers the spectral range from 3291 to 12000 A. The convenient interface allows us to easily move to the required spectral range in order to obtain information about a spectral line of interest by a single click as well as to search line parameters in the database and to make changes in it. The additional functional abilities have made the atlas useful when calibrating magnetographs and estimating instrumental polarization degree.