Irkutsk Incoherent Scatter Radar Research Articles

Diurnal variations of the ionospheric electron density height profiles over Irkutsk: Comparison of the incoherent scatter radar measurements, GSM TIP simulations and IRI predictions

The long-duration continuous Irkutsk incoherent scatter radar (ISR) measurements allowed us to obtain the monthly averaged height-diurnal variations of the electron density in the 180–600km altitudinal range for 4 four seasons (winter, spring, summer, autumn) and for two solar activity levels (low and moderate). Considering these electron density variations as “quiet ionosphere patterns” we compared them with the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) simulations and the International Reference Ionosphere (IRI) predictions. It was found that some observational features revealed from the ISR measurements are reproduced nicely by both the theoretical and empirical models, and some features agree better with the GSM TIP than with IRI. None of the models is able to reproduce a detailed multi-peak behavior of the electron density observed by ISR at ∼300km and above for the spring and autumn under low solar activity, while for the spring the GSM TIP tends to reproduce the morning and daytime peaks at the same local times as they are seen from the ISR observations.

Interferometric observation of Cygnus-А discrete radiosource scintillations at Irkutsk Incoherent Scatter radar

We propose a new method for analyzing data from the Irkutsk Incoherent Scatter Radar. The method allows us to accomplish interferometric observation of discrete cosmic radio source characteristics. In this study, we analyze ionospheric scintillations of the radio source Cygnus-A. Observations were made in 2013 during regular radar sessions within 5–15 days for different seasons; the effective time of observation was 15–30 minutes per day. For interferometric analysis, the properties of correlation (coherence) coefficient of two independent recording channels were used. The statistical analysis of data from the independent channels allows us to construct two-dimensional histograms of radio source brightness distribution with a period of 18 s and to determine parameters (the maximum position and the histogram width) representing position and angular size of the radio source for each histogram. It is shown that the change of statistical characteristics does not correlate with fluctuations in power (scintillations) of the signal induced by radio wave propagation through ionospheric irregularities.

Интерферометрические наблюдения мерцаний дискретного радиоисточника Лебедь-А на Иркутском радаре некогерентного рассеяния

We propose a new method for analysis of data from Irkutsk Incoherent Scatter Radar. The method allows us to accomplish interferometric observation of discrete cosmic radiosource characteristics. In this study, we analyzed ionospheric scintillations of the radio source Cygnus-A. Observations were made in 2013 during regular radar sessions within 5–15 days for different seasons, and the effective time of observation was 15–30 minutes per day. For interferometric analysis, the properties of correlation (coherence) coefficient of two independent recording channels were used. The statistical analysis of data from independent channels allows us to construct two-dimensional histograms of radiosource brightness distribution with period of 18 s and to determine parameters (the maximum position and the histogram width) representing position and angular size of radiosource for each histogram. It is shown that the change of statistical characteristics does not correlate with fluctuations in power (scintillations) of the signal caused by radiowave propagation through ionospheric irregularities.

Calculation of meridional neutral winds in the middle latitudes from the Irkutsk incoherent scatter radar

AbstractThis paper presents a consistent technique for velocity determination of meridional neutral winds from the Irkutsk incoherent scatter radar (IISR.) We calculated plasma drift velocity based on phase analysis of an autocorrelation function of an incoherent scatter signal. We also preliminary tested the described technique by determining several low‐orbit satellite velocities. Midlatitude meridional neutral winds were calculated using a “three‐beam” technique from the IISR velocity with taking into account motions due to electric fields across magnetic field lines in both meridional and zonal directions. It has been shown that an underestimated impact of the motions generated by electric fields can seriously interfere in determining wind velocities. The results obtained were compared with the modeled wind values.

Расчет нейтральных меридиональных ветров в средних широтах с помощью Иркутского радара НР

The paper sequentially presents technique for determining velocity of meridional neutral winds from the Irkutsk Incoherent Scatter Radar (IISR) data. Due to IISR specific features effective at other IS radars, techniques for determining ionosphere parameters, in particular plasma drift velocities, resulted in considerable variance of defined parameters. To measure the plasma drift velocity taking into account such IISR features, we have developed a special technique based on phase analysis of autocorrelation function of incoherent scatter signal. The technique needs to be tested, and for this purpose, an experiment was carried out to measure velocities of low-orbit satellites. However, methods for meridional neutral wind calculations used by many authors [Evans, 1970] with the use of drift velocities obtained before, resulted in great disagreements with empirical HWM93 and HWM07 wind models. In addition, simultaneous measurements at two frequencies at IISR showed that it was difficult to explain such differences without taking into account the cross-field movements. Possible underestimation of the impact of movements generated by electric fields can result in serious error in determining wind velocities. The paper considers improvements for methods of calculating winds, and shows that the results obtained with it are in a better agreement with wind models.

Особенности поведения ионосферы вблизи максимума ионизации по данным иркутского радара некогерентного рассеяния для низкой и умеренной солнечной активности

The study deals with morphological research into dynamics of electron density in the ionosphere at altitudes of 200–400 km based on continuous series of observations at Irkutsk Incoherent Scatter Radar in 2007–2014. Daily altitude variations of average electron density for all seasons (winter, spring, summer, and autumn) and for two levels of solar activity (low and moderate) are presented. We compared our results with those of similar investigations at incoherent scatter radars such as Millstone Hill, Arecibo, EISCAT, ESR, and AMISR. Daily variations of the electron content for two altitude ranges of 180–250 and 250–600 km from data of Irkutsk Incoherent Scatter Radar and ionosonde were analyzed.

A statistical study of internal gravity wave characteristics using the combined Irkutsk Incoherent Scatter Radar and Digisonde data

Using previously developed methods for determining the three-dimensional spatial–temporal structure of traveling ionospheric disturbances and the automatic detection of wave disturbances, we analyzed data obtained simultaneously with the Irkutsk Incoherent Scatter Radar and Irkutsk ionosonde. The analysis relies on long continuous series of observations acquired during winter seasons in 2010–2014. We obtained representative statistics of traveling ionospheric disturbances characteristics including the full velocity vector. We analyzed the characteristics of traveling ionospheric disturbances with 1–6h periods comparing them against the dispersion relations for internal gravity waves in the Boussinesq and Hines approximations. It was shown that, with due consideration for the horizontal neutral wind, most of the observed ionospheric disturbances agrees with the laws of internal gravity waves propagation in the upper atmosphere. It was found that azimuthal anisotropy of internal gravity waves characteristics allows us to obtain the diurnal variations of zonal and meridional neutral winds in the upper atmosphere.

Comprehensive study of disturbances of the neutral atmosphere and ionosphere parameters over Eastern Siberia during the 2013 January major sudden stratospheric warming

We investigated variations in the neutral atmosphere and ionosphere parameters within a large range of heights in the Eastern Siberia region during the 2013 January sudden stratospheric warming (SSW). The analysis is based on: the data from spectrometric measurements of OH (∼87km, 834.0nm, (6–2)) and At O2 (∼94km, 864.5nm, (0–1)) upper atmospheric emissions, the data from the Irkutsk DPS-4 Digisonde, the data on electron and ion temperatures and the meridional component of the neutral wind from the Irkutsk Incoherent Scatter Radar, the satellite data on the vertical temperature distribution in the atmosphere from Aura MLS v3.3, and the MERRA reanalysis data.We detected the disturbances of the neutral atmosphere temperature from the stratosphere to the mesosphere and lower thermosphere (MLT). The temperature at 10hPa (∼32km) increased by ∼70K up to ∼270K, the temperature at 0.01hPa (∼80km) decreased by 50K, and reached ∼170K. At the MLT heights, an increase in the intensities of the OH and O2 emissions by a factor of 2–2.5 relative to the undisturbed conditions was revealed. At the F2-layer height, the plasma parameter disturbances were found. After 2013 January 10, interruption of the correlation between NmF2 and hmF2 occurred. Ion temperature cooling reaching 50K was observed on January 1–10, changing to a quick increase by 50K for several days after January 10. The neutral wind meridional component and the electron temperature decreased over January 1–21.The observed effects can be probably caused by atmospheric circulation disturbances and amplification in the vertical transfer. The disturbances in the upper atmospheric and in ionospheric parameters during SSW can evidence the coupling between the lower and upper atmosphere.

Estimation of the plasmasphere electron density and O+/H+ transition height from Irkutsk incoherent scatter data and GPS total electron content

Observations obtained using the Irkutsk Incoherent Scatter Radar (ISR) and GPS Total Electron Content (TEC) were used for estimation of the O+/H+ transition level and electron density distribution in the upper topside ionosphere and in the plasmasphere. We use a modified Chapman function where O+/H+ transition level is one of parameters to develop a model. On the base of this model we consider some examples of O+/H+ transition height dynamics and estimate the uncertainty of the method. We show that the transition height dynamics is very sensitive to parameters of neutral wind and it has specific variation on Irkutsk ISR site. The plasmasphere can contribute more than 50% to GPS TEC, and the input from plasmasphere can produce significant influence on GPS TEC variations.

Studying of the spatial–temporal structure of wavelike ionospheric disturbances on the base of Irkutsk incoherent scatter radar and Digisonde data

In this paper the spatio-temporal structure of traveling ionospheric disturbances characteristics is studied on the base of the electron density profiles measured by two beams of the Irkutsk incoherent scatter radar and the Irkutsk Digisonde. The technique for determination of spatial–temporal structure of wavelike ionospheric disturbances was developed using cross-correlation and spectrum analysis of electron density. The automated method for extracting ionospheric disturbances including both long-period day-to-day variability and short-period variations has been developed. Full analyses of January 15–February 17, 2011 data, including total velocity vector, was carry out for 1–6h ionospheric disturbances, corresponding to internal gravitational waves. The propagation characteristics agree with those obtained from the known studies of the wavelike ionospheric disturbances. An automated method of ionospheric disturbances analysis was created on the basis of regular continuous measurements with the Irkutsk Digisonde. The statistical analysis of electron density disturbances was carried out for 2004–2009 period.

Perspectives of usage of Irkutsk incoherent scatter radar (IISR) as an imaging riometer and radio-heliograph

Space radio emission is the important source of background for radio physical investigation of the ionosphere. Variations of the background signal and scintillations of the discrete radio sources allow defining some ionosphere characteristics such as plasma density variations and degree of plasma inhomogeneity. Irkutsk incoherent scatter radar (IISR) has narrow palm-like directivity diagram. With this diagram IISR scans a wide sector of elevation angles of the celestial sphere. The sweeping time of a 40° sector with 0.5° step is around several seconds. Therefore, IISR in the passive mode is capable to work as an imaging riometer. As a result of several month passive mode observations we detected a number of scintillation events and found a good agreement between the scintillation and spread-F events which were observed independently. IISR in the passive mode is also sensitive to the solar events and probably capable to observe solar radio emission objects with good time resolution and in a wide spatial range.

Effective subtraction technique at the Irkutsk Incoherent Scatter Radar: Theory and experiment

We describe a sounding technique that allows us to improve spatial resolution at the Irkutsk Incoherent Scatter Radar (IISR) without losing spectral resolution. The technique also allows us to decrease temperature estimation errors caused by the Faraday effect. The technique is based on transmitting various duration pulses without any modulation and on subtracting correlation matrices of the received signal grouped by sounding pulse duration. We show theoretically and experimentally that the technique allows us to solve the problem of improving spatial resolution. Accumulation time for the technique is approximately four times longer than that for the alternating codes technique with the same spatial resolution.The number of lags in the correlation function with high spatial resolution does not depend on necessary spatial resolution. In the proposed technique, all the lags are obtained with the same spatial resolution and with the same signal-to-noise ratio. The technique is valid within the quasi-static ionospheric parameter approximation.

The technique of coherent echo processing in the approximation of a small number of point scatterers

In this paper, we aim at studying the structure of individual samples of coherent echo signals and determining signal features that permit one to detect coherent backscatter and also improve the methods of signal processing. We offer a model of the received signal in the form of a square pulse with duration of the order of the sounding pulse length and filled with a sinusoidal signal of arbitrary frequency. It is shown that this model is quite effective to interpret coherent echo signals in some cases. There are two ways of practical use of the model. One is a technique which singles out the sounding sessions in which strong coherent echo signals are distinguished against the background of other signals received by the Irkutsk incoherent scatter radar. Another is a technique of the spatial resolution improvement.

Discrete direction method in nonlinear problem of incoherent scattering spectrum fitting

A new fitting technique based on functional partition by simplexes of the nth order is developed to determine ionospheric plasma parameters with spectral measurement data from the Irkutsk incoherent scatter radar. In this approach, the search for a minimum of a multidimensional functional is reduced to a minimized calculation of model functions in each iteration. The algorithm also allows simplification of the search-stop criterion.

An analysis of the topside ionosphere parameters based on the long-duration Irkutsk incoherent scatter radar measurements

The topside ionosphere parameters are studied based on the long-duration Irkutsk incoherent scatter radar (52.9N, 103.3E) measurements conducted in September 2005, June and December 2007. As a topside ionosphere parameter we chose the vertical scale height (VSH) related to the gradient of the electron density logarithm above the peak height. For morphological studies we used median electron density profiles. Besides the median behavior we also studied VSH disturbances (deviations from median values) during the magnetic storm of September 11th 2005. We compared the Irkutsk incoherent scatter radar data with the Millstone Hill and Arecibo incoherent scatter radar observations, the IRI-2007 prediction (using the two topside options) and VSH derived from the Irkutsk DPS-4 Digisonde bottomside measurements.

Studying the fine structure of coherent echo spectra using data from Irkutsk incoherent scatter radar

Studying the processes generating different-scale inhomogeneities is one of the challenging problems of ionospheric physics. Plasma instabilities are one of the physical mechanisms by which small-scale inhomogeneities are formed. The main forms of instability in the ionospheric E-layer are two-stream and gradient-drift ones. The inhomogeneities generated by them lead to an abnormally intense radio scattering of different wavelengths (known as coherent echo (CE) or radio aurora) in the E-layer. Therefore, the method of radiowave backscattering is among the widely used methods for studying such inhomogeneities. The CE phenomenon has been investigated most intensely at high and equatorial latitudes, where the conditions for the CE origination are formed rather regularly. For the last decade, CE has also been intensely studied at midlatitudes, where it is observed less frequently and its formation conditions are less known. In 1998–2006, the purposeful studies of the midlatitude CE peculiarities were performed at the Irkutsk incoherent scatter (IS) radar, with a particular emphasis on its coherent properties. It was for the first time found out that the spectra of some data sets had a fine comb-shaped structure, which generated well-known single-humped CE spectra as a result of statistical averaging. In the scope of this study, unique coherent methods for processing individual data sets of CE signals were developed, making it possible to reveal the peculiarities of unaveraged CE-signal spectra. To describe these peculiarities, we proposed a new model of the inhomogeneity spectrum, which is the superposition of the discrete set of spatial harmonics with close wave numbers. The model was shown to adequately describe the scattered signal characteristics observed experimentally.

Correlation method for determining the ionospheric plasma drift velocity at the Irkutsk Incoherent Scatter Radar

The correlation method for processing the Irkutsk Incoherent Scatter Radar (IISR) data and the method for calculating the ionospheric plasma drift velocity are described. The properties of the complex autocorrelation function of an incoherent scatter signal are considered. The IISR data for September 2005 are analyzed.

Response of the midlatitude ionosphere to extreme geomagnetic storms of the 23rd solar cycle

The ionospheric response in the Irkutsk region (52.3° N, 104.3° E) to the extreme geomagnetic storms of solar cycle 23 was studied based on the data of the Irkutsk incoherent scatter radar (ISR) and DPS-4 vertical sounding digital ionosonde. The deviations of parameters from the undisturbed level, i.e., from the monthly medians or the values obtained on a quiet day, were considered as an ionospheric response. Values of the electron concentration maximum (NmF2) and electron temperature (Te) at a height of 350 km were chosen as parameters. The ionospheric response is interpreted in the scope of the concept of a thermospheric storm and penetration of the magnetospheric electric field.

Determining the parameters of the layer of scattering irregularities, forming coherent echo, according to the Irkutsk IS Radar data

The method for determining the parameters of the layer of scattering irregularities, form coherent echo, based on the Irkutsk Incoherent Scatter (IS) Radar data is presented. It has been indicted that the method has the necessary accuracy. The processing of experimental data for the periods of September 25–26, 1998, and July 15–16, 2000, indicated that our results are in good agreement with the data obtained by other researchers. The analysis of the experiments with a high time resolution made it possible to reveal the time variation in the determined parameters. The time variations in the layer thickness and height do not contradict the data obtained by other researchers, and the time variations in the angular sensitivity of irregularities has been observed for the first time and requires further studies.

Recording and control digital systems of the Irkutsk Incoherent Scatter Radar

A brief technical description of the Irkutsk Incoherent Scatter Radar of the Institute of Solar-Terrestrial Physics (Siberian Branch, Russian Academy of Sciences) is given. New diagnostic capabilities resulting from the radar upgrade are presented. Types of measurements for the Earth’s upper atmosphere and near-Earth space studies are described.