Heliogeophysical Conditions Research Articles

Features of backscatter ionospheric sounding as studied with a chirp ionosonde

We present the results of the studies of backscatter ionospheric sounding (BS) on the basis of a multipurpose chirp ionosonde developed in ISTP SB RAS. We analyze BS experimental data obtained during different seasons from 2005 to 2009. The accumulated dataset allows us to investigate features of BS signal propagation in various heliogeophysical conditions. To analyze and interpret BS signals on ionograms, we use the results of modeling of characteristics for chirp signals in the backscatter and oblique ionospheric sounding under a waveguide approach. We have revealed the most characteristic types of ionograms and have established conditions of appearance of a given type depending on the time of day, season, sounding direction, and medium conditions. In winter, spring, and autumn, the prevailing types of ionograms are those with BS signals corresponding to the propagation mode through reflection from the F layer. Signals reflected by E or Es layers are recorded during summer periods. At the same time, frequencies of the received signals are sufficiently large, and sometimes there are no reflections from the F layer.

Исследование особенностей возвратно-наклонного зондирования ионосферы на базе ЛЧМ-ионозонда

We present the results of studies of backscatter ionospheric sounding (BS) on the basis of a multipurpose chirp ionosonde developed in ISTP SB RAS. We analyze BS experimental data obtained during different seasons from 2005 to 2009. The accumulated dataset allows us to investigate features of BS signal propagation in various heliogeophysical conditions. To analyze and interpret BS signals on ionograms, we use the results of modeling of characteristics for chirp signals in the backscatter and oblique ionospheric sounding under the waveguide approach. We have revealed the most characteristic types of ionograms and have established conditions of appearance of a given type depending on the time of day, season, sounding direction, and medium conditions. In winter, spring, and autumn, the prevailing types of ionograms are those with BS signals corresponding to the propagation mode through reflection from the F layer. Signals reflected by E or Es layers are recorded during summer periods. At the same time, frequencies of the received signals are sufficiently large, and sometimes there are no reflections from the F layer.

Statistical simulation of variations in medical characteristic during heliogeophysical disturbances

Heliobiological studies, although recently very active, have failed to provide a full understanding of the Sun–biosphere interaction mechanisms. This is because the forecasts of bio tropic effects of the active Sun, like geophysical forecasts, are mostly determined by empirical patterns and are of a probability character. To obtain probability predictions, an adequate statistical model should be prepared. This is what is treated in this work. The time series of data from medical studies have undergone the trend treatment. The samples were sorted by the state of heliogeophysical conditions, and statistical distributions and invariants have been calculated down to the forth order. The analysis has shown that during heliogeomagnetic disturbances the obtained distributions differ from the Gaussian law. Therefore, an attempt at a statistical description of medical characteristics was made on the basis of the Poisson model. For our samples, the characteristic function of the exponential kind was chosen under the assumption that time series are the superposition of some, determined or random, process. Through the Fourier transform, the characteristic function was transformed into a nonholomorphic expressiveasymmetrical function of the probability density. The statistical distributions, calculated for the studied samples over perturbation periods, were compared with the obtained model function of distribution. The probability of coincidence for a posteriori distributions by the criterion χ2 is Р ~ 0.7–0.9. Our analysis has allowed a conclusion about the applicability of a model based on the Poisson random process for statistical description and appraisals of the probability of changes in the number of vascular bouts and strokes during heliogeophysical perturbations.

Response of the auroral lower ionosphere to solar flares in March 2012 according to ELF observations

The response of the lower ionosphere to the solar flares that occurred in March 2012 is considered. Measurements of the propagation velocity and wave impedance of ELF electromagnetic pulses (atmospherics) performed at Lovozero and Barentsburg high-latitude observatories were used to estimate this response. It was shown that the daily average propagation velocity of atmospherics decreased by 20–30 thousand km/s under disturbed heliogeophysical conditions as compared to the velocity measured under quiet conditions. This is related to a decrease in the effective waveguide height that results from the change in the ionospheric conductivity profile during a solar flare. It was detected that pronounced bursts of wave impedance, the maximums of which exceed the impedance average value by a factor of more than 2, are observed during strong heliogeophysical disturbances. This fact cannot be explained in the scope of a spherically layered model; consequently, such deviations indicate an increase in the D-layer conductivity inhomogeneities.

Прогноз характеристик распространения декаметровых радиоволн на основе глобальной модели ионосферы и плазмосферы

We present the forecast results of maximal usable frequencies for mid-latitude paths on the base of complex We present the results of forecasting maximum usable frequencies (MUF) on middle-latitude paths on the basis of complex algorithm including modules of the ionosphere and plasmasphere global model (IPGM) and the model of radio wave propagation. The computation of propagation characteristics for decameter radio waves is carried out within the framework of normal wave technique. IPGM developed in ISTP SB RAS enables to compute electron concentration profiles and effective frequency of collisions using minimum number of input data and taking into account physical processes in the Earth’s upper atmosphere. To estimate the efficiency of using IPGM in long-term forecast of radio wave propagation we computed MUF for radio communication in various heliogeophysical conditions. To obtain precision characteristics of MUF forecast we used experimental data of oblique sounding on Magadan–Irkutsk, Khabarovsk–Irkutsk, Norilsk–Irkutsk paths. The paths are equipped with modern ionosphere diagnostic hardware for oblique sounding by continuous chirp signal. We also compared results of MUF forecast using IPGM with computations carried out according IRI model.

Empirical model of variations in the upper atmosphere continuum emission. 3. Emitting-layer altitude

The specific features and variations in the continuum emission volume intensity for different heliogeophysical conditions were revealed based on rocket and satellite measurements of this emission in the upper atmosphere in the visible spectral region. It was indicated that the main interval of the continuum emitting layer related to the NO + O process is located at an altitude of 80–110 km. If an emission is caused by the interaction between nitrogen oxide and ozone molecules in disturbed and undisturbed states, the emission emitting layer covers the entire middle atmosphere above the troposphere.

Remote sensing of ELF/VLF radiation induced in experiments on artificial modification of the ionosphere

In 2012, remote measurements of electromagnetic signals in the ELF/VLF band were taken at different points in Russia during experiments on artificial ionospheric modification with the powerful HF wave at the EISCAT heating facility (Tromso, Norway). The use of the new, highly sensitive magnetometric equipment allowed signals with an amplitude of a few femtoteslas to be recorded at a distance of up to 2000 km from the source. Analysis of the measurement results discovered substantial differences in the amplitude-phase characteristics of the signals, which were caused by a change in helio-geophysical conditions in the region of heating and along the signal passage route, and features of signal propagation, which are related to their mode of guided propagation, the directivity of the source, and angles of reception.

Empirical model of variations in the continuum emission in the upper atmosphere. 1. Intensity

The ground-based and satellite measurements of the upper-atmosphere continuum (continuous emission) intensity in the visible and near IR spectral regions have been analyzed. The data were obtained at the geophysical stations, located in different regions of the globe, and at Mir Space Station. The regularities in the spectral distribution of the continuum emission intensity and emission variations have been revealed for different heliogeophysical conditions.

On the possibility of localization of a substorm by using the “Sura” heating facility

We present the results of analysis of helio-geophysical conditions for the experiments performed in 2007-2010 to study modification of the ionosphere by high-power radio emission of the “Sura” heating facility. The feature of the experiments is that the operating frequency of the facility exceeded the upper-hybrid frequency for the F2 layer maximum in the ionosphere. All the experiments were performed in the local-time sector of the Harang discontinuity (i.e., from 21:00 to 00:00, local time) to ensure the most probable influence of the facility operation on the onset of natural processes in the subauroral region of the ionosphere. At least two experiments were found to demonstrate that the observed substorm activity in the region of the modification produced by the facility could be stimulated by its operation. The results of the ground- and satellite-based measurements, both in the vicinity of the “Sura” facility and in the magnetically conjugate region, confirm the conclusion about the possibility of substorm localization by this facility.

Deterioration in the accuracy of GPS system positioning due to the effect of ionospheric bubbles

The state of the ionosphere affects the operational stability of satellite radio navigation systems. The dense network of GEONET GPS sites on the territory of Japan allows to conduct a thorough investigation of the stability of system operation at mid-latitudes in different heliogeophysical conditions. This paper considers deterioration in the accuracy of GPS system positioning due to the effect of a large-scale ionospheric disturbance (an ionospheric bubble) over Japan on February 12, 2000.

10.1007/s11478-008-2016-1

The empirical approximations of variations in the rotational temperature of the emission of the molecular oxygen Atmospheric system, obtained based on the systematization of the long-term ground-based observations under different heliogeophysical conditions, are presented.

10.1007/s11478-008-1010-y

Using model simulations, the morphological picture (revealed earlier) of the disturbances in the F 2 region of the equatorial ionosphere under quiet geomagnetic conditions (Q-disturbances) is interpreted. It is shown that the observed variations in the velocity of the vertical E × B plasma drift, related to the zonal E y component of the electric field, are responsible for the formation of Q-disturbances. The plasma recombination at altitudes of the lower part of the F 2 region and the dependence of the rate of this process on heliogeophysical conditions compose the mechanism of Q-disturbance formation at night. The daytime positive Q-disturbances are caused exclusively by a decrease in the upward E × B drift, and this type of disturbances could be related to the known phenomenon of counter electrojet. Possible causes of formation of the daytime negative Q-disturbances are 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.

Provision of the required navigation characteristics of satellite radio navigation systems in unfavorable helio-geophysical conditions

A detailed review of domestic and foreign scientific publications, dedicated to the influence of geomagnetic disturbances and powerful bursts of the Sun’s radio radiation on the operation quality of satellite radio navigation systems (SRNS) and their functional additions, is performed. It is shown that existing methods of providing the required radio navigation characteristics during operation of the SRNS user’s device in the autonomous and differential modes do not fully satisfy modern requirements to SRNS in the conditions of influence of unfavorable helio-geophysical factors. A system of organization-technical measures targeted at provision of the required precision and continuity of the position determination of SRNS users under influence of geomagnetic disturbances and bursts of solar radio radiation is considered. For the practical realization of these measures an approximate structure of the complex system to provide the required characteristics of SRNS in unfavorable helio-geophysical conditions is suggested. This system may be considered as a necessary component of the perspective service of global monitoring and forecasting of the SRNS operation quality.

Electron density profile calculation technique for Autoscala ionogram analysis

An electron density profile model with free parameters is introduced. Initially the parameters are calculated on the basis of the ionospheric characteristics automatically obtained from the ionograms by Autoscala and considering the helio-geophysical conditions. The technique used to adjust the free parameters to the particular ionograms recorded is presented.

Empirical model of variations in the emission of the molecular oxygen Atmospheric system. 2. Temperature

The empirical approximations of variations in the rotational temperature of the emission of the molecular oxygen Atmospheric system, obtained based on the systematization of the long-term ground-based observations under different heliogeophysical conditions, are presented.

Preliminary results of TEC measurements in Guwahati, India

A dual frequency GPS receiver was installed in Guwahati, India (latitude 26.2°N, longitude 91.75°E, dip +35°) in January 2006 in the framework of an Indian–Russian project of seismo-ionospheric effects searching and investigation. It is quite clear that manifestations of such effects should be strongly dependent (among others) on regional features of ionosphere. In our case formation of the equatorial anomaly will affect the results. So, the data of half a year of observations were analyzed to establish the behavior of Total Electron Content (TEC) in a region of Northern crest of the equatorial anomaly in quiet helio-geophysical conditions as a background for detecting the impact of effects from below.

Mechanism of formation of Q-disturbances in the F 2 region of the equatorial ionosphere

Using model simulations, the morphological picture (revealed earlier) of the disturbances in the F2 region of the equatorial ionosphere under quiet geomagnetic conditions (Q-disturbances) is interpreted. It is shown that the observed variations in the velocity of the vertical E × B plasma drift, related to the zonal Ey component of the electric field, are responsible for the formation of Q-disturbances. The plasma recombination at altitudes of the lower part of the F2 region and the dependence of the rate of this process on heliogeophysical conditions compose the mechanism of Q-disturbance formation at night. The daytime positive Q-disturbances are caused exclusively by a decrease in the upward E × B drift, and this type of disturbances could be related to the known phenomenon of counter electrojet. Possible causes of formation of the daytime negative Q-disturbances are discussed.

Empirical model of variations in the OI 630 nm emission. 1. Intensity

The empirical model of variations in the atomic oxygen emission intensity depending on different heliogeophysical conditions such as nighttime, lunar time, lunar phase age, season, year, and solar activity level during the 11-year cycle, as well as on cyclic aperiodic activity variations, level of geomagnetic disturbances, and their manifestations in the form of midlatitude subauroral red arcs, has been developed based on the long-term measurements of this emission intensity.

The kriging method of TEC instantaneous mapping

The spatial variations of total electron content (TEC) over the European area for single epochs are examined using a so-called instantaneous mapping procedure applied to simultaneous data collected from a limited number of measuring stations. The method of map generation is explained involving an application of the kriging technique and construction of the associated semi-variogram. Examples of maps thereby produced are presented for magnetically quiet and disturbed days and their spatial structures are discussed in terms of the prevailing helio-geophysical conditions.