Radio Solar Telescope Network Research Articles

Study on the Temporal Evolution of the Radial Differential Rotation of Solar Corona Using Radio Emissions

The daily measurements of the disk-integrated solar radio flux, observed by the Radio Solar Telescope Network, at 245, 410, 610, 1415, 2695, 4995, and 8800 MHz during the time interval of 1989 January 1 to 2019 December 17, are used to investigate the temporal evolution of radial differential rotation of the solar corona using the methods of ensemble empirical mode decomposition (EEMD) and wavelet analysis. Overall, the results reveal that over the 30 yr period, the rotation rates for the observed solar radio flux within the frequency range of 245–8800 MHz show an increase with frequency. This verifies the existence of the radial differential rotation of the solar corona over long timescales of nearly three solar cycles. Based on the radio emission mechanism, to some extent, the results can also serve as an indicator of how the rotation of the solar upper atmosphere varies with altitude within a specific range. From the temporal variation of rotation cycle lengths of radio flux, the coronal rotation at different altitudes from the low corona to approximately 1.3 R ⊙ exhibits complex temporal variations with the progression of the solar cycle. However, in this altitude range, over the past 30 yr from 1989 to 2019, the coronal rotation consistently becomes gradually slower as the altitude increases. Finally, the EEMD method can extract rotation cycle signals from these highly randomized radio emissions, and so it can be used to investigate the rotation periods for the radio emissions at higher or lower frequencies.

Solar radio bursts impact on the International GNSS Service Network during Solar Cycle 24

Solar radio bursts (SRB) are a known source of noise for Global Navigation Satellite Systems (GNSS) such as GPS or Galileo. They can degrade the carrier-to-noise ratio of satellite signals, thereby diminishing system performance and, in severe cases, causing total service outages. Although a small amount of particularly intense events have already been studied in detail, the commonness and intensity of SRBs that could potentially impair GNSS performance remain uncertain. This study broadens the scope beyond merely extreme SRBs, studying the impact of SRBs on GNSS throughout Solar Cycle 24. Solar 1.4 GHz observations from the Radio Solar Telescope Network are used to find the 20 most intense SRBs at that frequency. The impact of each SRB is then evaluated in terms of GNSS signal strength decrease, reduction in the number of available satellites, and precision degradation. The results show that at the GPS L1 frequency only one event presented extended service degradation, while at the L2 frequency, minimum operational requirements were not met by at least one station during seven of the SRBs. Only a modest correlation between performance degradation and SRB intensity is found. In particular, it is reported how some mild SRBs affected satellite signals while others almost ten times more intense went unnoticed. The fundamental role that the SRB circular polarization plays in these discrepancies is shown with new 1.4 GHz circular polarization observations from the SMOS satellite. The different responses of GNSS receivers to SRBs depending on the receiver manufacturer are also explored.

Analysis of the Radio Solar Telescope Network's Noon Flux Observations Over Three Solar Cycles (1988–2020)

AbstractThe Sun is a readily accessible source of wideband noise that can be used for the calibration of a wide variety of radio systems. Since 1979 the United States Air Force Radio Solar Telescope Network (RSTN) has performed solar flux observations around noon on eight frequencies between 245 and 15,400 MHz. These fluxes are disseminated by the National Ocean and Atmospheric Administration (NOAA) and are used by many radio and radar system operators to perform system calibration. Little analysis has been performed on the RSTN noon flux values. Here we review the calibration procedures of RSTN and perform statistical tests between the four sites comprising RSTN. For system operators who require precise system calibration the noted variations may be large enough to cast doubt on RSTN flux values for such calibration. However, for many communication systems a calibration within one or two dB is adequate. We discuss the reported variation both in linear and logarithmic terms. When it is possible to used smoothed data the inter‐site variation becomes less of a problem, although the correlation between sites at Ku band (15,400 MHz) still appears excessively large. We update some simple empirical models for wideband solar flux based purely on the 10 cm flux at any time, as these have also been used in solar radio calibration procedures. We give practical advice on the use of solar flux for radio system calibration and make some recommendations that we believe could improve the accuracy and utility of solar radio flux reports.

Quiet-Filament Eruptions and Coronal Jets as Causes of Depressions in Microwave Radio Emission

Several solar events with different types of negative microwave bursts have been studied using data from different spectral ranges. The total radio flux data obtained at the Ussuriysk Observatory, the Nobeyama Observatory, the US Air Force Radio Solar Telescope Network (RSTN), and the spectropolarimeter of the Institute of Solar–Terrestrial Physics, Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS) were used. The images were analyzed using data from the SDO/AIA space observatory in the 304 Å channel and the Nobeyama radio heliograph at a frequency of 17 GHz. It was shown that the “isolated” depressions of radio emission were caused by the absorption of radiation from radio sources and/or vast regions of the quiet Sun by low-temperature material of a large eruptive filament in the absence of flares. This confirmed the conclusions of the previous studies. It was revealed that the cause of negative bursts of the “pre-burst depression” type was the screening of a near-limb radio source by the material of coronal jets. In the case of a weak flare accompanying the jet, the negative burst could also be of the “isolated” type. A case of a previously unreported occurrence of a deeper depression of radio emission at high frequencies as compared to low frequencies was considered. It was shown that negative bursts are not as rare phenomena as previously thought.

RMCSat: An F10.7 Solar Flux Index CubeSat Mission

The F10.7 solar flux index is a measure of microwave solar emissions at a wavelength of 10.7 cm or 2800 MHz. It is widely used in thermosphere and ionosphere models as an indicator of solar activity and is recorded at only one terrestrial observatory in Penticton, Canada during daylight hours. The lack of geographical and temporal coverage of F10.7 measurements and no external redundancy to the existing system has led to the development of the RMCSat mission, which seeks to demonstrate the feasibility of collecting microwave solar flux emissions from a space-based platform. RMCSat is the first CubeSat mission by the Royal Military College of Canada. It offers a training environment for personnel in space mission analysis and design, satellite assembly, integration and testing, and satellite operations. This paper introduces the mission concept and preliminary design of a space-based solution that captures solar density flux measurements during each orbit as the Sun passes through the boresight of the primary payload antenna. In addition to two channels recording the 2800 MHz frequency (2785 MHz and 2815 MHz), a third channel records 2695 MHz using the same calibration standard to determine if the United States Radio Solar Telescope Network (RSTN) could be leveraged to supplement the existing F10.7 solar flux measurements and improve solar flux approximations. The RMCSat mission, satellite design, and system budgets are demonstrated here as being viable. Future design considerations pertain to the payload antennas and achievable launch orbits.

Broken Power-law Energy Spectra of the Accelerated Electrons Detected in Radio and Hard X-Rays during the SOL2013-05-13 Event

Abstract Solar flares, resulting from magnetic activity of the Sun, are among the most energetic events in the solar system and in extreme cases directly affect our highly technological society. In this work, we analyze a solar flare detected at millimeter and centimeter wavelengths, as well as X-rays above 1 MeV. Observations of solar flares at these energy bands provide diagnostics of the energetic accelerated electrons and the magnetic fields where the emission is produced. During the SOL2013-05-13 solar flare, radio data were obtained by the telescope system POlarisation Emission of Millimeter Activity at the Sun, which observes the Sun at 45 and 90 GHz with polarization measurements, and at microwaves (1–15 GHz) by the Radio Solar Telescope Network. For the same event, X-ray emission was detected by the RHESSI and Fermi satellites. Spectra at both wavelengths were constructed and fit separately to yield the accelerated electron energy distribution that produced the emission. The optically thin radio spectral index was calculated by fitting the Ramaty model of gyrosynchrotron emission to the observed radio spectrum, whereas the hard X-ray spectral index was obtained from the spectral fit assuming a thermal emission model plus a nonthermal broken power-law distribution. Finally, both spectral indexes were compared and confirmed that the index obtained from the radio spectrum agrees with the index of the X-ray spectrum for energies above the break energy of ∼600 keV. Thus, the hard X-rays more energetic than 600 keV and high radio frequencies of solar flares are emitted by the same population of high-energy accelerated electrons. This result indicates that the accelerated electrons have an energy distribution best represented by a broken power law, with a breakup above energies around 1 MeV.

RELATIONSHIP OF SCR, CME AND CORONAL SHOCK WAVES WITH THE PARAMETERS OF TYPE IV AND II SOLAR RADIO BURSTS

ABSTRACT. This paper presents the results of a comparative analysis of the relationship between solar cosmic rays (SCR), coronal mass ejections (CME), and coronal shock waves (CSW) with the parameters of solar continual type IV radio bursts, as well as with the parame- ters of type II radio bursts. The sample under study con- tains 147 proton events accompanied by type IV continu- um radio bursts in the 25-15400 MHz range, type II radio bursts in the 25-180 MHz range, as well as CME and cor- onal shock waves. For the analysis, we used original rec- ords of solar radio emission at 8 fixed frequencies in the range 245-15400 MHz according to data from RSTN (Ra- dio Solar Telescope Network), original records of dynam- ic spectra from SRS (Solar Radio Spectrograph) in the range of 25-180 MHz, as well as original records intensity of the flux of SCR protons with proton energies in the range> 1-100 MeV according to data from the GOES spacecraft. A comparative analysis showed that the rela- tionship between the intensity of the SCR proton flux and the CME velocity is, on average, much stronger with the parameters of type IV radio bursts than with the parame- ters of type II radio bursts, which indicates the dominant role of the SCR acceleration process in the flare region, rather than shock waves. However, detailed studies of the fine structure of type II radio bursts have shown that there is a fairly strong relationship between the intensity of the flux of mean-relativistic protons I p and the frequency f min,1 at the fundamental harmonic (at the 1-st harmonic) at the time t min corresponding to the minimum relative distance b min between the harmonics of type II radio bursts. De- tailed studies of the fine structure of type II radio bursts have also shown that there is a strong relationship between the intensity of the SCR proton flux I p and parameter V II , which characterizes the displacement of the shock front with time t i in a narrow frequency range of 25-60 MHz.

Inferring the Magnetic Field Asymmetry of Solar Flares from the Degree of Polarisation at Millimetre Wavelengths

Polarisation measurements of solar flares at millimetre-waves were used to investigate the magnetic field configuration of the emitting sources. We analyse two solar flares (SOL2013-02-17 and SOL2013-11-05) observed by the POlarisation Emission of Millimetre Activity at the Sun (POEMAS) at 45 and 90 GHz, at microwaves from 1 – 15 GHz by the Radio Solar Telescope Network (RSTN), and at high frequencies (212 GHz) by the Solar Submillimetre Telescope (SST). Also, hard X-rays from these flares were simultaneously detected by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). The flux and polarisation radio spectra were fit using a model that simulates gyrosynchrotron emission in a spatially-varying 3D magnetic field loop structure. For the modelling, the magnetic loop geometry was fixed and the field strength was the only free parameter of the magnetic field. In addition, a uniform electron distribution was assumed by the model, with the number density of energetic electrons and the electron spectral index as free parameters. The fitted model reproduced reasonably well the observed degree of polarisation and radio flux spectra for each event yielding the physical parameters of the loop and flaring sources. Our results indicate that the high degree of polarisation during a solar flare can be explained by two sources located at the footpoints of highly asymmetric magnetic loops whereas low polarisation degrees arise from footpoint sources of symmetric magnetic loops.

On the Evolution of Bands in the Dynamic Spectra of Solar Type II Radio Bursts

Based on an analysis of the dynamic spectra for solar flares in the meter wavelength range obtained with the ground-based Radio Solar Telescope Network, we consider the evolution of the parameters of harmonics in solar type II radio bursts. We have established that the relative separation between the bands behaves nonmonotonically and its value can change in a wide range, from 0.1 to 3. This can be explained by the generation of electromagnetic waves at the first and second harmonics of the plasma frequency on different sides of the shock front. We discuss the consequences of our results.

Millimeter and X-Ray Emission from the 5 July 2012 Solar Flare

The 5 July 2012 solar flare SOL2012-07-05T11:44 (11:39 – 11:49 UT) with an increasing millimeter spectrum between 93 and 140 GHz is considered. We use space and ground-based observations in X-ray, extreme ultraviolet, microwave, and millimeter wave ranges obtained with the Reuven Ramaty High-Energy Solar Spectroscopic Imager, Solar Dynamics Observatory (SDO), Geostationary Operational Environmental Satellite, Radio Solar Telescope Network, and Bauman Moscow State Technical University millimeter radio telescope RT-7.5. The main parameters of thermal and accelerated electrons were determined through X-ray spectral fitting assuming the homogeneous thermal source and thick-target model. From the data of the Atmospheric Imaging Assembly/SDO and differential-emission-measure calculations it is shown that the thermal coronal plasma gives a negligible contribution to the millimeter flare emission. Model calculations suggest that the observed increase of millimeter spectral flux with frequency is determined by gyrosynchrotron emission of high-energy ( $\gtrsim 300$ keV) electrons in the chromosphere. The consequences of the results are discussed in the light of the flare-energy-release mechanisms.

Probing Twisted Magnetic Field Using Microwave Observations in an M Class Solar Flare on 11 February, 2014

This work demonstrates the possibility of magnetic field topology investigations using microwave polarimetric observations. We study a solar flare of GOES M1.7 class that occurred on 11 February, 2014. This flare revealed a clear signature of spatial inversion of the radio emission polarization sign. We show that the observed polarization pattern can be explained by nonthermal gyrosynchrotron emission from the twisted magnetic structure. Using observations of the Reuven Ramaty High Energy Solar Spectroscopic Imager, Nobeyama Radio Observatory, Radio Solar Telescope Network, and Solar Dynamics Observatory, we have determined the parameters of nonthermal electrons and thermal plasma and identified the magnetic structure where the flare energy release occurred. To reconstruct the coronal magnetic field, we use nonlinear force-free field (NLFFF) and potential magnetic field approaches. Radio emission of nonthermal electrons is simulated by the GX Simulator code using the extrapolated magnetic field and the parameters of nonthermal electrons and thermal plasma inferred from the observations; the model radio maps and spectra are compared with observations. We have found that the potential magnetic field approach fails to explain the observed circular polarization pattern; on the other hand, the Stokes $V$ map is successfully explained by assuming nonthermal electrons to be distributed along the twisted magnetic structure determined by the NLFFF extrapolation approach. Thus, we show that the radio polarization maps can be used for diagnosing the topology of the flare magnetic structures where nonthermal electrons are injected.

Estimation of a coronal mass ejection magnetic field strength using radio observations of gyrosynchrotron radiation

Coronal mass ejections (CMEs) are large eruptions of plasma and magnetic field from the low solar corona into interplanetary space. These eruptions are often associated with the acceleration of energetic electrons which produce various sources of high intensity plasma emission. In relatively rare cases, the energetic electrons may also produce gyrosynchrotron emission from within the CME itself, allowing for a diagnostic of the CME magnetic field strength. Such a magnetic field diagnostic is important for evaluating the total magnetic energy content of the CME, which is ultimately what drives the eruption. Here, we report on an unusually large source of gyrosynchrotron radiation in the form of a type IV radio burst associated with a CME occurring on 2014-September-01, observed using instrumentation from the Nançay Radio Astronomy Facility. A combination of spectral flux density measurements from the Nançay instruments and the Radio Solar Telescope Network (RSTN) from 300 MHz to 5 GHz reveals a gyrosynchrotron spectrum with a peak flux density at ~1 GHz. Using this radio analysis, a model for gyrosynchrotron radiation, a non-thermal electron density diagnostic using the Fermi Gamma Ray Burst Monitor (GBM) and images of the eruption from the GOES Soft X-ray Imager (SXI), we were able to calculate both the magnetic field strength and the properties of the X-ray and radio emitting energetic electrons within the CME. We find the radio emission is produced by non-thermal electrons of energies >1 MeV with a spectral index of δ ~ 3 in a CME magnetic field of 4.4 G at a height of 1.3 R⊙, while the X-ray emission is produced from a similar distribution of electrons but with much lower energies on the order of 10 keV. We conclude by comparing the electron distribution characteristics derived from both X-ray and radio and show how such an analysis can be used to define the plasma and bulk properties of a CME.

MICROWAVE EMISSION OF SOLAR FLARES: CORONAL MASS EJECTIONS AND SHOCK WAVES

Coronal mass ejections (CMEs) mostly affect the geomagnetic field. These structures are observed and studied with coronagraphic images therefore we don’t see the corona in the plane of the sky and the measurements of the propagation speed for solar disk events are not accessible to coronagraphic observations. This suggests that microwave emission of solar flares that can be attributed to the gyrosynchrotron mechanism of mildly relativistic electrons can be used. In turn, the relationship between coronal shock waves and CMEs also remains unclear. The data set that we use in this study is based on microwave (μ) observations of spectral fluxes Fμ at 8.8 GHz obtained with the Radio Solar Telescope Network for the 124 proton solar events . The correlation coefficient r between the CME velocities VCME and integral fluxes of microwave emission ∫Fμdt achieves of about 0.8 while it does not exceed 0.36 between VCME and the shock wave velocities. It has been found the quite strong correlation between the growth rate of microwave emission and the deceleration of frequency drift in the frequency range of 25-180 GHz (r ≈ 0.66). The obtained results suggest that microwave observation can be used to predict VCME and the shock wave generation occurs in the region of flare energy release.

Solar Radio Burst Statistics and Implications for Space Weather Effects

AbstractSolar radio bursts have the potential to affect space and terrestrial navigation, communication, and other technical systems that are sometimes overlooked. However, over the last decade a series of extreme L band solar radio bursts in December 2006 have renewed interest in these effects. In this paper we point out significant deficiencies in the solar radio data archives of the National Centers for Environmental Information (NCEI) that are used by most researchers in analyzing and producing statistics on solar radio burst phenomena. In particular, we examine the records submitted by the United States Air Force (USAF) Radio Solar Telescope Network (RSTN) and its predecessors from the period 1966 to 2010. Besides identifying substantial missing burst records we show that different observatories can have statistically different burst distributions, particularly at 245 MHz. We also point out that different solar cycles may show statistically different distributions and that it is a mistake to assume that the Sun shows similar behavior in different sunspot cycles. Large solar radio bursts are not confined to the period around sunspot maximum, and prediction of such events that utilize historical data will invariably be an underestimate due to archive data deficiencies. It is important that researchers and forecasters use historical occurrence frequency with caution in attempting to predict future cycles.

Exploring the potential of microwave diagnostics in SEP forecasting: The occurrence of SEP events

Solar energetic particles (SEPs), especially protons and heavy ions, may be a space-weather hazard when they impact spacecraft and the terrestrial atmosphere. Forecasting schemes have been developed, which use earlier signatures of particle acceleration to predict the arrival of solar protons and ions in the space environment of the Earth. The UMASEP (University of MAlaga Solar particle Event Predictor) scheme forecasts the occurrence and the importance of an SEP event based on combined observations of soft X-rays, their time derivative and protons above 10 MeV at geosynchronous orbit. We explore the possibility to replace the derivative of the soft X-ray time history with the microwave time history in the UMASEP scheme. To this end we construct a continuous time series of observations for a 13-month period from December 2011 to December 2012 at two microwave frequencies, 4.995 and 8.8 GHz, using data from the four Radio Solar Telescope Network (RSTN) patrol stations of the US Air Force, and feed this time series to the UMASEP prediction scheme. During the selected period the Geostationary Operational Environmental Satellites (GOES) detected nine SEP events related to activity in the western solar hemisphere. We show that the SEP forecasting using microwaves has the same probability of detection as the method using soft X-rays, but no false alarm in the considered period, and a slightly increased warning time. A detailed analysis of the missed events is presented. We conclude that microwave patrol observations improve SEP forecasting schemes that employ soft X-rays. High-quality microwave data available in real time appear as a significant addition to our ability to predict SEP occurrence.

Spectral Trends of Solar Bursts at Sub-THz Frequencies

Previous sub-THz studies were derived from single-event observations. We here analyze for the first time spectral trends for a larger collection of sub-THz bursts. The collection consists of a set of 16 moderate to small impulsive solar radio bursts observed at 0.2 and 0.4 THz by the Solar Submillimeter-wave Telescope (SST) in 2012 – 2014 at El Leoncito, in the Argentinean Andes. The peak burst spectra included data from new solar patrol radio telescopes (45 and 90 GHz), and were completed with microwave data obtained by the Radio Solar Telescope Network, when available. We critically evaluate errors and uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission, and introduce a new method to obtain a uniform flux scale criterion for all events. The sub-THz bursts were searched during reported GOES soft X-ray events of class C or larger, for periods common to SST observations. Seven out of 16 events exhibit spectral maxima in the range 5 – 40 GHz with fluxes decaying at sub-THz frequencies (three of them associated to GOES class X, and four to class M). Nine out of 16 events exhibited the sub-THz spectral component. In five of these events, the sub-THz emission fluxes increased with a separate frequency from that of the microwave spectral component (two classified as X and three as M), and four events have only been detected at sub-THz frequencies (three classified as M and one as C). The results suggest that the THz component might be present throughout, with the minimum turnover frequency increasing as a function of the energy of the emitting electrons. The peculiar nature of many sub-THz burst events requires further investigations of bursts that are examined from SST observations alone to better understand these phenomena.

On the origin of 140 GHz emission from the 4 July 2012 solar flare

The sub-THz event observed on the 4 July 2012 with the Bauman Moscow State Technical University Radio Telescope RT-7.5 at 93 and 140GHz as well as Kislovodsk and Metsähovi radio telescopes, Radio Solar Telescope Network (RSTN), GOES, RHESSI, and SDO orbital stations is analyzed. The spectral flux between 93 and 140GHz has been observed increasing with frequency. On the basis of the SDO/AIA data the differential emission measure has been calculated. It is shown that the thermal coronal plasma with the temperature above 0.5MK cannot be responsible for the observed sub-THz flare emission. The non-thermal gyrosynchrotron mechanism can be responsible for the microwave emission near 10GHz but the observed millimeter spectral characteristics are likely to be produced by the thermal bremsstrahlung emission from plasma with a temperature of about 0.1MK.

An Interpretation of a Possible Mechanism for the First Ground-Level Enhancement of Solar Cycle 24

It is well known that solar flares and shocks driven by coronal mass ejections (CMEs) are high-energy particle acceleration processes that might cause a high-energy particle event known as a ground-level enhancement (GLE). In this context, we have attempted to understand the processes responsible for the first GLE event (GLE71 17 May 2012 01:50 UT) of Solar Cycle 24. We studied the spatial and spectral data from the Solar Dynamics Observatory (SDO) the Culgoora radio-heliograph, and Wind/WAVES instrument, and analyzed the temporal data of the solar-flare components, the solar radio-flux density, and the electron fluxes from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the Geostationary Operational Environmental Satellite (GOES), the Radio Solar Telescope Network (RSTN), and Wind spacecraft. The flare had two ribbons separated by the neutral line between negative and positive magnetic polarity. Their structure was also almost consistent with the contours of some flare components, which were almost saturated during the flare-peak time. As indicated by the metric–kilometric Type-II burst, and because it extended over a wide heliolongitude (> ≈ 41∘) range, the CME-driven shock was fast enough to cause high-energy particle acceleration at a high altitude in the solar corona. Moreover, the CME and flare-flash phases were aligned along the same direction, which implies that if the CME-driven shock played the leading role in causing the GLE, preceding flare components may have contributed to the shock.

The effect of solar radio bursts on the GNSS radio occultation signals

AbstractSolar radio burst (SRB) is the radio wave emission after a solar flare, covering a broad frequency range, originated from the Sun's atmosphere. During the SRB occurrence, some specific frequency radio wave could interfere with the Global Navigation Satellite System (GNSS) signals and therefore disturb the received signals. In this study, the low Earth orbit‐ (LEO‐) based high‐resolution GNSS radio occultation (RO) signals from multiple satellites (COSMIC, CHAMP, GRACE, SAC‐C, Metop‐A, and TerraSAR‐X) processed in University Corporation for Atmospheric Research (UCAR) were first used to evaluate the effect of SRB on the RO technique. The radio solar telescope network (RSTN) observed radio flux was used to represent SRB occurrence. An extreme case during 6 December 2006 and statistical analysis during April 2006 to September 2012 were studied. The LEO RO signals show frequent loss of lock (LOL), simultaneous decrease on L1 and L2 signal‐to‐noise ratio (SNR) globally during daytime, small‐scale perturbations of SNR, and decreased successful retrieval percentage (SRP) for both ionospheric and atmospheric occultations during SRB occurrence. A potential harmonic band interference was identified. Either decreased data volume or data quality will influence weather prediction, climate study, and space weather monitoring by using RO data during SRB time. Statistically, the SRP of ionospheric and atmospheric occultation retrieval shows ~4% and ~13% decrease, respectively, while the SNR of L1 and L2 show ~5.7% and ~11.7% decrease, respectively. A threshold value of ~1807 SFU of 1415 MHz frequency, which can result in observable GNSS SNR decrease, was derived based on our statistical analysis.

Acceleration of solar cosmic rays and the fine spectral structure of type II radio bursts

On the basis of data, obtained by means of the ground-based solar service RSTN (Radio Solar Telescope Network) and the geostationary satellite system GOES, the relationship between the solar cosmic rays (SCR) intensity I p with the proton energy E p > 1 MeV and parameters of meter-decameter type II radio bursts in the frequency range of 25–180 MHz is studied. The process of proton acceleration by shock waves was characterized by the frequency drift velocity of radio bursts V mII and the relative difference between radio emission frequencies at the first two harmonics b. It is shown that the coefficient of correlation between I p and b increases with E p growing from 0.40 to 0.70, while a similar coefficient between I p and V mII does not exceed 0.30. Indications in favor of the two-stage SCR acceleration model are obtained.