Radio Events Research Articles

Estimation of emission cone wall thickness of Jupiter’s decametric radio emission using stereoscopic STEREO/WAVES observations

Aims. Stereoscopic observations by the WAVES instrument onboard two STEREO spacecraft have been used with the aim of estimating wall thickness of an emission cone of Jovian decametric radio emission (DAM). Methods. Stereoscopic observations provided by STEREO-A and -B facilitate unambiguous recognition of the Jovian DAM in observed dynamic spectra as well as identification of its components (Io DAM or non-Io DAM). The dynamic spectra of radio emissions recorded by STEREO/WAVES have been analyzed using the method of cross-correlation of the radio dynamic spectra. Results. Altogether, 139 radio events, in particular 91 Io- and 48 non-Io-related radio events were observed. The averaged width of the emission cone wall for Io-DAM as well as for non-Io DAM is about 1.1° ± 0.2°. These results are in agreement with previous findings.

The May 1967 great storm and radio disruption event: Extreme space weather and extraordinary responses

AbstractAlthough listed as one of the most significant events of the last 80 years, the space weather storm of late May 1967 has been of mostly fading academic interest. The storm made its initial mark with a colossal solar radio burst causing radio interference at frequencies between 0.01 and 9.0 GHz and near‐simultaneous disruptions of dayside radio communication by intense fluxes of ionizing solar X‐rays. Aspects of military control and communication were immediately challenged. Within hours a solar energetic particle event disrupted high‐frequency communication in the polar cap. Subsequently, record‐setting geomagnetic and ionospheric storms compounded the disruptions. We explain how the May 1967 storm was nearly one with ultimate societal impact, were it not for the nascent efforts of the United States Air Force in expanding its terrestrial weather monitoring‐analysis‐warning‐prediction efforts into the realm of space weather forecasting. An important and long‐lasting outcome of this storm was more formal Department of Defense‐support for current‐day space weather forecasting. This story develops during the rapid rise of solar cycle 20 and the intense Cold War in the latter half of the twentieth century. We detail the events of late May 1967 in the intersecting categories of solar‐terrestrial interactions and the political‐military backdrop of the Cold War. This was one of the “Great Storms” of the twentieth century, despite the apparent lack of large geomagnetically induced currents. Radio disruptions like those discussed here warrant the attention of today's radio‐reliant, cellular‐phone and satellite‐navigation enabled world.

Evidence for magnetic field compression in shocks within the jet of V404 Cyg

We present optical and near-IR linear polarimetry of V404 Cyg during its 2015 outburst and in quiescence. We obtained time resolved r'-band polarimetry when the source was in outburst, near-IR polarimetry when the source was near quiescence and multiple wave-band optical polarimetry later in quiescence. The optical to near-IR linear polarization spectrum can be described by interstellar dust and an intrinsic variable component. The intrinsic optical polarization, detected during the rise of one of the brightest flares of the outburst, is variable, peaking at 4.5 per cent and decaying to 3.5 per cent. We present several arguments that favour a synchrotron jet origin to this variable polarization, with the optical emission originating close to the jet base. The polarization flare occurs during the initial rise of a major radio flare event that peaks later, and is consistent with a classically evolving synchrotron flare from an ejection event. We conclude that the optical polarization flare represents a jet launching event; the birth of a major ejection. For this event we measure a rather stable polarization position angle of -9 degrees E of N, implying that the magnetic field near the base of the jet is approximately perpendicular to the jet axis. This may be due to the compression of magnetic field lines in shocks in the accelerated plasma, resulting in a partially ordered transverse field that have now been seen during the 2015 outburst. We also find that this ejection occurred at a similar stage in the repetitive cycles of flares.

Characteristics of Four Upward-Pointing Cosmic-Ray-like Events Observed with ANITA.

We report on four radio-detected cosmic-ray (CR) or CR-like events observed with the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload. Two of the four were previously identified as stratospheric CR air showers during the ANITA-I flight. A third stratospheric CR was detected during the ANITA-II flight. Here, we report on characteristics of these three unusual CR events, which develop nearly horizontally, 20-30km above the surface of Earth. In addition, we report on a fourth steeply upward-pointing ANITA-I CR-like radio event which has characteristics consistent with a primary that emerged from the surface of the ice. This suggests a possible τ-lepton decay as the origin of this event, but such an interpretation would require significant suppression of the standard model τ-neutrino cross section.

Gr-MRI: A software package for magnetic resonance imaging using software defined radios

The goal of this work is to develop software that enables the rapid implementation of custom MRI spectrometers using commercially-available software defined radios (SDRs). The developed gr-MRI software package comprises a set of Python scripts, flowgraphs, and signal generation and recording blocks for GNU Radio, an open-source SDR software package that is widely used in communications research. gr-MRI implements basic event sequencing functionality, and tools for system calibrations, multi-radio synchronization, and MR signal processing and image reconstruction. It includes four pulse sequences: a single-pulse sequence to record free induction signals, a gradient-recalled echo imaging sequence, a spin echo imaging sequence, and an inversion recovery spin echo imaging sequence. The sequences were used to perform phantom imaging scans with a 0.5Tesla tabletop MRI scanner and two commercially-available SDRs. One SDR was used for RF excitation and reception, and the other for gradient pulse generation. The total SDR hardware cost was approximately $2000. The frequency of radio desynchronization events and the frequency with which the software recovered from those events was also measured, and the SDR’s ability to generate frequency-swept RF waveforms was validated and compared to the scanner’s commercial spectrometer. The spin echo images geometrically matched those acquired using the commercial spectrometer, with no unexpected distortions. Desynchronization events were more likely to occur at the very beginning of an imaging scan, but were nearly eliminated if the user invoked the sequence for a short period before beginning data recording. The SDR produced a 500kHz bandwidth frequency-swept pulse with high fidelity, while the commercial spectrometer produced a waveform with large frequency spike errors. In conclusion, the developed gr-MRI software can be used to develop high-fidelity, low-cost custom MRI spectrometers using commercially-available SDRs.

Observational study of ionospheric irregularities and GPS scintillations associated with the 2012 tropical cyclone Tembin passing Hong Kong

AbstractThis study presents the ionospheric responses observed in Hong Kong to a Typhoon, namely, Tembin, from the aspects of the occurrence of ionospheric irregularities and scintillations, using Global Positioning System (GPS) observations from a ground‐based GPS scintillation monitoring station in Hong Kong and from GPS receivers on board the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. The ionospheric irregularities and scintillations are characterized by the rate of total electron content variation index (ROTI) and the amplitude scintillation index S4, respectively. The typhoon Tembin formed over the western North Pacific during 18–30 August 2012 and approached Hong Kong during 24–27 August 2012 with the closest distance 290 km from Hong Kong at around 17 universal time (UT) on 25 August 2012. The ground‐based observations indicate that in the nighttime period of 20:00–02:00 local time (LT = UT + 8 h) on 26 August when Tembin passed closely to Hong Kong, the ionospheric irregularities and scintillations of GPS signals were observed in the south of Hong Kong, over the area of 13°N ~ 23°N in latitude and 110°E ~ 120°E in longitude. From the COSMIC observations, it shows that the number of radio occultation scintillation events peaks on 26 August 2012 during the passage of Tembin. Without the presence of strong geomagnetic or solar activity, it is suspected that gravity waves might be generated in the lower atmosphere and likely seed the formation of ionospheric plasma irregularities. This work for the first time from Hong Kong observes the sign of coupling between the lower atmosphere and ionosphere in a tropical cyclone event, combining both ground‐ and space‐based GPS observation data.

Classifying RRATs and FRBs

In this paper we consider the fact that the simple criterion used to label fast radio transient events as either fast radio bursts (FRBs, thought to be extragalactic with as yet unknown progenitors) or rotating radio transients (RRATs, thought to be Galactic neutron stars) is uncertain. We identify single pulse events reported in the literature which have never been seen to repeat, and which have been labelled as RRATs, but are potentially mis-labelled FRBs. We examine the probability that such `grey area' events are within the Milky Way. The uncertainty in the RRAT/FRB labelling criterion, as well as Galactic-latitude dependent reporting bias may be contributing to the observed latitude dependence of the FRB rate, in addition to effects such as Eddington bias due to scintillation.

On modelling the Fast Radio Burst population and event rate predictions

Assuming that Fast Radio Bursts (FRBs) are of extragalactic origin, we have developed a formalism to predict the FRB detection rate and the redshift distribution of the detected events for a telescope with given parameters. We have adopted FRB 110220, for which the emitted pulse energy is estimated to be $E_0 = 5.4 \times 10^{33}J$, as the reference event. The formalism requires us to assume models for (1) pulse broadening due to scattering in the ionized inter-galactic medium - we consider two different models for this, (2) the frequency spectrum of the emitted pulse - we consider a power law model $E_{\nu} \propto \nu^{-\alpha}$ with $-5 \leq \alpha \leq 5$, and (3) the comoving number density of the FRB occurrence rate $n(E,w_i,z)$ - we ignore the z dependence and assume a fixed intrinsic pulse width $w_i = 1$ms for all the FRBs. The distribution of the emitted pulse energy $E$ is modelled through (a) a delta-function where all the FRBs have the same energy $E = E_0$ , and (b) a Schechter luminosity function where the energies have a spread around $E_0$. The models are all normalized using the 4 FRBs detected by Thornton et al. (2013). Our model predictions for the Parkes telescope are all consistent with the inferred redshift distribution of the fourteen FRBs detected there to date. We also find that scattering places an upper limit on the redshift of the FRBs detectable by a given telescope; for the Parkes telescope this is $z \sim 2$. Considering the upcoming Ooty Wide Field Array, we predict a FRB detection rate of $\sim 0.01$ to $\sim 10^3$ per day.

A timer-based operating system for ZigBee sensor platforms

In recent years, resource constrained hardware makes the operating system simplicity a most crucial design criterion. The majority of research in such operating systems has focused on the reactive nature of an event-driven kernel. However, the event-based kernel may result in the latency of processing events and erroneous energy profiling. Most battery-driven wireless sensor nodes use the radio event to wake up sleeping nodes, but the radio always consumes more energy than other components during the transmission intervals. The contribution of this paper is that we present EXOS, a timer-driven operating system which can both process periodic events on time and obtain rapid responses to external signals. The system kernel can be easily ported to any other memory-constrained target platforms. EXOS is able to provide the detailed prediction of each component's energy consumption during program execution. The evaluation has demonstrated that EXOS can be practically integrated into wireless sensor networks.

A pilot ASKAP survey of radio transient events in the region around the intermittent pulsar PSR J1107−5907

We use observations from the Boolardy Engineering Test Array (BETA) of the Australian Square Kilometre Array Pathfinder (ASKAP) telescope to search for transient radio sources in the field around the intermittent pulsar PSR J1107-5907. The pulsar is thought to switch between an "off" state in which no emission is detectable, a weak state and a strong state. We ran three independent transient detection pipelines on two-minute snapshot images from a 13 hour BETA observation in order to 1) study the emission from the pulsar, 2) search for other transient emission from elsewhere in the image and 3) to compare the results from the different transient detection pipelines. The pulsar was easily detected as a transient source and, over the course of the observations, it switched into the strong state three times giving a typical timescale between the strong emission states of 3.7 hours. After the first switch it remained in the strong state for almost 40 minutes. The other strong states lasted less than 4 minutes. The second state change was confirmed using observations with the Parkes radio telescope. No other transient events were found and we place constraints on the surface density of such events on these timescales. The high sensitivity Parkes observations enabled us to detect individual bright pulses during the weak state and to study the strong state over a wide observing band. We conclude by showing that future transient surveys with ASKAP will have the potential to probe the intermittent pulsar population.

THEMIS observations and riometry: A data comparison with a view to proxy and prediction

A comparison has been made between radio absorption events observed by riometer at selected times of day and bursts of electrons observed in the midnight sector by THEMIS satellites. The correlation is found to be good for absorption in the noon and midnight sectors but poor around dawn and dusk. For noon and midnight the absorption can be estimated from the THEMIS electron flux to better than a factor of 2 in most cases. In the noon sector the absorption follows the THEMIS event by about 30min on average (though with considerable variation from case to case), but by night the absorption precedes the electron flux by about 8min on average. Thus, the flux at THEMIS can be predicted from the absorption in the night sector, the accuracy being better than a factor of 3 in most cases. The flux observed also depends on the location of the satellite, reducing with increasing distance down the tail. It is estimated that the source of the tail events observed in this study was at about 6Re, and comparisons are made with the established general pattern of the substorm in auroral absorption.

Very low frequency radio events with a reduced intensity observed by the low‐altitude DEMETER spacecraft

AbstractWe present results of a systematic study of unusual very low frequency (VLF) radio events with a reduced intensity observed in the frequency‐time spectrograms measured by the low‐orbiting Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) spacecraft. They occur exclusively on the nightside. During these events, the intensity of fractional hop whistlers at specific frequencies is significantly reduced. These frequencies are usually above about 3.4 kHz (second Earth‐ionosphere waveguide cutoff frequency), but about 20% of events extend down to about 1.7 kHz (first Earth‐ionosphere waveguide cutoff frequency). The frequencies of a reduced intensity vary smoothly with time. We have inspected 6.5 years of DEMETER data, and we identified in total 1601 such events. We present a simple model of the event formation based on the wave propagation in the Earth‐ionosphere waveguide. We apply the model to two selected events, and we demonstrate that the model is able to reproduce both the minimum frequencies of the events and their approximate frequency‐time shapes. The overall geographic distribution of the events is shifted by about 3000 km westward and slightly southward with respect to the areas with high long‐term average lightning activity. We demonstrate that this shift is related to the specific DEMETER orbit, and we suggest its qualitative explanation by the east‐west asymmetry of the wave propagation in the Earth‐ionosphere waveguide.

Introduction to “Comparative Radios”

Introduction to “Comparative Radios” Martin Harries (bio) and Lecia Rosenthal (bio) In Current of Music, a collection of his writings on radio written in English while in American exile, Theodore W. Adorno writes: The author knows of the following fact from his own German experience. In Kronberg, a country place not far from Frankfurt am Main where he often stayed with friends, he had the opportunity of listening to a nightingale which sang very beautifully in the garden. This nightingale was discovered by the Frankfurt Radio Station, and the author and his friends managed to listen to it over the radio when the windows were open. The result was that we were able to hear the radio nightingale a bit earlier than we could hear the real voice because sound takes longer to reach the ear ordinarily through space than by electrical waves. … Thus the “radio voice” creates a strong feeling of immediate presence. It may make the radio event appear even more present than the live event. This feeling of presence necessarily means a feeling of immediacy, too. When we face a radio phenomenon we are actually “present” in that our own presence in time is no different from that of witnesses to the broadcast event. Because of this immediacy, this experience of being present in time, radio always tends to make us forget that it gives us in other respects a mediated phenomenon. (74) Neither the bald reference to fact nor the wobbly science should deceive us: this is almost certainly a fable. Adorno, testing, one might imagine, his unwitting American readers, rewrites one of Immanuel Kant’s fables about the beautiful:1 What do poets praise more highly than the nightingale’s enchantingly beautiful song in a secluded thicket on a quiet summer evening by the soft light of the moon? And yet we have cases where some jovial innkeeper, unable to find such a songster, played a trick—received with greatest satisfaction [initially]—on the guests staying at his inn to enjoy the country air, by hiding in a bush some roguish youngster who (with a reed or rush in his mouth) knew how to copy the song in a way very similar to nature’s. But [End Page 1] as soon as one realizes that it was all deception, no one will long endure listening to this song that before he has considered so charming. (169) The visit to the country, the nightingale, the ersatz nightingale, a form of mediation involving tubes: the central elements of the story from the Critique of Judgment return in Adorno’s roguish imitation of Kant for the age of radio. Adorno’s revision also points to a problem implicit in Kant’s story. “By introducing the possibility of a false or feigned note,” writes Lynn Festa, “Kant’s mock bird catapults the delighted listener into a disenchanted world in which each object must be measured against its potential imitation” (84). In Kant’s tale, the “jovial innkeeper” colludes with the “roguish youngster” to undermine the authority of the beautiful in its tie to nature; in Adorno, the radio team, having somehow “discovered” the nightingale and set up its equipment to record its song, produces a presence that is in some way “even more present” than “the live event.” Adorno tells the story in similar terms a second time in the essay “The Radio Voice,” but draws more sweeping conclusions (in language more recognizably Adorno’s): The real nightingale sounded like her own echo. Such an extreme case reveals a bit of what may well be at the bottom of ordinary radio experience owing to the fact the experienced immediacy is no genuine immediacy: at the same time one knows that this immediacy is a consequence of mechanization and reification and that it may tilt into something disavowing the kind of presence that it promulgates. The presence is the presence of phantasmagoria. (377–78) The “extreme case” of the nightingale reveals that “experienced immediacy is no genuine immediacy”: just as the imitation of the nightingale in Kant, however perfect, produces a simulacrum that no one will find “charming” once the deception has been revealed, so the recorded nightingale produces an...

Multi‐frequency solar observations at Metsähovi Radio Observatory and KAIRA

AbstractWe describe solar observations carried out for the first time jointly with Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) and Aalto University Metshovi Radio Observatory (MRO). KAIRA is new radio antenna array observing the decimeter and meter wavelength range. It is located near Kilpisjärvi, Finland, and operated by the SodankyläGeophysical Observatory, University of Oulu. We investigate the feasibility of KAIRA for solar observations, and the additional benefits of carrying out multi‐instrument solar observations with KAIRA and the MRO facilities, which are already used for regular solar observations. The data measured with three instruments at MRO, and with KAIRA during time period 2014 April–October were analyzed. One solar radio event, measured on 2014 April 18, was studied in detail. Seven solar flares were recorded with at least two of the three instruments at MRO, and with KAIRA during the chosen time period. KAIRA is a great versatile asset as a new Finnish instrument that can also be used for solar observations. Collaboration observations with MRO instruments and KAIRA enable detailed multi‐frequency solar flare analysis. Flare pulsations, flare statistics and radio spectra of single flares can be investigated due to the broad frequency range observations. The Northern locations of both MRO and KAIRA make as long as 15‐hour unique solar observations possible during summer time. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

SOLAR SOURCES OF3He-RICH SOLAR ENERGETIC PARTICLE EVENTS IN SOLAR CYCLE 24

Using high-cadence EUV images obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, we investigate the solar sources of 26 ^3He-rich solar energetic particle events at ≾1 MeV nucleon^(−1) that were well-observed by the Advanced Composition Explorer during solar cycle 24. Identification of the solar sources is based on the association of ^3He-rich events with type III radio bursts and electron events as observed by Wind. The source locations are further verified in EUV images from the Solar and Terrestrial Relations Observatory, which provides information on solar activities in the regions not visible from the Earth. Based on AIA observations, ^3He-rich events are not only associated with coronal jets as emphasized in solar cycle 23 studies, but also with more spatially extended eruptions. The properties of the ^3He-rich events do not appear to be strongly correlated with those of the source regions. As in the previous studies, the magnetic connection between the source region and the observer is not always reproduced adequately by the simple potential field source surface model combined with the Parker spiral. Instead, we find a broad longitudinal distribution of the source regions extending well beyond the west limb, with the longitude deviating significantly from that expected from the observed solar wind speed.

Abstract P1-11-14: Evidence-based programs to reduce breast cancer mortality in Panama City

Abstract In Panama, as in other Latin American countries, breast cancer is the most common cause of cancer-related deaths among women, and is becoming a major public health problem. Breast cancer mortality rates have steadily risen since 2002 and reflect not only breast cancer incidence and risk factors, but also late-stage diagnosis, quality of cancer care and reduced access to health care. Susan G. Komen® developed an evidence-based strategic plan for reducing breast cancer mortality focused on increasing access to breast cancer screening and care. Komen’s approach resulted from an analysis of the breast cancer continuum of care in Panama City, aimed at understanding the factors that determine whether women enter the breast cancer continuum of care, and the barriers that prevent women from completing the continuum. Komen utilized the results of the study to drive programs and develop evaluation plans. We conducted four focus groups and individual interviews with 35 breast cancer survivors living in Panama City to assess the factors that determine access to the breast cancer continuum of care, as well as personal perceptions of breast cancer treatment and follow up. In addition, we held 69 in-depth interviews to capture the community’s perceived barriers in accessing cancer care from three stakeholder groups: public and private medical professionals, non-profits, and private insurers. Interviews and focus groups were audio taped, transcribed and the content analyzed for emergent themes and patterns. Based on the data, we drafted three different paths of breast cancer care depending on the type of health insurance: Seguro Social (Social security system), private insurance, or no insurance. In all scenarios we identified health care system deficiencies within the primary, secondary and tertiary care levels, in particular low medical breast cancer training and lack of delineated referral guidelines. Community level gaps identified include lack of information, awareness, and social support networks. To address these gaps, Komen implemented strategic activities that included a program to fund interventions to conduct awareness campaigns, train primary care medical professionals, and reduce barriers to access breast health and cancer care that in Panama is mostly localized in the capital. Impact was measured using an impact chart based on evidence-based and best practice interventions in the areas of public awareness, community and professional education, and continuum of care services. With an investment of $500,000 over two years we were able to reach 2 million people with breast health and breast cancer messaging through 92 television and 268 radio events, and 2,500 views through social media. We funded a total of 36 medical trainings on standard breast health care guidelines by level of care, protocols and referral processes reaching a total of 1,328 medical providers and 65 community leaders, some from indigenous communities (caciques). Finally, we provided housing assistance to 130 women from rural areas that had traveled to receive breast health and breast cancer services, including treatment and follow-up if needed. Our results show that evidence-based programs provide the opportunity to improve service in areas of most need. Citation Format: Anna Cabanes, Maria Roquebert, Tauane Cruz, Blanca Benaglio, Becky Royer. Evidence-based programs to reduce breast cancer mortality in Panama City [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-11-14.

GPS radio occultation constellation design with the optimal performance in Asia Pacific region

The growing desire for better spatial and also temporal distribution of radio occultation data is a motivation for extensive researches considering either number of GNSS/receiver satellites or better optimization tools resulting in better distributions. This paper addresses the problem of designing a global positioning system-only radio occultation mission with the optimal performance in Asia Pacific region. Constellation Patterns are discussed and 2D-lattice and 3D-lattice flower constellations are adopted to develop a system with circular and elliptical orbits, respectively. A perturbed orbit propagation model leading to significantly more accurate pre-analysis is used. Emphasizing on the spatial and also temporal distribution of radio occultation events for the first time, distribution norm is provided as a volumetric distribution measure using Voronoi diagram concept in a 3D space consisting temporal and spatial intervals. Optimizations are performed using genetic algorithm to determine optimal constellation design parameters by the suitable fitness function and constraints devised. The resulted constellation has been evaluated by a regional comparison to the globally distributed FORMOSAT-3/COSMIC in terms of the distribution norm, number of radio occultation events and also coverage as an additional point-to-point distribution measure. Although it is demonstrated that the optimal 3D-lattice enjoys better performance than FORMOSAT-3, the design approach results in a 2D-lattice flower constellation which is superior to other constellations in regional emphasis of radio occultation events. Its global performance is discussed and it is demonstrated that using multi-GNSS receiver to increase satellites may not guarantee a good distribution of radio occultation data in some aspects.

Unexpected Very Low Frequency (VLF) Radio Events Recorded by the Ionospheric Satellite DEMETER

DEMETER was a low Earth orbiting microsatellite in operation between July 2004 and December 2010. Its scientific objective was the study of ionospheric perturbations in relation to seismic activity and man-made activities. Its payload was designed to measure electromagnetic waves over a large frequency range as well as ionospheric plasma parameters (electron and ion densities, fluxes of energetic charged particles). This paper will show both expected and unusual events recorded by the satellite when it was in operation. These latter events have been selected from the DEMETER database because they are rare or even have never been observed before, because they have a very high intensity, or because they are related to abnormalities of the experiments under particular plasma conditions. Some events are related to man-made radio waves emitted by VLF ground-based transmitters or power line harmonic radiation. Natural waves, such as atypical quasi-periodic emissions or uncommon whistlers, are also shown.

Performance assessment of GPS receivers during the September 24, 2011 solar radio burst event

The sudden outburst of in-band solar radio noise from the Sun is recognized as one of the potential Radio Frequency Interference (RFI) sources that directly impact the performance of Global Navigation Satellite System (GNSS) receivers. On September 24, 2011, the solar active region 1302 unleashed a moderate M7.1 soft X-ray flare associated with a very powerful radio burst at 1415 MHz. The Solar Radio Burst (SRB) event spanned over three distinct episodes of solar radio noise emission that reached the maximum radio flux density of 114,144 Solar Flux Units (SFU) at 13:04:46 UTC. This paper analyzes the impact of September 24, 2011 SRB event on the performance of a significant subset of NAVSTAR Global Positioning System (GPS) receivers located in the sunlit hemisphere. The performance assessment is carried out in terms of Carrier-to-Noise power spectral density ratio (C /N 0 ) degradation, dual-frequency pseudorange measurements availability, pseudorange residual errors, and dual-frequency positioning errors in the horizontal and vertical dimensions. We observed that during the SRB event the GPS C /N 0 is reduced at most by 13 dB on L1 and 24 dB on L2. The C /N 0 degradation caused the loss of lock on GPS L1 and L2 signals and significant code-tracking errors. We noticed that many stations experienced less than four satellite measurements, which are the minimum required number of measurements for position estimation. The deteriorated satellite-receiver geometry due to loss of signal lock and significant code-tracking errors during the solar radio burst event introduced large positioning errors in both the horizontal and vertical dimensions. Rise in vertical positioning error of 303 m and rise in horizontal positioning of 55 m could be noticed during the solar radio burst event.

Fourier Analysis of Radio Bursts Observed with Very High Time Resolution

Numerous solar radio bursts were observed in 2000 - 2001 using the Toru´ nr adio spectrograph with its unique time resolution of 80 microseconds. This high time resolution enables an in-depth analysis of the time evolution of the power spectra and Fourier spectral indices of selected short radio bursts. We analyze the power-spectrum parameters and vari- ability for two millisecond radio dm-spike events and one drifting pulsation structure (DPS) event, for which the structures of the recorded signals were analyzed with an effective time resolution of 0.0008 s in five adjacent frequency bands of their radio spectra. We found that Fourier spectral indices varied rapidly when radio fine structures were recorded. Otherwise they remained close to zero, indicating the presence of noise. For the 10 - 40 Hz frequency interval of the power spectra the mean values of the Fourier spectral indices varied up to −1.51 for the dm-spikes and up to −1.53 for the DPS event. Cross- correlation coefficients of radio fluxes in adjacent frequency bands varied between 0.12 and 0.60 for dm-spikes and between 0.77 and 0.94 for the DPS event. The shortest fine structure found in the studied events lasted 0.001 s. These results are entirely new for dm-radio spikes and confirm a single previous result found for the DPS events. On the basis of our results, we propose that dm-spikes and DPS events are physically similar and that both are signatures of cascades of interacting plas- moids of different sizes.