The high‐power HF (high‐frequency) facility (commonly known as Heating) near Tromsø, Norway, which is an essential part of the European Incoherent Scatter Scientific Association, has been upgraded in ...certain key areas in recent years. It is one of only four similar facilities in the world operating at present. An updated description of the facility is given, together with scientific motivation and some results. The main high‐power parts such as transmitters, feed‐system, and antennas remain essentially the same as built in the late 1970s. The improvements are in the areas of radio frequency waveform generation, computer control, and monitoring. In particular, fast stepping in frequency is now possible, an important aspect in examining features close to harmonics of the electron gyrofrequency. One antenna array has been modified to allow reception to implement an HF radar mode for mesospheric and magnetospheric probing. More realistic modeling of the antenna gain gives improved estimates of the total effective radiated power for both wanted and unwanted circular polarizations. Results are presented by using these new capabilities, but their full scientific potential has yet to be achieved.
Key Points
The EISCAT ionospheric heating facility near Tromsø, Norway, has been upgraded in recent years
A high‐power HF radar mode has been implemented to investigate the mesosphere and magnetosphere
Fast frequency stepping is routinely done with interesting results
Active ionospheric experiments using high-power, high-frequency transmitters, “heaters”, to study plasma processes in the ionosphere and magnetosphere continue to provide new insights into ...understanding plasma and geophysical proceses. This review describes the heating facilities, past and present, and discusses scientific results from these facilities and associated space missions. Phenomena that have been observed with these facilities are reviewed along with theoretical explanations that have been proposed or are commonly accepted. Gaps or uncertainties in understanding of heating-initiated phenomena are discussed together with proposed science questions to be addressed in the future. Suggestions for improvements and additions to existing facilities are presented including important satellite missions which are necessary to answer the outstanding questions in this field.
Autoantibodies directed against cytosolic 5'-nucleotidase 1A have been identified in many patients with inclusion body myositis. This retrospective study investigated the association between ...anticytosolic 5'-nucleotidase 1A antibody status and clinical, serological and histopathological features to explore the utility of this antibody to identify inclusion body myositis subgroups and to predict prognosis.
Data from various European inclusion body myositis registries were pooled. Anticytosolic 5'-nucleotidase 1A status was determined by an established ELISA technique. Cases were stratified according to antibody status and comparisons made. Survival and mobility aid requirement analyses were performed using Kaplan-Meier curves and Cox proportional hazards regression.
Data from 311 patients were available for analysis; 102 (33%) had anticytosolic 5'-nucleotidase 1A antibodies. Antibody-positive patients had a higher adjusted mortality risk (HR 1.89, 95% CI 1.11 to 3.21, p=0.019), lower frequency of proximal upper limb weakness at disease onset (8% vs 23%, adjusted OR 0.29, 95% CI 0.12 to 0.68, p=0.005) and an increased prevalence of excess of cytochrome oxidase deficient fibres on muscle biopsy analysis (87% vs 72%, adjusted OR 2.80, 95% CI 1.17 to 6.66, p=0.020), compared with antibody-negative patients.
Differences were observed in clinical and histopathological features between anticytosolic 5'-nucleotidase 1A antibody positive and negative patients with inclusion body myositis, and antibody-positive patients had a higher adjusted mortality risk. Stratification of inclusion body myositis by anticytosolic 5'-nucleotidase 1A antibody status may be useful, potentially highlighting a distinct inclusion body myositis subtype with a more severe phenotype.
We report observations of stimulated electromagnetic emission (SEE) induced by high power high frequency (HF) radio waves near the third electron gyroharmonic (3fce ${f}_{\mathrm{ce}}$) at European ...Incoherent Scatter Radar (EISCAT). It is discovered that stimulated Brillouin scattering (SBS) spectrum behaves similarly as spectral ion lines of the incoherent scatter radar (ISR) for HF pumping frequency above 3fce ${f}_{\mathrm{ce}}$. The SBS spectral width shows correlation with electron to ion temperature ratio Te/Ti. A new inversion method is proposed by incorporating the SBS spectral width within an artificial neural network approach to achieve electron temperature inversion for ionospheric turbulent plasmas. This work provides a potential new technique to diagnose parameters in the modified ionosphere when the ISR is not available.
Plain Language Summary
Nonlinear interaction of high‐power electromagnetic waves and magnetized plasmas produces a plethora of fundamental phenomena. Stimulated electromagnetic emissions (SEEs) arises from nonlinear interaction and induces plasma turbulence observable by incoherent scatter radars (ISR). It is important to compare SEE and ISR spectral lines for understanding nonlinear physics in the resonance regime. The SEE‐based methods may provide complimentary diagnostic tools to the traditional ISR theory. In addition, the SEE‐based inversion theory and method is still lacking due to nonlinear wave‐wave and wave‐particle interaction. The physical correlation between SEEs and ISR spectra will provide benefit for better inversion techniques. This work reports experimental observation and parameter inversion of stimulated Brillouin scatter (SBS) at EISCAT (European Incoherent Scatter Radar). We successfully discover similarity between the ISR ion lines and SBS near the third electron gyroharmonic by high power radio waves at EISCAT. A new diagnostic technique based on SEEs have been developed using physical model and an artificial neural network approach. The inversion of SEEs overcomes the non‐Maxwellian limitations on ISR measurements. These observations demonstrate a physical intrinsic correlation between ISR ion and SBS lines, which provides possibilities for developing new inversion techniques based on SBS in comparison with well‐known ISR theory.
Key Points
Discovery of similarity between high frequency‐induced stimulated Brillouin scattering (SBS) and incoherent scatter radar spectrum
Intelligent stimulated electromagnetic emission inversion architecture proposed by incorporating physical insights within an artificial neural network approach
Novel ionospheric electron temperature inversion based on SBS and downshifted maximum spectral lines
Observations of secondary radiation, stimulated electromagnetic emission (SEE), produced during ionospheric modification experiments using ground-based, high-power, high-frequency (HF) radio waves ...are considered. The High Frequency Active Auroral Research Program (HAARP) facility is capable of generating narrowband SEE in the form of stimulated Brillouin scatter (SBS) and stimulated ion Bernstein scatter (SIBS) in the SEE spectrum. Such narrowband SEE spectral lines have not been reported using the European Incoherent Scatter (EISCAT) heater facility before. This work reports the first EISCAT results of narrowband SEE spectra and compares them to SEE previously observed at HAARP during electron gyro-harmonic heating. An analysis of experimental SEE data shows observations of emission lines within 100 Hz of the pump frequency, interpreted as SBS, during the 2012 July EISCAT campaign. Experimental results indicate that SBS strengthens as the pump frequency approaches the third electron gyro-harmonic. Also, for different heater antenna beam angles, the CUTLASS radar backscatter induced by HF radio pumping is suppressed near electron gyro-harmonics, whereas electron temperature enhancement weakens as measured by EISCAT/UHF radar. The main features of these new narrowband EISCAT observations are generally consistent with previous SBS measurements at HAARP.
This work reports a holistic experimental investigation of stimulated Brillouin scattering (SBS) features and electron temperature inversion near the third electron gyroharmonic 3fce using the ...European Incoherent Scatter (EISCAT) heating facility. The evolution of SBS features including spectral offset, width, and power varies asymmetrically near 3fce. The asymmetries among SBS, electron temperature, and high frequency‐enhanced ion lines are clearly exhibited for pumping above f0 ≥ 3fce. Electron temperature Te at the resonance regime has been retrieved from the measured SBS spectra based on the wave matching theory. The inversion results by SBS are consistent with measurement by the EISCAT UHF incoherent scatter radar (ISR) at the resonance altitude. The comparison of electron temperature Te and ion temperature Ti between SBS and ISR enlightens great potentials for developing realistic ionospheric diagnostic technique.
Key Points
Clearly, SBS dynamics and spectral features are characterized near third electron gyroharmonics at EISCAT
Qualitative comparison of electron temperature inversion based on SBS agrees with ISR measurement
The asymmetries of SBS and DM are closely correlated with enhanced ion lines and electron temperature near 3fce
The experimental phenomena involving the changes in electron temperature and electron density as a function of pump frequency during an ionospheric heating campaign at European Incoherent Scatter ...near Tromsø, Norway, are reported. When the pump frequency is slightly above the fifth electron gyrofrequency, the UHF radar observation shows some apparent enhancements over a wide altitude range in radar echo, ion line, and electron density respectively, which are apparently altitude independent and consistent temporally with the upshifting and spread of plasma line around the reflection altitude. However, they do not, in fact, correspond to true increase in electron density. Based on some existing theories, some discussions are presented to try to explain the above enhancements and the upshifting and spread of plasma line. Even so, the mechanism remains to be determined. In addition, the observation also shows some enhancements in electron temperature as a function of pump frequency around the reflection altitude of the pump, which are dependent on the behavior of dispersion of the upper hybrid wave near the fifth electron gyrofrequency.
Key Points
UHF radar observed enhancements in electron density with an altitude extent do not, in fact, correspond to a true increase in electron density
The upshifting and spread of plasma lines above pump frequency shows the correlation in heating cycle with the above enhancements
The enhancement in electron temperature occurring as a function of pump frequency around the reflection altitude of the pump
The ultrahigh‐frequency observation during an ionospheric heating experiment on 11 March 2014 at the European Incoherent Scatter Scientific Association Tromsø site illustrated a remarkable extension ...of observing altitudes of the enhanced plasma line and the ion line, implying that the enhanced ion acoustic wave and Langmuir wave should satisfy the Bragg condition within the extending altitude range. An analysis shows that the dependence of the wave number of the traveling ion acoustic wave on the profiles of enhanced electron temperature and ion mass, as are expected from the dispersion relation of the ion acoustic wave, leads to the extension of observing altitudes of the enhanced ion line. In addition, the altitude extension of the enhanced plasma line is dependent mainly on the profile of the electron density, although it is not independent of the profile of the electron temperature. Considering a small gradient profile of electron density, however, the enhanced electron temperature, as well as the thermal conduction along the magnetic field, may lead to the altitude extension of the enhanced plasma line.
Key Points
Enhanced plasma line and ion lines were observed by UHF ISR within the extending altitude range, where Bragg condition should be satisfied
Within the altitude range, electron temperature and ion mass compensate each other so that ion acoustic wave satisfies Bragg condition
For a small gradient profile of density, temperature and density compensate each other so that Langmuir wave satisfies Bragg condition
We have compared radar observations of polar mesospheric summer echoes (PMSEs) modulated by artificial electron heating, at frequencies of 224 MHz (EISCAT VHF) and 56 MHz (MORRO). We have ...concentrated on 1 day of observation, lasting ~ 3.8 h. The MORRO radar, with its much wider beam, observes one or more PMSE layers all the time while the VHF radar observes PMSEs in 69% of the time. Statistically there is a clear difference between how the MORRO and the VHF radar backscatter reacts to the heater cycling (48 s heater on and 168 s heater off). While MORRO often reacts by having its backscatter level increased when the heater is switched on, as predicted by Scales and Chen (2008), the VHF radar nearly always sees the "normal" VHF overshoot behaviour with an initial rapid reduction of backscatter. However, in some heater cycles we do see a substantial recovery of the VHF backscatter after its initial reduction to levels several times above that just before the heater was switched on. For the MORRO radar a recovery during the heater-on phase is much more common. The reaction when the heater was switched off was a clear overshoot for nearly all VHF cases but less so for MORRO. A comparison of individual curves for the backscatter values as a function of time shows, at least for this particular day, that in high layers above ~ 85 km height, both radars see a reduction of the backscatter as the heater is switched on, with little recovery during the heater-on time. These variations are well described by present models. On the other hand, the backscatter in low layers at 81–82 km can be quite different, with modest or no reduction in backscatter as the heater is switched on, followed by a strong recovery for both radars to levels several times above that of the undisturbed PMSEs. This simultaneous, nearly identical behaviour at the two very different radar frequencies is not well described by present modelling.
The behavior of polar mesospheric summer echoes (PMSEs) during an electron precipitation event is investigated by including dusty plasma effects for the first time. The observational data recorded ...with the very high frequency (224 MHz) and ultrahigh frequency (930 MHz) radars at the European Incoherent SCATter Scientific Association on 10 and 11 July 2012 are presented. The observed radar echoes show that the PMSEs are both correlated and anticorrelated with the increased electron density associated with electron precipitation events on the two consecutive days. The experimental observations are compared with numerical simulations of the temporal evolution of PMSE with different background dusty plasma parameters during the electron precipitation event. Specifically, the effect of dust radius, dust density, recombination/photoionization rates, photo‐detachment current, and electron density enhancement ratio on the behavior of a PMSE layer and the associated dust charging process in the course of electron precipitation events is studied. It is observed that the ratio of electron density fluctuation amplitude δne to the plasma density (ne) plays a critical role in the appearance/disappearance of the layer. The simulation results revealed that the existence of PMSE is mainly determined by dust radius and dust density. The dusty plasma parameters associated with each event are estimated. The condensation nuclei of the ice particles such as proton hydrate clusters (H+(H2O)n) or meteoric smoke particles can be determined by employing the microphysical models along with the dusty plasma simulations. This can resolve any discrepancy in the description of the observed phenomena.
Key Points
The first comprehensive study of PMSE behavior in the presence of electron precipitation events is presented using observations and modeling
The PMSE strength is mostly governed by background dusty plasma parameters such as dust radius and dust density
Photoemission current and dust fluctuation amplitude produced by neutral turbulence have a great impact on PMSE existence and strength
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