European Incoherent Scatter Scientific Association Research Articles

Ionospheric upwelling and the level of associated noise at solar minimum

Abstract. We have studied the ionospheric upwelling with a magnitude of above 1013 m−2 s−1 using the data during the European Incoherent Scatter Scientific Association (EISCAT) Svalbard Radar International Polar Year (IPY-ESR) 2007 campaign, which coincides with the solar minimum. The noise level in low-, medium- and high-flux upflows is investigated. We found that the noise level in high-flux upflow is about 93 %, while in the low and medium categories it is 62 % and 80 %, respectively. This shows that robust and stringent filtering techniques must be ensured when analysing incoherent data in order not to introduce bias to the result. Analysis reveals that the frequency of the low-flux upflow events is about 8 and 73 times the medium- and high-flux upflow events, respectively. Seasonal observation shows that the noise level in the upflow classes is predominantly high during winter. The noise is minimal in summer, with a notable result indicating occurrence of actual data above noise in the low-flux class. Moreover, the percentage occurrence of the noise level in the data increases with increasing flux strength, irrespective of the season. Further analysis reveals that the noise level in the local time variation peaked around 17:00–18:00 LT (local time) and minimum around 12:00 LT.

Machine learning with oversampling for space debris classification based on radar cross section

Over the past few years, the likelihood of collision of space objects increases as the quantity of space debris rises. Space debris classification and identification becomes more crucial to space assets security and space situation awareness. Radar cross section (RCS), one of the essential arguments for tracking space debris, was measured by European Incoherent Scatter Scientific Association (EISCAT) and other radar systems. This study investigates the effectiveness of seven machine learning methods employed to address the classification of space objects based on RCS data from European Space Agency (ESA). To tackle the Class-imbalance issue in this study (the ratio of space debris to non-debris is approximately 5:1 in the dataset), three oversampling techniques are employed, including: Synthetic Minority Oversampling Technique (SMOTE), synthetic minority oversampling technique-support vector machine (SMOTE-SVM) and Adaptive Synthetic Sampling (ADASYN). The experiments show that, in the test set, the combination of SVM with SMOTE-SVM oversampling techniques can reach the accuracy of 99.7%, the precision of 98.7% and the recall of 99.4% which is better than the rest of models.

On mechanisms for high-frequency pump-enhanced optical emissions at 557.7 and 630.0 nm from atomic oxygen in the high-latitude F-region ionosphere

Abstract. The EISCAT (European Incoherent Scatter Scientific Association) Heating facility was used to transmit powerful high-frequency (HF) electromagnetic waves into the F-region ionosphere to enhance optical emissions at 557.7 and 630.0 nm from atomic oxygen. The emissions were imaged by several stations of ALIS (Auroral Large Imaging System) in northern Sweden, and the EISCAT UHF incoherent scatter radar was used to obtain plasma parameter values. The ratio of the 557.7 to 630.0 nm column emission rates changed from I5577/I6300≈0.2 for the HF pump frequency f0=6.200 MHz ≈4.6fe to I5577/I6300≈0.5 when f0=5.423 MHz ≲4fe, where fe is the ionospheric electron gyro frequency. The observations are interpreted in terms of decreased electron heating efficiency and thereby weaker enhancement at 630.0 nm for f0=5.423 MHz ≲ 4 fe. The emissions at 557.7 nm are attributed to electron acceleration by upper hybrid waves of metre-scale wavelengths that can be excited with f0=5.423 MHz ≲ 4 fe.

A Comparative Assessment of the Distribution of Joule Heating in Altitude as Estimated in TIE‐GCM and EISCAT Over One Solar Cycle

AbstractDuring geomagnetically active times, Joule (or frictional) heating in the Lower Thermosphere‐Ionosphere is a significant source of thermal energy, greatly affecting density, temperature, composition and circulation. At the same time, Joule heating and the associated Pedersen conductivity are amongst the least known parameters in the upper atmosphere in terms of their quantification and spatial distribution, and their parameterization by geomagnetic parameters shows large discrepancies between estimation methodologies, primarily due to a lack of comprehensive measurements in the region where they maximize. In this work we perform a long‐term statistical comparison of Joule heating as calculated by the NCAR Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) and as obtained through radar measurements by the European Incoherent Scatter Scientific Association (EISCAT). Statistical estimates of Joule heating and Pedersen conductivity are obtained from a simulation run over the 11 year period spanning from 2009 until 2019 and from radar measurements over the same period, during times of radar measurements. The results are statistically compared in different Magnetic Local Time sectors and Kp level ranges in terms of median values and percentiles of altitude profiles. It is found that Joule heating and Pedersen conductivity are higher on average in TIE‐GCM than in EISCAT for low Kp and are lower than EISCAT for high Kp. It is also found that neutral winds cannot account for the discrepancies between TIE‐GCM and EISCAT. Comparisons point toward the need for a Kp‐dependent parameterization of Joule heating in TIE‐GCM to account for the contribution of small scale effects.

History of EISCAT – Part 6: the participation of Japan in the EISCAT Scientific Association

Abstract. In Sect. 1, the original planning of Japanese Svalbard IS (incoherent scatter) radar with phased-array antennas is described. In 1988, this plan was proposed as one of the major projects for the forthcoming Solar–Terrestrial Environment Laboratory, Nagoya University, Japan, to be reorganized by the Research Institute of Atmospherics at Nagoya University. On the other hand, in 1989, UK scientists proposed a plan of polar cap radar with parabolic dish antennas in Longyearbyen to the EISCAT (European incoherent scatter) Council. In Sect. 2, the circumstances leading to Japan's participation in the EISCAT Scientific Association, with details of its processes with strong collaborations with Norwegian scientists and the EISCAT Scientific Association are described. In 1995, Japan participated EISCAT Scientific Association as the seventh member country with funds contributing to the second dish antenna of the EISCAT Svalbard Radar. In Sect. 3, a summary of the EISCAT-related achievement by Japanese scientists is described, where major interests are the lower thermosphere wind dynamics, the magnetosphere–ionosphere–thermosphere coupling, characteristics, and driving mechanisms of ion upflow, electrodynamics of current, electric field and particles, characteristics and production mechanisms of auroras, such as pulsating aurora, and aurora tomography. In Sect. 4, a summary of the scientific collaborations between Japan and Europe, particularly those between Japan and Norway, and hopes for the forthcoming EISCAT_3D and further collaboration with EISCAT community are described.

Model‐Free Approach for Regional Ionospheric Multi‐Instrument Imaging

AbstractThe article proposes a straightforward Kalman filter‐based method for computationally efficient ionospheric electron density multi‐instrument imaging. The approach uses direct ionospheric measurements, such as ionosondes, and general physical assumptions to estimate the uncertainty associated with the previous reconstructed time step. Therefore the method does not require any electron density model of the ionosphere as a background. The uncertainty is represented by an inverse covariance matrix constructed with Gaussian Markov random fields, allowing the problem to be solved directly with relatively high resolution. The experiments utilize measurements from dense ground‐based GNSS and low Earth orbit beacon satellite receiver networks as well as ionosondes. A synthetic simulation verification and real data validation with a specific European Incoherent Scatter Scientific Association incoherent scatter radar measurement campaign is carried out over Northern European sector. The method can be controlled using parameters with probabilistic and physically realistic interpretations that can be applied to both simulated and real‐world data. The results show that the approach is feasible for near real‐time regional ionospheric imaging. Especially, the method can be seen as an expansion to local profile measurements field of view, but with sufficient measurement coverage, it also provides information further away from the specific instrument.

Comparison of the reaction of polar mesosphere winter echoes and polar mesosphere summer echoes to high-frequency heating in terms of modulated characteristics

In this work, for the first time, we have analyzed and compared the responses of polar mesosphere winter echoes (PMWE) and their summer counterpart, polar mesosphere summer echoes (PMSE), to high-frequency (HF) heating in terms of modulated characteristics (i.e., backscatter intensity reduction, recovery, and overshoot). Both PMWE and PMSE observations were from the same site (Tromsø, Norway; 69.6°N, 19.2°E) and radar (EISCAT [European Incoherent Scatter Scientific Association] very high frequency, 224 MHz). The heating patterns of both PMWE and PMSE were found to be similar; however, PMSE was more greatly affected by HF heating. Polar mesosphere summer echoes showed recovery and overshoot more frequently than did PMWE. In addition, the mean recovery and overshoot of PMSE were greater than those of PMWE. The associated electron temperature enhancement was estimated for both PMWE and PMSE and showed that, compared with PMWE, the electron temperature enhancement was more significant in PMSE. The strong heating effects on PMSE may be due to the considerable increase in electron temperature.

History of the Tromsø ionosphere heating facility

Abstract. We present the historical background of the construction of a major ionospheric heating facility, “Heating”, near Tromsø, Norway, in the 1970s by the Max Planck Institute for Aeronomy; we also detail the facility's subsequent operational history to the present. Heating was built next to the European Incoherent Scatter Scientific Association (EISCAT) incoherent scatter (IS) radar facility and in a region with a multitude of diagnostic instruments used to study the auroral region. The facility was transferred to EISCAT in January 1993 and continues to provide new discoveries in plasma physics and ionospheric and atmospheric science to this day. It is expected that Heating will continue operating along with the new generation of IS radar, called EISCAT_3D, when it is commissioned in the near future.

Experimental ELF/VLF Wave Communication With Excitation by Ionosphere Modulated Heating

AbstractIn this study, we present experimental results from the European Incoherent Scatter Scientific Association for communication using extremely low frequency/very low frequency (ELF/VLF) electromagnetic (EM) waves excited via amplitude‐modulated auroral electrojet. EM wave signals with modulation frequencies of 2,017 and 3,517 Hz were encoded by quaternary phase shift keying, and three transmission rates (20, 100, and 400 bps) were selected. By analyzing the ELF/VLF EM wave intensity at the receiver, we found that the relationship between the ELF/VLF wave intensity and natural current intensity was affected by the background ionospheric state. Combined with previously published experimental results from High‐frequency Active Auroral Research Program communications, the relationship between bit error rate (BER) and signal‐to‐noise ratio (Eb/N0) at the receiver was also analyzed. The results showed that when Eb/N0 > 8 dB, BER = 0 and when Eb/N0 < 8 dB, the relationship between BER and Eb/N0 satisfies the complementary error function, and the accurate relationship between them is given via experimental data fitting.

Validation of SSUSI-derived auroral electron densities: comparisons to EISCAT data

Abstract. The coupling of the atmosphere to the space environment has become recognized as an important driver of atmospheric chemistry and dynamics. In order to quantify the effects of particle precipitation on the atmosphere, reliable global energy inputs on spatial scales commensurate with particle precipitation variations are required. To that end, we have validated auroral electron densities derived from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) data products for average electron energy and electron energy flux by comparing them to EISCAT (European Incoherent Scatter Scientific Association) electron density profiles. This comparison shows that SSUSI far-ultraviolet (FUV) observations can be used to provide ionization rate and electron density profiles throughout the auroral region. The SSUSI on board the Defense Meteorological Satellite Program (DMSP) Block 5D3 satellites provide nearly hourly, 3000 km wide high-resolution (10 km×10 km) UV snapshots of auroral emissions. These UV data have been converted to average energies and energy fluxes of precipitating electrons. Here we use those SSUSI-derived energies and fluxes as input to standard parametrizations in order to obtain ionization-rate and electron-density profiles in the E region (90–150 km). These profiles are then compared to EISCAT ground-based electron density measurements. We compare the data from two satellites, DMSP F17 and F18, to the Tromsø UHF radar profiles. We find that differentiating between the magnetic local time (MLT) “morning” (03:00–11:00 MLT) and “evening” (15:00–23:00 MLT) provides the best fit to the ground-based data. The data agree well in the MLT morning sector using a Maxwellian electron spectrum, while in the evening sector using a Gaussian spectrum and accounting for backscattered electrons achieved optimum agreement with EISCAT. Depending on the satellite and MLT period, the median of the differences varies between 0 % and 20 % above 105 km (F17) and ±15 % above 100 km (F18). Because of the large density gradient below those altitudes, the relative differences get larger, albeit without a substantially increasing absolute difference, with virtually no statistically significant differences at the 1σ level.

On the relationship of energetic particle precipitation and mesopause temperature

Abstract. Energetic particle precipitation (EPP) has the potential to change the neutral atmospheric temperature in the mesopause region. However, recent results are inconsistent, leaving the mechanism and the actual effect still unresolved. In this study we have searched for electron precipitation events and investigated a possible correlation between D-region electron density enhancements and simultaneous neutral temperature changes. The rotational temperature of the excited hydroxyl (OH) molecules is retrieved from the infrared spectrum of the OH airglow. The electron density is monitored by the European Incoherent Scatter Scientific Association (EISCAT) Svalbard Radar. We use all available experiments from the International Polar Year (IPY) in 2007–2008 until February 2019. Particle precipitation events are characterized by rapid increases in electron density by a factor of 4 at an altitude range of 80–95 km, which overlaps with the nominal altitude of the infrared OH airglow layer. The OH airglow measurements and the electron density measurements are co-located. Six of the 10 analysed electron precipitation events are associated with a temperature decrease of 10–20 K. Four events were related to a temperature change of less than 10 K. We interpret the results in terms of the change in the chemical composition in the mesosphere. Due to EPP ionization the population of excited OH at the top of the airglow layer may decrease. As a consequence, the airglow peak height changes and the temperatures are probed at lower altitudes. The observed change in temperature thus depends on the behaviour of the vertical temperature profile within the airglow layer. This is in agreement with conclusions of earlier studies but is, for the first time, constructed from electron precipitation measurements as opposed to proxies. The EPP-related temperature change recovers very fast, typically within less than 60 min. We therefore further conclude that this type of EPP event reaching the mesopause region would only have a significant impact on the longer-term heat balance in the mesosphere if the lifetime of the precipitation was much longer than that of an EPP event (30–60 min) found in this study.

Analysis of Observations near the Fourth Electron Gyrofrequency Heating Experiment in EISCAT

We present the observations of the artificial ionospheric heating experiment of EISCAT (European Incoherent Scatter Scientific Association) on 22 February 2012 in Tromsø, Norway. When the pump is operating near the fourth electron gyrofrequency, the UHF radar observation shows some strong enhancements in electron temperature, electron density, ion line, and the outshifted plasma lines. Based on some existing theories, we find the following: first, Langmuir waves scattering off lower hybrid density fluctuations and strong Langmuir turbulence (SLT) in the Zakharov model cannot completely explain the outshifted plasma lines, but the data suggest that this phenomenon is related to the cascade of the pump wave and should be researched further; second, the spatiotemporal consistency between the enhancement in electron density/electron temperature reaches up to three to four times that of the undisturbed state and HF-enhanced ion lines (HFILs) suggest that SLT excited by parametric instability plays a significant role in superthermal electron formation and electron acceleration; third, some enhancements in HFILs and HF-induced plasma lines (HFPLs) are generated by parametric decay instability (PDI) during underdense heating in the third cycle, we suggest that this is due to the existence of a second cut-off in the upper hybrid dispersion relation as derived from a kinetic description.

Planetary radar science case for EISCAT 3D

Abstract. Ground-based inverse synthetic aperture radar is a tool that can provide insights into the early history and formative processes of planetary bodies in the inner solar system. This information is gathered by measuring the scattering matrix of the target body, providing composite information about the physical structure and chemical makeup of its surface and subsurface down to the penetration depth of the radio wave. This work describes the technical capabilities of the upcoming 233 MHz European Incoherent Scatter Scientific Association (EISCAT) 3D radar facility for measuring planetary surfaces. Estimates of the achievable signal-to-noise ratios for terrestrial target bodies are provided. While Venus and Mars can possibly be detected, only the Moon is found to have sufficient signal-to-noise ratio to allow high-resolution mapping to be performed. The performance of the EISCAT 3D antenna layout is evaluated for interferometric range–Doppler disambiguation, and it is found to be well suited for this task, providing up to 20 dB of separation between Doppler northern and southern hemispheres in our case study. The low frequency used by EISCAT 3D is more affected by the ionosphere than higher-frequency radars. The magnitude of the Doppler broadening due to ionospheric propagation effects associated with traveling ionospheric disturbances has been estimated. The effect is found to be significant but not severe enough to prevent high-resolution imaging. A survey of lunar observing opportunities between 2022 and 2040 is evaluated by investigating the path of the sub-radar point when the Moon is above the local radar horizon. During this time, a good variety of look directions and Doppler equator directions are found, with observations opportunities available for approximately 10 d every lunar month. EISCAT 3D will be able to provide new, high-quality polarimetric scattering maps of the nearside of the Moon with the previously unused wavelength of 1.3 m, which provides a good compromise between radio wave penetration depth and Doppler resolution.

Auroral‐Enhanced Plasma Lines by Suprathermal Electrons Observed by EISCAT

AbstractPlasma lines (PLs) observed by the European Incoherent Scatter Scientific Association (EISCAT) incoherent scatter radar (ISR) data set during the recent solar maximum 2014 are investigated. To statistically analyze the PLs in the EISCAT data set, we develop an algorithm for the automatic extraction of naturally enhanced PLs from the ISR spectra. Two typical types of auroral‐enhanced PLs at high latitude, namely, secondary electron and electron beam, are analyzed based on this PL extraction algorithm. Our results show that PL enhancements originating from secondary electrons and electron beams present evident magnetic local time dependence. Moreover, the statistical study indicates that the PL enhancements are correlated with the geomagnetic and solar activities. These results can provide insights into solar wind‐magnetosphere‐ionosphere coupling mechanisms.

GLONASS Observation of Artificial Field‐Aligned Plasma Irregularities Near Magnetic Zenith During EISCAT HF Experiment

AbstractWe report on simultaneous observation of artificial plasma density irregularities near the magnetic zenith (MZ) by incoherent scatter radar and GNSS satellite in the high latitude. During an EISCAT (European Incoherent Scatter Scientific Association) HF heating experiment, a GLONASS satellite signal intersected the disturbed ionospheric volume along the local magnetic field lines. The satellite signal amplitude and phase were simultaneously perturbed when the electron temperature increased in the F region through O‐mode HF waves. The field‐aligned irregularities (FAIs) and associated density perturbations are most significantly found in the MZ direction. The growth of FAI reached the saturation level in 30 s while large‐scale electron density perturbation on the order of 0.1 TECU developed in a few minutes. The observed density perturbations agree well with recent numerical studies of FAI generation due to the thermal self‐focusing process.

CSES observations of ELF wave radiation excited by the EISCAT heater

Modulation heating of the ionosphere using high-power high-frequency (HF) radio waves can generate an extremely low frequency (ELF) radiation source in the ionosphere, such as amplitude-modulation (AM) heating of the auroral electrojet or using two HF radio waves to illuminate the same region of the ionosphere to form beat-wave (BW) modulation. We first present observations of ELF waves received on the China seismo-electromagnetic satellite (CSES) and on the ground simultaneously, which were excited in the European Incoherent Scatter Scientific Association (EISCAT) modulation heating experiment carried out alternately in the AM and BW modes. When the CSES passed over the EISCAT heater, ELF waves excited in the AM and BW modes were received successfully by an electric field detector on board. The comparison of the received results between the satellite and the ground demonstrates that although the intensity of the ELF signals excited in the BW mode is far lower than that in the AM mode on the ground, the ratio of ELF wave intensities between the satellite and the ground in the BW mode is significantly larger than that in the AM mode. According to the experimental results, the propagation characteristics are simulated using the full-wave method when the ELF radiation sources are located in the D and F regions in the ionosphere.

ELF/VLF Communication Experiment by Modulated Heating of Ionospheric Auroral Electrojet at EISCAT

Amplitude modulation high-frequency (HF) radio waves at extremely low frequencies (ELF, 0.3-3 kHz) or very low frequencies (VLF, 3-30 kHz), heating the ionosphere, can nonlinearly modulate the auroral electrojet to produce ELF/VLF waves for long-distance communication. This article presents the results of the first ELF/VLF communication experiments being conducted at Tromsø, where the European Incoherent Scatter Scientific Association (EISCAT) HF facility is located. The ELF/VLF waves from the ionosphere are modulated by quaternary phase shift keying (QPSK) and used for communication. The ELF signals of 2017 Hz at 20 and 100 b/s, as well as VLF signals of 3517 Hz at 20, 100, and 400 b/s, received by a ground-based receiver (15 km away from the heater) were decoded, albeit with a high bit error rate (BER) for 3517 Hz at 20 b/s. With the decoding principle of QPSK, we attempted to find a solution to reduce the BER for future communication experiments. Based on the results of the ground experiment, the transmitted signals of 2017 Hz at 20 b/s were selected in the China Seismo-Electromagnetic Satellite (CSES) reception experiments. In a first, we demonstrate that ELF communication signals generated by the amplitude modulation heating of the ionosphere have been successfully received by the satellite and the ground-based receiver. These experimental results confirm that the ELF/VLF waves radiated by amplitude modulation heating of the auroral electrojet can be used for long-distance communication in future.

A New Technique for Investigating Dust Charging in the PMSE Source Region

AbstractA new technique for investigating dust charging in the PMSE (polar mesospheric summer echoes) source region is proposed and discussed in this paper. The first high‐frequency (HF) modulation of the PMSE with varying pump power was employed during a recent experimental campaign at EISCAT (European Incoherent Scatter Scientific Association). Two experiment setups including HF pump power stepping as well as quasi‐continuous power sweeping were used. The experiment was designed based on a computational model capable of simulation of PMSE evolution during HF pump modulation in order to develop a new approach for studying the dust charging process in the PMSE source region. The charge state of dust particles along with background dusty plasma parameters is estimated using the experimental and computational results. A detailed future experimental design based on background dusty‐plasma parameters is proposed.

On the Production of Ionospheric Irregularities Via Kelvin‐Helmholtz Instability Associated with Cusp Flow Channels

AbstractWe present a multi‐instrument multiscale study of a channel of enhanced, inhomogeneous flow in the cusp ionosphere occurring on November 30, 2014. We provide evidence that strong Global Navigation Satellite System (GNSS) phase scintillations indices (σϕ>0.5 rad) can arise from such events, indicating that they are important in the context of space weather impacts on technology. We compare in detail two‐dimensional maps of ionospheric density, velocity, and temperatures obtained by the European Incoherent Scatter Scientific Association Svalbard Radar with scintillation indices detected from a network of four GNSS receivers around Svalbard and examine the different sources of free energy for irregularity creation. We observe that the strongest phase scintillations occur on the poleward side of the flow channel in a region of sheared plasma motion and structured low‐energy particle precipitation. As inhomogeneous plasma flows are evident in our observations, we perform a quantitative, nonlinear analysis of the Kelvin–Helmholtz instability (KHI) and its impact on phase scintillations using numerical simulations from the first principles‐based Geospace Environment Model of Ion‐Neutral Interactions and Satellite‐beacon Ionospheric‐scintillation Global Model of the upper Atmosphere. Using representative values consistent with the radar data, we show that KHI can efficiently create density structures along with considerable scintillations and is thus likely to contribute significantly under similar conditions, which are frequent in the cusp.

Multi-frequency SuperDARN radar observations of the modulated ionosphere by high-power radio-waves at EISCAT

This paper presents the first joint observations of multi-frequency SuperDARN (Super Dual Auroral Radar Network) radar of the heated ionosphere by high-power high-frequency (HF) ground-based radio-waves along with the stimulated electromagnetic emissions (SEE) measurements. The unique heating experiment design at EISCAT (The European Incoherent Scatter Scientific Association) including fine frequency stepping through the fourth electron gyro-frequency (4fce) provided the opportunity to directly determine the plasma waves responsible for SuperDARN radar echoes. Past experiments using a unique Kodiak SuperDARN receiver in Alaska with capability of data recording over a large bandwidth of frequencies different from the radar transmission frequency was able to detect some radar echoes due to pump-excited plasma waves. However, a precise characterization of these waves could not be reached in the past. Comparison of the behavior of the SEE data measured on the ground besides the multi-frequency SuperDARN observations above the heated ionosphere at EISCAT has shown a good correlation with the characteristics of upper-hybrid (UH)/electron Bernstein (EB) waves excited through parametric decay instability. The ray tracing model based on the EISCAT dynasonde data of the background ionospheric parameters has been used in order to determine the natural ionospheric effects on the propagation path of 9.9 MHz, 13.2 MHz, and 16.6 MHz signals associated with SuperDARN radar. By providing a more direct connection between SuperDARN echoes and the associated SEE measurements, this new technique potentially provides more quantitative characterization of plasma waves generated during ionospheric heating.