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Decametric radio emissions (DAM) originating in Jupiter’s polar magnetosphere ought to originate on magnetic field lines at the local electron gyrofrequency. The Io-related DAM have received the most attention since the 1980’s. The maximum frequency of these emissions ought to be bounded by the maximum magnetic field strength above the footprint of the instantaneous Io Flux Tube (IFT). However, there remains a lack of agreement between the frequency extent of Io-related decameter radiation and the frequency extent predicted by Jovian magnetic field models. Here, we analyze peak frequencies and source locations of Io and non-Io-related DAM observed by Juno during the prime mission (~10,600 events) and show how the latest magnetic field model can accommodate and control Io-DAM. We note that the observed peak frequencies appear to be truncated at 37 MHz although the magnetic field in the northern hemisphere would allow events to 55 MHz at some longitudes. Lower frequencies than the ones allowed by the magnetic field are consistently observed for most of the Io’s longitude. To reconcile this discrepancy, we analyze the upper electron density limit distribution along the magnetic field lines, the possible existence of plasma cavities and the locations in the magnetosphere where the extraordinary mode is no longer achieved. For this, we make use of beaming angles of Io-DAM and the geometry of the Jovian magnetic field.

The Juno Waves instrument measured plasma waves associated with Ganymede's magnetosphere during its flyby on 7 June, day 158, 2021. Three distinct regions were identified including a magnetotail/wake, and nightside and dayside regions in the main magnetosphere distinguished by their electron densities and associated variability. The main magnetosphere includes electron cyclotron harmonic emissions including a band at the upper hybrid frequency, as well as whistler-mode chorus and hiss. These waves likely interact with energetic electrons in Ganymede’s magnetosphere by pitch angle scattering and/or accelerating the electrons. The magnetotail/wake is accentuated by low-frequency turbulence and electrostatic solitary waves. Radio emissions observed before and after the flyby likely have their source in Ganymede’s magnetosphere.

The possibility to apply passive radar sounding techniques to the Jovian icy moons, making use of Jupiter’s strong decametric emissions (DAMs), has recently garnered large research interest. In this article, we propose a radar sounding simulation approach being able to simulate and compare passive and active acquisitions for a given scenario. The proposed simulator is based on the Stratton–Chu integral used with the linear phase approximation on triangular facets. The external field is modeled with plane waves, the direction, polarization, and amplitude of which can be freely chosen. The time-domain dependence can be either synthetically generated (e.g., Gaussian white noise) or taken from experimental measurements (e.g., waveforms recorded by a radio telescope observing Jupiter). For passive sounding, both autocorrelation and cross-correlation processing are considered. Validation tests were conducted on a series of ideal digital elevation models (DEMs), such as flat surfaces and subsurfaces, or Gaussian rough surfaces, and a good agreement with the existing literature was obtained. To illustrate the capabilities of the proposed simulator, we conducted additional more realistic experiments of radar sounding simulations, where we use both white noise and Jovian waveforms recorded by the LWA1 radio telescope.

International audience

We present multi-instrument Juno observations on day-of-year 86, 2017 that link particles and fields in Jupiter’s polar magnetosphere to transient UV emissions in Jupiter’s northern auroral region known as dawn storms. Juno ranged from 42ºN - 51ºN in magnetic latitude and 5.8 – 7.8 jovian radii (1 RJ = 71,492 km) during this period. These dawn storm emissions consisted of two separate, elongated structures which extended into the nightside, rotated with the planet, had enhanced brightness (up to at least 1.4 megaRayleigh) and high color ratios. The color ratio is a proxy for the atmospheric penetration depth and therefore the energy of the electrons that produce the UV emissions. Juno observed electrons and ions on magnetic field lines mapping to these emissions. The electrons were primarily field-aligned, bi-directional, and, at times, exhibited sudden intensity decreases below ∼10 keV coincident with intensity enhancements up to energies of ∼1000 keV, consistent with the high color ratio observations. The more energetic electron distributions had characteristic energies of ∼160 – 280 keV and downward energy fluxes (∼70 – 135 mW/m2) that were a significant fraction needed to produce the UV emissions for this event. Magnetic field perturbations up to ∼0.7% of the local magnetic field showing evidence of upward and downward field-aligned currents, whistler mode waves, and broadband kilometric radio emissions were also observed along Juno’s trajectory during this timeframe. These high latitude observations show similarities to those in the equatorial magnetosphere associated with dynamics processes such as interchange events, plasma injections, and/or tail reconnection.

In 1979, the Voyager spacecraft arrived at Jupiter. Amongst their rich array of discoveries, they identified bright bursts of radio emission at kHz frequencies1, often called quasi-periodic (QP) bursts, and discovered Jupiter’s ultraviolet (UV) aurora2 - the most powerful aurora in the Solar System3. The same year that the Voyager spacecraft explored the Jovian system, the Einstein X-ray Observatory took the first X-ray images of Jupiter4 and discovered that planets can also produce bright and dynamic X-ray aurora5,6. Over the subsequent decades, these distinct multi-waveband emissions have all been observed to pulse with quasi-periodic regularity7–10. Here, we combine simultaneous observations by the Juno spacecraft with the X-ray and UV observatories: XMM-Newton, Chandra and the Hubble Space Telescope. These observations show that the radio, UV and X-ray pulses are all synchronised, beating in time together. Further, they reveal that the X-ray and radio pulses share an identical 42.5 minute periodicity with simultaneously measured compression-mode Ultra Low Frequency (ULF) waves in Jupiter’s outer magnetosphere11. ULF waves are known to modulate wave-particle interactions that can cause electron and ion precipitation, providing a physically consistent explanation for the observed simultaneous ion and electron emissions. The unification of Jupiter’s X-ray, UV and radio pulsations and their connection to ULF waves provides fundamental and potentially universal insights into the redistribution of energy in magnetised space environments.

The Juno spacecraft has been orbiting Jupiter since July 2016 providing stunning new information about the planet and its environment. The new magnetic field model, JRM09, with much improved accuracy near the planet, provides the basis for a better understanding of Io-related decametric radio emissions and implications for auroral processes. Here, we study Io-related DAM events observed by the Juno Waves instrument to estimate the beaming angle, the resonant electron energy and radio source location by forward modeling. The JRM09 magnetic field model is used to better constrain the location and observability of the radio emissions, and characterize the loss cone-driven electron cyclotron maser instability. We obtained good agreement between synthetic and observed arcs. The estimated beaming cone half-angles range from 33° to 85° and the obtained resonant electron energies are up to 23 times higher than previously proposed. Additionally, we quantitatively analyze the higher likelihood of observing groups of arcs originating in the northern hemisphere relative to those originating in the southern hemisphere. This is primarily a consequence of the asymmetry of the magnetic field geometry, observer location, and pitch angles of the electrons at the equator.

International audience; We report the first in situ observations of electron measurements at a Europa footprint tail (FPT) crossing in the auroral region. During its 12th science perijove pass, Juno crossed magnetic field lines connected to Europa's FPT. We find that electrons in the range ~0.4 to ~25 keV, with a characteristic energy of 3.6 ± 0.5 keV, precipitate into Jupiter's atmosphere to create the footprint aurora. The energy flux peaks at ~36 mW/m2, while the peak ultraviolet (UV) brightness is estimated at 37 kR. We estimate the peak electron density and temperature to be 17.3 cm-3 and 1.8 ± 0.1 keV, respectively. Using magnetic flux shell mapping, we estimate that the radial width of the interaction at Europa's orbit spans roughly 3.6 ± 1.0 Europa radii. In contrast to typical Io FPT crossings, the instrument background caused by penetrating energetic radiation (> ~5-10 MeV electrons) increased during the Europa FPT crossing.

The Juno mission is providing stunning new information about Jupiter and its environment. A new magnetic field model (JRM09) with much improved accuracy near the planet provides the basis for a better understanding of Io-related decametric radio emissions (DAM) and implications for auroral processes. Here, we selected Io-related DAM events observed by the Juno Waves instrument to shed light into the beaming angle, the resonant electron energy and radio source location by forward modeling. We use the JRM09 model to better constrain the location and observability of DAM, and characterize the loss cone-driven electron cyclotron maser instability. We obtained good agreement between synthetic and observed arcs with calculated beaming angles ranging from 33° to 85° and resonant electron energies up to 23 times higher than previously proposed. In addition, through a quantitative analysis, we provide an explanation regarding the higher likelihood of observing groups of arcs originating in the northern hemisphere relative to those originating in the southern hemisphere. This is primarily a consequence of the asymmetry of the magnetic field geometry, observer location, and pitch angles of the electrons at the equator. Note: This page provides the Juno Waves data and output values of the forward modeling of the Io-related DAM emissions discussed in Martos et al. (2020), Journal ofGeophysical Research Planets. Please, read the Readme file for details about the format.&nbsp

We present Juno observations between 03:00 to 06:00 UT on day-of-year 86, 2017 that link electrons in Jupiter's polar magnetosphere to images of transient, enhanced UV emissions in Jupiter's dawn a...

International audience; Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Previous studies focused on case analyses and/or greater than 30-keV energy electrons. Here for the first time we provide a comprehensive evaluation of Jovian auroral electron characteristics over the entire relevant range of energies (~100 eV to ~1 MeV). The focus is on the first eight perijoves providing a coarse but complete System III view of the northern and southern auroral regions with corresponding UV observations. The latest magnetic field model JRM09 with a current sheet model is used to map Juno's magnetic foot point onto the UV images and relate the electron measurements to the UV features. We find a recurring pattern where the 3- to 30-keV electron energy flux peaks in a region just equatorward of the main emission. The region corresponds to a minimum of the electron characteristic energy (J. Outside that region, the >100-keV electrons contribute to most (>~70-80%) of the total downward energy flux and the characteristic energy is usually around 100 keV or higher. We examine the UV brightness per incident energy flux as a function of characteristic energy and compare it to expectations from a model.

Jupiter’s ultraviolet (UV) aurora, the most powerful and intense in the solar system, is caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Electrons from ~50 eV to ~100 keV are characterized over the auroral regions by the Jovian Auroral Distributions Experiment (JADE) on Juno. Investigating the characteristics of electron distributions at these energies is critical for understanding the source population for the electrons that produce Jupiter’s UV aurora and the mechanisms that accelerated them to keV and MeV energies. In this study, we present a survey of electron distributions and moments derived from JADE in Jupiter’s polar magnetosphere. We quantify the electron properties (e.g. density and temperature) and explore similarities and differences in their distributions over several Juno perijove passes, focusing on regions near the main emission.

The electrodynamic coupling between Io and Jupiter gives rise to wave‐particle interactions across multiple spatial scales. Here we report observations during Juno’s 12th perijove (PJ) high‐latitude northern crossing of the flux tube connected to Io’s auroral footprint. We focus on plasma wave measurements, clearly differentiating between MHD, ion, and electron scales. We find (i) evidence of Alfvén waves undergoing a turbulent cascade, suggesting Alfvénic acceleration processes together with observations of bi‐directional, broadband electrons; (ii) intense ion cyclotron waves with an estimated heating rate that is consistent with the generation of ion conics reported by Clark et al. (in prep); and (iii) whistler‐mode auroral hiss radiation excited by field‐aligned electrons. Such high‐resolution wave and particle measurements provide an insight into satellite interactions in unprecedented detail. We further anticipate that these spatially well‐constrained results can be more broadly applied to better understand processes of Jupiter’s main auroral oval.

Observations of energetic charged particles associated with Io’s footprint (IFP) tail, and likely within or very near the Main Alfvén Wing, during Juno’s 12th perijove (PJ) crossing show evidence of intense proton acceleration by wave‐particle heating. Measurements made by Juno/JEDI reveal proton characteristics that include pitch angle distributions concentrated along the upward loss cone, broad energy distributions that span ~50 keV to 1 MeV, highly structured temporal/spatial variations in the particle intensities, and energy fluxes as high as ~100 mW/m2. Simultaneous measurements of the plasma waves and magnetic field suggest the presence of ion cyclotron waves and transverse Alfvénic fluctuations. We interpret the proton observations as upgoing conics likely accelerated via resonant interactions with ion cyclotron waves. These observations represent the first measurements of ion conics associated with moon‐magnetosphere interactions, suggesting energetic ion acceleration plays a more important role in the IFP tail region than previously considered.

Electrical currents in atmospheric lightning strokes generate impulsive radio waves in a broad range of frequencies, called atmospherics. These waves can be modified by their passage through the plasma environment of a planet into the form of dispersed whistlers1. In the Io plasma torus around Jupiter, Voyager 1 detected whistlers as several-seconds-long slowly falling tones at audible frequencies2. These measurements were the first evidence of lightning at Jupiter. Subsequently, Jovian lightning was observed by optical cameras on board several spacecraft in the form of localized flashes of light3–7. Here, we show measurements by the Waves instrument8 on board the Juno spacecraft9–11 that indicate observations of Jovian rapid whistlers: a form of dispersed atmospherics at extremely short timescales of several milliseconds to several tens of milliseconds. On the basis of these measurements, we report over 1,600 lightning detections, the largest set obtained to date. The data were acquired during close approaches to Jupiter between August 2016 and September 2017, at radial distances below 5 Jovian radii. We detected up to four lightning strokes per second, similar to rates in thunderstorms on Earth12 and six times the peak rates from the Voyager 1 observations13. The Waves instrument on board the Juno spacecraft has detected ~1,600 lightning strokes in roughly 1 year of close approaches to Jupiter, indicated by low-dispersion rapid whistlers much shorter than those detected by Voyager 1 in Io’s plasma torus.

With the aid of the radio and plasma wave (Waves) instrument onboard the Juno spacecraft, the first scientific close encounter to Jupiter (Perijove 1) of Juno led to an opportunity to perform direction finding measurements of the intense Jovian broadband kilometric (bKOM) radiation at 10 to 142 kHz, two escaping continuum radiation (ECR) events at 9 to 22 kHz, and two narrowband kilometric (nKOM) radiation events at 45–112 kHz. We conclude that the northern bKOM radio sources are localized on M-shell=50–60 field lines where M-shell is similar to L-shell for non-dipolar fields. The beam cone half-angle varies from 40∘ to 55∘. By intersecting the wave k vector with the Jovian centrifugal equator, two ECR sources are located inside and outside of 11–12 RJ, and two nKOM sources are found between 11 and 20 RJ. These source frequencies and locations can be used for plasma diagnostics in Jupiter's inner magnetosphere.

Synoptic decametric (DAM) radio observations at Jupiter were made in a broad Jovicentric latitudinal range of −21∘ to +15∘ by the Juno polar orbiting spacecraft from 21 June to 10 December, 2016. We investigated the occurrence probability of non-Io-related DAM. At 19.5 MHz, as Juno's latitude varies from +15∘ to −21∘, a peak of non-Io-B occurrence probability at 175∘ System III central meridian longitude (CML) gradually shifts in longitude to 140∘ CML. Also, another peak occurs at 110∘ CML between −15∘ and −9∘, merging into the bottom edge of the former peak. This J-shaped feature is similarly seen at 16.5 MHz. Using the Jovian magnetic field models, the fixed hollow cone model can reasonably account for the J-shaped structure for radio sources traced along active magnetic flux tubes onto Jupiter's surface projected at about 135∘–149∘ System III longitude. Moreover, these non-Io-B spectral profiles extend from 13.5 to 23.5 MHz.

International audience; Using Juno plasma and wave and magnetic observations (JADE and Waves and MAG instruments), the generation mechanism of the Jovian hectometric radio emission is analyzed. It is shown that suitable conditions for the cyclotron maser instability (CMI) are observed in the regions of the radio sources. Pronounced loss cone in the electron distributions are likely the source of free energy for the instability. The theory reveals that sufficient growth rates are obtained from the distribution functions that are measured by the JADE-Electron instrument. The CMI would be driven by upgoing electron populations at 5-10 keV and 10-30° pitch angle, the amplified waves propagating at 82°-87° from the B field, a fraction of a percent above the gyrofrequency. Typical e-folding times of 10-4 s are obtained, leading to an amplification path of 1000 km. Overall, this scenario for generation of the Jovian hectometric waves differs significantly from the case of the auroral kilometric radiation at Earth.

Two well-defined Jovian decametric radio arcs were observed at latitudinal separations of 11 ∘ –16 ∘ from the Juno spacecraft near Jupiter and the Nancay Decameter Array (NDA) at Earth on 17 May and 25 August 2016. These discrete arcs are from the so-called A source covering both Io-related and non-Io-related emissions. By measuring the wave arrival time at two distant observers with propagation time correction, the remaining delay times are 92.8 ± 1.3 min for the first arc and 116.0 ± 1.2 min for the second arc. This implies that both radio sources are not controlled by the orbital motion of Io but Jupiter's rotation itself. The geometrical information for Juno and NDA and the loss cone-driven electron cyclotron maser instability theory provide these radio sources that are located at about 173 ∘ ± 10 ∘ in system III longitude projected onto Jupiter's north surface and imply resonant electron energy ranges from 0.5 to 11 keV.

The Juno Waves instrument detected a new broadband plasma wave emission (~50 Hz to 40 kHz) on 27 August 2016 as the spacecraft passed over the low-altitude polar regions of Jupiter. We investigated the characteristics of this emission and found similarities to whistler mode auroral hiss observed at Earth, including a funnel-shaped frequency-time feature. The electron cyclotron frequency is much higher than both the emission frequency and local plasma frequency, which is assumed to be ~20–40 kHz. The E/cB ratio was about three near the start of the event and then decreased to one for the rest of the period. A correlation of the electric field spectral density with the flux of an upgoing 20 to 800 keV electron beam was found, with a correlation coefficient of 0.59. We conclude that the emission is propagating in the whistler mode and is driven by the energetic upgoing electron beam.

We compare electron and UV observations mapping to the same location in Jupiter's northern polar region, poleward of the main aurora, during Juno perijove 5. Simultaneous peaks in UV brightness and electron energy flux are identified when observations map to the same location at the same time. The downward energy flux during these simultaneous observations was not sufficient to generate the observed UV brightness; the upward energy flux was. We propose that the primary acceleration region is below Juno's altitude, from which the more intense upward electrons originate. For the complete interval, the UV brightness peaked at ~240 kilorayleigh (kR); the downward and upward energy fluxes peaked at 60 and 700 mW/m2, respectively. Increased downward energy fluxes are associated with increased contributions from tens of keV electrons. These observations provide evidence that bidirectional electron beams with broad energy distributions can produce tens to hundreds of kilorayleigh polar UV emissions., Key Points Simultaneous peaks are observed in electron energy flux and UV brightness when they map to same location in Jupiter's polar region at the same timeUpward greater than downward electron energy fluxes are observed, suggesting that primary acceleration region may be below ~1.5 jovian radiiDownward energy fluxes able to produce tens to hundreds of kilorayleigh polar UV emissions are identified; increases in energy flux due to tens of keV electrons

One of the most intriguing discoveries of Juno is the quasi-systematic detection of upgoing electrons above the auroral regions. Here we discuss a by-product of the most energetic component of this population: a contamination resembling bar codes in the Juno-UVS images. This pattern is likely caused by bursts of ∼10 MeV electrons penetrating the instrument. These events are mostly detected when Juno’s magnetic footprint is located poleward of the main emission relative to the magnetic pole. The signal is not periodic, but the bursts are typically 0.1–1 s apart. They are essentially detected when Juno-UVS is oriented toward Jupiter, indicating that the signal is due to upgoing electrons. The event detections occur between 1 and 7 Jovian radii above the 1-bar level, suggesting that the electron acceleration takes place close to Jupiter and is thus both strong and brief.

International audience

The Juno spacecraft successfully entered Jupiter orbit on 5 July 2016. One of Juno’s primary objectives is to explore Jupiter’s polar magnetosphere for the first time. An obvious major aspect of this exploration includes remote and in-situ observations of Jupiter’s auroras and the processes responsible for them. To this end, Juno carries a suite of particle, field, and remote sensing instruments. One of these instruments is a radio and plasma wave instrument called Waves, designed to detect one electric field component of waves in the frequency range of 50 Hz to 41 MHz and one magnetic field component of waves in the range of 50 Hz to 20 kHz. Juno’s first perijove pass with science observations occurred on 27 August 2016. This paper presents some of the first observations of the Juno Waves instrument made during that first perijove. Among radio emissions, kilometric, hectometric, and decametric emissions were observed. From a vantage point at high latitudes, many of Jupiter’s auroral radio emissions appear as V-shaped emissions in frequency–time space with vertices near the electron cyclotron frequency where the emissions intensify. In fact, we present observations suggesting Juno flew through or close to as many as five or six sources of auroral radio emissions during its first perijove. Waves made in-situ observations of plasma waves on auroral field lines such as whistler–mode hiss, a common feature of terrestrial auroral regions. We also discuss observations of dust at the equator and lightning whistlers observed over mid-latitudes.

Lightning has been detected on Jupiter by all visiting spacecraft through night-side optical imaging and whistler (lightning-generated radio waves) signatures1–6. Jovian lightning is thought to be generated in the mixed-phase (liquid–ice) region of convective water clouds through a charge-separation process between condensed liquid water and water-ice particles, similar to that of terrestrial (cloud-to-cloud) lightning7–9. Unlike terrestrial lightning, which emits broadly over the radio spectrum up to gigahertz frequencies10,11, lightning on Jupiter has been detected only at kilohertz frequencies, despite a search for signals in the megahertz range 12 . Strong ionospheric attenuation or a lightning discharge much slower than that on Earth have been suggested as possible explanations for this discrepancy13,14. Here we report observations of Jovian lightning sferics (broadband electromagnetic impulses) at 600 megahertz from the Microwave Radiometer 15 onboard the Juno spacecraft. These detections imply that Jovian lightning discharges are not distinct from terrestrial lightning, as previously thought. In the first eight orbits of Juno, we detected 377 lightning sferics from pole to pole. We found lightning to be prevalent in the polar regions, absent near the equator, and most frequent in the northern hemisphere, at latitudes higher than 40 degrees north. Because the distribution of lightning is a proxy for moist convective activity, which is thought to be an important source of outward energy transport from the interior of the planet16,17, increased convection towards the poles could indicate an outward internal heat flux that is preferentially weighted towards the poles9,16,18. The distribution of moist convection is important for understanding the composition, general circulation and energy transport on Jupiter. Observations of broadband emission from lightning on Jupiter at 600 megahertz show a lightning discharge mechanism similar to that of terrestrial lightning and indicate increased moist convection near Jupiter’s poles.

Juno's first perijove science observations were carried out on 27 August 2016. The 90° orbit inclination and 4163 km periapsis altitude provide the first opportunity to explore Jupiter's polar magnetosphere. A radio and plasma wave instrument on Juno called Waves provided a new view of Jupiter's auroral radio emissions from near 10 kHz to ~30 MHz. This frequency range covers the classically named decametric, hectometric, and broadband kilometric radio emissions, and Juno observations showed much of this entire spectrum to consist of V-shaped emissions in frequency-time space with intensified vertices located very close to the electron cyclotron frequency. The proximity of the radio emissions to the cyclotron frequency along with loss cone features in the energetic electron distribution strongly suggests that Juno passed very close to, if not through, one or more of the cyclotron maser instability sources thought to be responsible for Jupiter's auroral radio emissions.

International audience; We compare observations from the Juno/Waves radio experiment with simulations of radio «arcs» in the time-frequency plane resulting from the Io-Jupiter interaction, performed with the ExPRES code. We identify the hemisphere of origin of the observed arcs directly from simulations and confirm this identification through comparison with Juno, Nançay, and Wind observations. The occurrence and shape of observed arcs are well modeled, at low latitudes with their usual shapes as seen from Earth, as well as at high latitudes with longer, bowl-shaped, arcs observed for the first time. Predicted emission is actually observed only when the radio beaming angle θ = (k,B) ≥ 70° ± 5°, providing new constraints on the generation of the decameter emission by the Cyclotron Maser Instability. Further improvements of ExPRES are outlined, which will then be applied to Juno and Earth-based observations of radio emissions induced by other Galilean satellites or associated to the main auroral oval.

International audience; Rapid progress currently takes place in the field of low-frequency radio astronomy in the meter-decameter-hectometer range of wavelengths. It is caused by a radical modernization of the existing radio telescopes, creation of a new generation of instruments, space-borne observations, and by the development of research on all classes of astrophysical objects, including the Solar System. On the other hand, a range of difficulties specific to low-frequency radio astronomy is known, which are caused by technical, methodological, and physical limitations. An effective strategy for overcoming these difficulties is based on synchronous observations using several radio telescopes separated by distances from a few to several thousand kilometers. This provides an opportunity to reduce and identify radio interference and the influence of the propagation media, to increase the sensitivity and resolution, and to solve many problems with higher efficiency. In recent years such simultaneous observations were carried out for the Sun, Jupiter, Saturn, interplanetary medium, pulsars, exoplanets, and transients using the radio telescopes UTR-2, URAN, GURT, NDA, NenuFAR, LOFAR and other. Parallel observations with the space missions WIND, STEREO, Cassini and Juno also facilitate improvement of the quality and reliability of low-frequency radio astronomical experiments.

In the version of this Letter originally published, in the second sentence of the last paragraph before the Methods section the word ‘altitudes’ was mistakenly used in place of the word ‘latitudes’. The sentence has now been corrected accordingly to: ‘Low-dispersion class 1 events indicate that low-density ionospheric regions predominantly occur in the northern hemisphere at latitudes between 20° and 70°.’

The Jupiter encounter by the Cassini spacecraft in late 2000 and early 2001 unveiled persistent properties of Jupiter's hectometric (HOM) radiation originating along auroral magnetic field lines in the polar regions. One of the unique properties of the HOM dynamic spectrum, known as attenuation lanes, appears as rotationally modulated, well-defined regions of lowered intensity, flanked by regions of enhancement. These lanes seem to be the result of refraction of radio waves in a high-density medium–either caused by Case (i) enhanced density in the magnetic L-shell connected to Io's orbit or Case (ii) in the Io plasma torus itself or both. In this paper, we investigate the HOM ray paths of 0.5–3.0 MHz emissions with various cone half-angles in the continuous radio longitudes generating at the magnetic L-value equal to 30. We use bi-kappa particle distributions to derive diffusive equilibrium distributions of density in the Io plasma torus. The enhanced density irregularities along the Io flux shell “ribbon” region can be described with a Gaussian density distribution of a maximum density n[0] and breadth (half-width of the distribution across the flux shell) σ. As a result, we found that the interpretation of Case (i) can be accounted for by the attenuation lanes which appear for all cone half-angles, and the reasonable flux shell density n[0] is, on top of specific latitude-dependent density from the diffusive equilibrium model, estimated as 100 cm[−3] with the half-width σ = 5.0 Io radii.

The dataset of Northern Hemisphere EASE-Grid weekly snow cover and sea-ice extent (U.S. National Snow and Ice Data Center) for the period September 1972–August 2000 is analyzed to examine the possible influence of recent global warming on the seasonal change of snow cover in the Northern Hemisphere. It is found that the total snow-cover area in the 1980s and 1990s is diminished by 36106 km2, and the length of snow-cover season is reduced by 2 –3 weeks, as compared with the 1970s. In general, the contribution from earlier snowmelt is greater than that from delayed snow accumulation. In addition, the maximum snow-cover area during January–February has gradually decreased by about 36106 km2 within the two decades. Geographically, the rate of decrease of snow-cover duration is 50.1 week per year (wpy) in the high-latitude regions such as the Siberian Plains and Northwest Territories of Canada and 40.2 wpy in the high-elevation regions such as the Scandinavian Peninsula, Tibetan Plateau and Rocky Mountains. The earlier snowmelt in the high-elevation regions suggests that the snowfall amounts there are decreasing owing to global warming.

掘削土留工に用いる地下連続壁は, 施工精度や品質の向上ならびに経済性の観点から, 近年構造物の本体に利用されることが多く設計法も制定された. 構造物の本体に利用された場合には, 部材は軸方向鉄筋が多段に配置された形状となるが, このような部材でのせん断設計手法を確認するために, 梁状模型試験体を用いた静的一方向載荷試験を実施して, せん断補強鉄筋が無い場合のせん断破壊性状やせん断耐力について実験的な研究を行った. 軸方向鉄筋の配置段数や鉄筋量とせん断破壊性状との関係について, 実験により得られた結果を報告するとともに, せん断耐力算定手法を提案した.