References of "Yao, Zhonghua"
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See detailOrigin and triggers of the 1-hour electron pulsations in the Saturnian system
Palmaerts, Benjamin ULiege; Burkholder, B.; Delamere, P. A. et al

Conference (2019, June 07)

Phenomena displaying a periodicity of around one hour have been frequently observed in Saturn's magnetosphere during the Cassini era. In particular, flux of energetic electrons can exhibit 1-hour quasi ... [more ▼]

Phenomena displaying a periodicity of around one hour have been frequently observed in Saturn's magnetosphere during the Cassini era. In particular, flux of energetic electrons can exhibit 1-hour quasi-periodic pulsations. While these pulsations have been well characterized, their origin and the processes triggering them remained uncertain at the end of the Cassini mission. Using long imaging sequences of the auroral emissions at Saturn, we report the first direct observational evidence that the 1-hour periodicities arise from a global 1-hour oscillation of the Kronian magnetosphere. This natural oscillation acts independently of the local magnetospheric conditions and can have multiple triggering processes. Many 1-hour quasi-periodic electrons were encountered close to the magnetopause, suggesting that magnetopause processes could trigger them, such as magnetic reconnection and Kelvin-Helmholtz (KH) instabilities. We now report simultaneous presence of KH instabilities and 1-hour electron pulsations, supporting this scenario. Pulsed electrons are also encountered much deeper in the magnetosphere and may originate from reconnection in the magnetodisk, on both the day and night sides of the magnetosphere. [less ▲]

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See detailA nearly corotating long lasting auroral spiral at Saturn
Palmaerts, Benjamin ULiege; Yao, Zhonghua ULiege; Sergis, N. et al

Poster (2019, June 04)

The main ultraviolet auroral emission at Saturn consists of multiple structures of various sizes forming a discontinuous ring of emissions around Saturn’s poles. For decades, it is known that the main ... [more ▼]

The main ultraviolet auroral emission at Saturn consists of multiple structures of various sizes forming a discontinuous ring of emissions around Saturn’s poles. For decades, it is known that the main emission is occasionally organized in a global spiral surrounding the pole. In August 2016, the Ultraviolet Imaging Spectrograph (UVIS) on board the Cassini spacecraft proceeded to a 7h-long imaging of Saturn’s northern aurora. During this observing sequence, the main emission displayed a spiral wrapping around the pole by more than 370° in longitude. The spiral was in rotation around the pole at ~90% of rigid corotation, which is an unusually high velocity for extended auroral structures. A spiral was again observed during a shorter UVIS sequence, sixteen hours after the end of the first sequence. Simultaneously to the first UVIS sequence, imaging of the energetic neutral atom (ENA) emissions revealed a hot plasma population in the same local time sector as the extremity of the UV spiral. The leading edge of the plasma population follows the spiral structure around the planet. This correspondence suggests that the presence of the hot plasma distorted the magnetospheric current system, resulting in the spiral shape of the main emission. Furthermore, simultaneous in-situ measurements of the ion fluxes exhibit enhancements recurring every ~10.5 hours. The nearly corotating aurora, ENA emissions and ions revealed by this multi-instrument dataset are likely three signatures of a magnetosphere-ionosphere coupling current system and of the associated hot plasma population corotating with the planet. [less ▲]

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See detailTIN-TIN in Xi-Zang
Yao, Zhonghua ULiege

Scientific conference (2019, February 04)

Io is the most active object in solar system, which domains the plasma source for the massive Jovian magnetosphere. To understand how Io’s geological activities impact Jovian system, a two-telescope ... [more ▼]

Io is the most active object in solar system, which domains the plasma source for the massive Jovian magnetosphere. To understand how Io’s geological activities impact Jovian system, a two-telescope project is proposed, named as Telescope for Io Nebula 1 and 2 (TinTin). TinTin will inherit many technical specifications from ULg-led SPECULOOS project, and will choose the same type of 1-m telescope. TinTin 1 will monitor a small region surrounding Io by several to tens of Io radius, while TinTin 2 will resolve a large area surrounding Jupiter at the scale of a few to hundreds of Jupiter radii. This project will have multiple filters, which allows us to understand the dynamics of different chemical species from Io’s atmosphere escape. The major scientific goals for this project is to understand how Io’s atmosphere escape evolves from small scale (few Io radii) to medium (few Jupiter radii) and large (hundred Jupiter radii) scale, and their impact to Jupiter’s magnetosphere-ionosphere coupling dynamics. [less ▲]

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See detailWaves in Kinetic-Scale Magnetic Dips: MMS Observations in the Magnetosheath
Yao, S. T.; Shi, Q. Q.; Yao, Zhonghua ULiege et al

in Geophysical Research Letters (2019)

Kinetic-scale magnetic dips (KSMDs), with a significant depression in magnetic field strength, and scale length close to and less than one proton gyroradius, were reported in the turbulent plasmas both in ... [more ▼]

Kinetic-scale magnetic dips (KSMDs), with a significant depression in magnetic field strength, and scale length close to and less than one proton gyroradius, were reported in the turbulent plasmas both in recent observation and numerical simulation studies. These KSMDs likely play important roles in energy conversion and dissipation. In this study, we present observations of the KSMDs that are labeled whistler mode waves, electrostatic solitary waves, and electron cyclotron waves in the magnetosheath. The observations suggest that electron temperature anisotropy or beams within KSMD structures provide free energy to generate these waves. In addition, the occurrence rates of the waves are higher in the center of the magnetic dips than at their edges, implying that the KSMDs might be the origin of various kinds of waves. We suggest that the KSMDs could provide favorable conditions for the generation of waves and transfer energy to the waves in turbulent magnetosheath plasmas. ©2018. American Geophysical Union. All Rights Reserved. [less ▲]

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See detailEvolution of the Subauroral Polarization Stream Oscillations during the Severe Geomagnetic Storm on 20 November 2003
He, Fei; Zhang, Xiao-Xin; Wang, Wenbin et al

in Geophysical Research Letters (2019)

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See detailStudy Of The Energy Budget During Isolated Auroral Substorms
Matar, Jessy ULiege; Hubert, Benoît ULiege; Yao, Zhonghua ULiege et al

Conference (2018, December 11)

The solar atmosphere permanently releases ionized material forming the solar wind, which carries the frozen-in interplanetary magnetic field (IMF). When the solar wind reaches the space environment of the ... [more ▼]

The solar atmosphere permanently releases ionized material forming the solar wind, which carries the frozen-in interplanetary magnetic field (IMF). When the solar wind reaches the space environment of the Earth, the IMF and the geomagnetic field can reconfigure their topology in the process of magnetic reconnection. Geomagnetic field lines are therefore opened by the interplanetary medium and dragged anti-sunward by the solar wind flow, which gives the Earth magnetosphere an elongated shape. This process results in the accumulation of open magnetic flux and energy in the geomagnetic tail. Eventually, when a significant amount of open magnetic flux has been accumulated and convected downtail, intense magnetic reconnection also occurs inside of the magnetotail, in the central plasma sheet, and the magnetic field lines return to a closed configuration, which reduces the amount of open magnetic flux. This flux closure process releases a significant amount of energy often estimated to be of the order 10^15 - 10^16 J stored in the tail, which can trigger auroral substorms, as a result of the solar wind - magnetosphere interaction. The released energy is distributed between the ionosphere, the ring current, the plasma sheet, and the formation of a plasmoid. In this work, we combine data from the ESA Cluster and the NASA IMAGE spacecraft to investigate three reconnection events occurring in 2001. We compare in-situ measurement from Cluster and auroral FUV imaging from IMAGE complemented by SuperDARN radar measurement of the ionospheric convection. The auroral hemispheric power is computed using the IMAGE-FUV images of the electron and proton aurora. The amount of open geomagnetic flux is estimated using the imaging of the proton aurora and the magnetic reconnection rates are derived from both missions and the SuperDARN data. We analyze the energy circulation by assessing the energy conversion and dissipation for each individual process during different substorm periods. We compare the hemispheric power, open magnetic flux and reconnection rates and search for a possible relation between them. [less ▲]

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See detailFlying through a Dawn Storm : an analysis of Juno-UVS images during PJ11
Bonfond, Bertrand ULiege; Gladstone, G. R.; Grodent, Denis ULiege et al

Poster (2018, December 11)

Auroral dawn storms at Jupiter are spectacular brightenings of the dawn arc of the main emission. These events are relatively rare, but they account for some of the brightest aurorae ever observed at ... [more ▼]

Auroral dawn storms at Jupiter are spectacular brightenings of the dawn arc of the main emission. These events are relatively rare, but they account for some of the brightest aurorae ever observed at Jupiter. An event with a total power emitted by the UV aurora in excess of 8.5 TW was even observed by Hisaki and the Hubble Space Telescope on May 21st 2016, during Juno’s approach of Jupiter. On February 7th 2018 (perijove 11, or PJ11), Juno’s ultraviolet imaging spectrograph, called Juno-UVS, observed the development of such a dawn storm, right before Juno flew right through the magnetic field line connected to this feature. The storm started around 13:15 UT as a limited enhancement of the main emission around midnight before slowly migrating and expanding on the dusk flank. As the brightness increased, the arc began to thicken and fork into two separate arcs. Simultaneously, the signatures of methane absorption of the UV light progressively intensified, indicative of a precipitation of increasingly energetic particles. Then, around 18:15 UT, Juno entered the field lines feeding the dawn storm. The remote auroral observations thus provide extremely valuable context information for the in-situ radio waves, particle and magnetic field observations gathered at this time. [less ▲]

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See detailRecurrent magnetic dipolarization process at Saturn: Cassini measurements
Yao, Zhonghua ULiege

Conference (2018, November 09)

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See detailThe polar region of Jupiter’s aurora : barcode noise, conjugate flares and more...
Bonfond, Bertrand ULiege; Grodent, Denis ULiege; Gladstone, Randy et al

Conference (2018, July 11)

Juno’s unprecedented polar orbits around Jupiter allow for unique observations of the polar aurorae and related phenomena. Here we make use of Juno-UVS, the UV imaging spectrograph operating in the 60-200 ... [more ▼]

Juno’s unprecedented polar orbits around Jupiter allow for unique observations of the polar aurorae and related phenomena. Here we make use of Juno-UVS, the UV imaging spectrograph operating in the 60-200 nm range, to explore the polar physics in two very different ways. In the first part of this presentation, we will analyze the rapid variations of the background noise caused by >10MeV electrons penetrating the instrument. In UV images, this rapidly varying signal takes the form of a barcode-like pattern. We will discuss the mapping, the altitude and the characteristic timescale of the “barcode events” in order to constrain the mechanisms giving rise to them. In the second part, we will compare simultaneous observations of the aurorae from the two hemispheres. One dataset comes from Juno-UVS while the other comes from the Hubble Space Telescope STIS instrument. We will show that most auroral features in one hemisphere have a clear counterpart in the other one. Among other examples, we will show evidence of conjugate flares in the active region of the two hemispheres. However, other strong brightness enhancements only show up in one hemisphere, without any echo in the other one. [less ▲]

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See detailAuroral storm and polar arcs at Saturn
Palmaerts, Benjamin ULiege; Radioti, Aikaterini ULiege; Grodent, Denis ULiege et al

Conference (2018, July 11)

On 15 September 2017 the Cassini spacecraft plunged into Saturn's atmosphere after 13 years of successful exploration of the Saturnian system. The day before, the Ultraviolet Imaging Spectrograph (UVIS ... [more ▼]

On 15 September 2017 the Cassini spacecraft plunged into Saturn's atmosphere after 13 years of successful exploration of the Saturnian system. The day before, the Ultraviolet Imaging Spectrograph (UVIS) on board Cassini observed Saturn's northern aurora for about 14h. In this final UVIS sequence, several auroral structures appear, revealing processes occurring simultaneously in Saturn's magnetosphere. A poleward expansion and a brightening of the main emission dawn arc, a phenomenon known as an auroral storm, suggests that an intense flux closure process took place in the magnetotail through magnetic reconnection. This magnetotail reconnection and the associated field dipolarization generated signatures in the auroral, magnetic field, and plasma wave data. The enhanced magnetotail reconnection is likely caused by a compression of the magnetosphere induced by the arrival at Saturn of an interplanetary coronal mass ejection. In addition to the auroral storm, a polar arc observed on the duskside was tracked for the first time from the start of its growth phase until its quasi disappearance, providing evidence of its formation process. This polar arc is a proxy for the location of reconnection sites on the dayside magnetosphere and for the orientation of the interplanetary magnetic field. Finally, the atypical observation of one of the most polar auroral arcs ever reported at Saturn supports the scenario of an interplanetary shock arriving at Saturn at the end of the Cassini mission. In that respect, the ultimate UVIS auroral sequence allowed us to capture dynamical aspects of Saturn’s magnetosphere not frequently or even never observed in the past. [less ▲]

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See detailElectron Dynamics in Magnetosheath Mirror‐Mode Structures
Yao, S. T.; Shi, Q. Q.; Liu, J et al

in Journal of Geophysical Research: Space Physics (2018), 123(7), 5561-5570

Detailed reference viewed: 21 (6 ULiège)
See detailExploring Jupiter's Aurorae with the Chandra and XMM-Newton X-ray Observatories
Dunn, W.; Ray, L.; Kraft, R. et al

in 42nd COSPAR Scientific Assembly (2018, July)

Jupiter's polar X-ray aurora is dominated by a bright dynamic hot spot that is produced by precipitating 10 MeV ions [Gladstone et al. 2002; Elsner et al. 2005; Branduardi-Raymont et al. 2007]. These ... [more ▼]

Jupiter's polar X-ray aurora is dominated by a bright dynamic hot spot that is produced by precipitating 10 MeV ions [Gladstone et al. 2002; Elsner et al. 2005; Branduardi-Raymont et al. 2007]. These highly energetic emissions exhibit pulsations over timescales of 10s of minutes and change morphology, intensity and precipitating particle populations from observation to observation and pole to pole [e.g. Dunn et al. 2017]. Surrounding the soft X-ray emission there is an oval of hard X-ray bremsstrahlung from precipitating electrons. The acceleration process/es that allow Jupiter to produce these high-energy X-ray emissions remain poorly understood, but vary with solar wind conditions [Dunn et al. 2016; Kimura et al. 2016] and the soft X-ray emissions are expected to relate to processes on the boundary between Jupiter's magnetosphere and the solar wind.We present a decade of remote X-ray observations of Jupiter from 2007 to 2017 using the Earth-orbiting X-ray telescopes Chandra and XMM-Newton. We compare these high spatial and spectral resolution X-ray data with in-situ measurements of the solar wind and the Jovian magnetosphere conducted by NASA's New Horizons and Juno spacecraft. Analysing X-ray spectrograms and X-ray auroral videos we probe time-varying accelerations, precipitating particle populations and auroral morphologies and further connect these with their solar wind and in-situ drivers. Finally, we compare X-ray observations with UV observations to enrich multi-waveband connections and deepen our understanding of how Jupiter generates its highly energetic polar auroral precipitations. [less ▲]

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See detailJupiter’s X-ray Aurora Spectra 2016-2017
Dunn, W. R.; Branduardi-Raymont, G.; Ray, L. W. et al

Conference (2018, July)

Poleward of Jupiter’s main auroral emission, there are diverse dynamic multi-waveband aurorae. The most energetic photons observed from this region are X-rays. Most of these X-rays are produced when high ... [more ▼]

Poleward of Jupiter’s main auroral emission, there are diverse dynamic multi-waveband aurorae. The most energetic photons observed from this region are X-rays. Most of these X-rays are produced when high-energy (~10s MeV) ions collide with Jupiter’s atmosphere [Gladstone et al. 2002; Elsner et al. 2005; Branduardi-Raymont et al. 2007; 2008]. These X-ray emissions typically pulse and change morphology, intensity and precipitating particle populations from observation to observation and pole to pole [Kimura et al. 2016; Dunn et al. 2016; 2017; Jackman et al., in review]. The acceleration process/es that allow Jupiter to produce X-rays remain to be confirmed, but probably involve a combination of outer magnetosphere processes and local acceleration at the pole [Cravens et al. 2003; Bunce et al. 2004; Clark et al. 2017; Paranicas et al. 2018]. We present an overview of ~100 hours of XMM-Newton observations of Jupiter from 2016-17 and focus on a 40-hour continuous observation from July 10-12th 2017, during Juno PJ 7. At this time, we observe significant changes in the X-ray aurora from Jupiter rotation to rotation. Amongst these changes, we observe time-varying auroral pulsation rates , which change from a non-regular interval to regular 10-13-min (40-45-min) Northern (Southern) auroral pulses. We also observe time-varying accelerations, with a transient possible sulphur XV line suggesting that the ions may sometimes precipitate with energies in excess of 64 MeV [Kharchenko et al. 2008]. Alongside a range of auroral sulphur and oxygen lines that have previously been observed [Elsner et al. 2005; Branduardi-Raymont et al. 2007; Dunn et al. 2016], we also find spectral lines that are not catalogued as oxygen or sulphur lines, but are at known wavelengths for carbon and/or nitrogen and magnesium, suggesting that the species and abundances of the precipitating ion populations may change with time and/or space. We finish by trying to place these results in the context of other wavebands and their possible physical drivers. [less ▲]

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See detailSaturn’s auroral processes: insights from the Cassini Grand Finale
Badman, S. V.; Bader, A.; Kinrade, J. et al

Conference (2018, July)

Saturn’s auroral emissions display a variety of features reflecting different regions of the magnetosphere. The ‘main’ aurora is usually dominated by a dawn arc mapping to outer, closed field lines. It ... [more ▼]

Saturn’s auroral emissions display a variety of features reflecting different regions of the magnetosphere. The ‘main’ aurora is usually dominated by a dawn arc mapping to outer, closed field lines. It can be complemented by arcs and spots, sometimes pulsating, at high latitudes, likely occurring on field lines open to the solar wind. Diffuse patches or arcs are also detected at lower latitudes corresponding to particles precipitating from the inner regions. The dawn arc itself has a highly variable intensity and structure, modulated by rotating features and storm-like expansions. We review Saturn’s auroral features and the driving mechanisms in light of the measurements made during the high latitude, low altitude Grand Finale orbits. We focus on the intensity and position variability observed on small spatial scales and how the underlying mechanisms can contribute to the global magnetospheric dynamics. [less ▲]

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See detailCo-Rotating Magnetic Reconnection Site in Saturn's Magnetosphere
Yao, Zhonghua ULiege; Coates, A.; Ray, L. et al

Poster (2018, June)

Using measurements from the Cassini spacecraft in Saturn’s magnetosphere, we propose a 3D physical picture of co-rotating reconnection site, which can only be driven by an internally generated source. Our ... [more ▼]

Using measurements from the Cassini spacecraft in Saturn’s magnetosphere, we propose a 3D physical picture of co-rotating reconnection site, which can only be driven by an internally generated source. Our results demonstrate that the co-rotating magnetic reconnection can drive an expansion of the current sheet in Saturn’s magnetosphere, and consequently produce Fermi acceleration of electrons. This reconnection site lasted for longer than one Saturn’s rotation period. The long-lasting and co-rotating natures of magnetic reconnection site at Saturn suggest fundamentally different roles of magnetic reconnection in driving magnetospheric dynamics (e.g., the auroral precipitation) from the Earth. Our co-rotating reconnection picture could also potentially shed light on the fast rotating magnetized plasma environments in the solar system and beyond. [less ▲]

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See detailJupiter's aurora observed with HST during Juno orbits 3 to 7
Grodent, Denis ULiege; Bonfond, Bertrand ULiege; Yao, Zhonghua ULiege et al

in Journal of Geophysical Research. Space Physics (2018), 123

A large set of observations of Jupiter’s ultraviolet aurora was collected with the Hubble Space Telescope concurrently with the NASA-Juno mission, during an 8-month period, from 30 November 2016 to 18 ... [more ▼]

A large set of observations of Jupiter’s ultraviolet aurora was collected with the Hubble Space Telescope concurrently with the NASA-Juno mission, during an 8-month period, from 30 November 2016 to 18 July 2017. These Hubble observations cover Juno orbits 3 to 7 during which Juno in situ and remote sensing instruments, as well as other observatories, obtained a wealth of unprecedented information on Jupiter’s magnetosphere and the connection with its auroral ionosphere. Jupiter’s ultraviolet aurora is known to vary rapidly, with timescales ranging from seconds to one Jovian rotation. The main objective of the present study is to provide a simplified description of the global ultraviolet auroral morphology that can be used for comparison with other quantities, such as those obtained with Juno. This represents an entirely new approach from which logical connections between different morphologies may be inferred. For that purpose, we define three auroral subregions in which we evaluate the auroral emitted power as a function of time. In parallel, we define six auroral morphology families that allow us to quantify the variations of the spatial distribution of the auroral emission. These variations are associated with changes in the state of the Jovian magnetosphere, possibly influenced by Io and the Io plasma torus and by the conditions prevailing in the upstream interplanetary medium. This study shows that the auroral morphology evolved differently during the five ~2-week periods bracketing the times of Juno perijove (PJ03 to PJ07), suggesting that during these periods, the Jovian magnetosphere adopted various states. [less ▲]

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See detailMMS observations of electron scale magnetic peak
Yao, S. T.; Shi, Q. Q.; Guo, R. L. et al

in Geophysical Research Letters (2018)

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See detailRecurrent magnetic dipolarization at Saturn: revealed by Cassini
Yao, Zhonghua ULiege; Radioti, Aikaterini ULiege; Grodent, Denis ULiege et al

in Journal of Geophysical Research: Space Physics (2018), 123(10), 8502-8517

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See detailChina’s roadmap for planetary exploration
Wei, Yong; Yao, Zhonghua ULiege; Wan, Weixing

in Nature Astronomy (2018), 2(5), 346

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See detailElectron Dynamics in Magnetosheath Mirror-Mode Structures
Yao, S. T.; Shi, Q. Q.; Liu, J et al

in Journal of Geophysical Research: Space Physics (2018), 123(7), 5561--5570

Detailed reference viewed: 27 (5 ULiège)