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Hara H.,Japan National Astronomical Observatory | Watanabe T.,Japan National Astronomical Observatory | Harra L.K.,UCL Mullard Space Science Laboratory | Leonard Culhane J.,UCL Mullard Space Science Laboratory | Young P.R.,George Mason University
Astrophysical Journal | Year: 2011

Based on scanning spectroscopic observations with the Hinode EUV imaging spectrometer, we have found a loop-top hot source, a fast jet nearby, and an inflow structure flowing to the hot source that appeared in the impulsive phase of a long-duration flare at the disk center on 2007 May 19. The hot source observed in Fe XXIII and Fe XXIV emission lines has the electron temperature of 12MK and density of 1 × 1010cm-3. It shows excess line broadening, which exceeds the thermal Doppler width by ∼100km s -1, with a weak redshift of ∼30km s-1. We have also observed a blueshifted faint jet whose Doppler velocity exceeds 200km s -1 with an electron temperature of 9MK. Coronal plasmas with electron temperature of 1.2MK and density of 2.5 × 109cm-3 that flow into the loop-top region with a Doppler velocity of 20km s -1 have been identified in the Fe XII observation. They disappeared near the hot source, possibly by being heated to the hotter faint jet temperature. From the geometrical relationships of these phenomena, we conclude that they provide evidence for magnetic reconnection that occurs near the loop-top region. The estimated reconnection rate is 0.05-0.1, which supports the Petschek-type magnetic reconnection. Further supporting evidence for the presence of the slow-mode and fast-mode MHD shocks in the reconnection geometry is given based on the observed quantities. © 2011. The American Astronomical Society. All rights reserved.

News Article | March 22, 2016

It is the first time that Jupiter's X-ray aurora has been studied when a giant storm from the Sun has arrived at the planet. The dramatic findings complement NASA's Juno mission this summer which aims to understand the relationship between the two biggest structures in the solar system—the region of space controlled by Jupiter's magnetic field (i.e. its magnetosphere) and that controlled by the solar wind. "There's a constant power struggle between the solar wind and Jupiter's magnetosphere. We want to understand this interaction and what effect it has on the planet. By studying how the aurora changes, we can discover more about the region of space controlled by Jupiter's magnetic field, and if or how this is influenced by the Sun. Understanding this relationship is important for the countless magnetic objects across the galaxy, including exoplanets, brown dwarfs and neutron stars," explained lead author and PhD student at UCL Mullard Space Science Laboratory, William Dunn. The Sun constantly ejects streams of particles into space in the solar wind. When giant storms erupt, the winds become much stronger and compress Jupiter's magnetosphere, shifting its boundary with the solar wind two million kilometres through space. The study found that this interaction at the boundary triggers the high energy X-rays in Jupiter's Northern Lights, which cover an area bigger than the surface of the Earth. Published today in the Journal of Geophysical Research - Space Physics a publication of the American Geophysical Union, the discovery comes as NASA's Juno spacecraft nears Jupiter for the start of its mission this summer. Launched in 2011, Juno aims to unlock the secrets of Jupiter's origin, helping us to understand how the solar system, including Earth, formed. As part of the mission, Juno will investigate Jupiter's relationship with the Sun and the solar wind by studying its magnetic field, magnetosphere and aurora. The UCL team hope to find out how the X-rays form by collecting complementary data using the European Space Agency's X-ray space observatory, XMM-Newton, and NASA's Chandra X-ray observatory. "Comparing new findings from Jupiter with what is already known for Earth will help explain how space weather is driven by the solar wind interacting with Earth's magnetosphere. New insights into how Jupiter's atmosphere is influenced by the Sun will help us characterise the atmospheres of exoplanets, giving us clues about whether a planet is likely to support life as we know it," said study supervisor, Professor Graziella Branduardi-Raymont, UCL Mullard Space Science Laboratory. The impact of solar storms on Jupiter's aurora was tracked by monitoring the X-rays emitted during two 11 hour observations in October 2011 when an interplanetary coronal mass ejection was predicted to reach the planet from the Sun. The scientists used the data collected to build a spherical image to pinpoint the source of the X-ray activity and identify areas to investigate further at different time points. William Dunn added, "In 2000, one of the most surprising findings was a bright 'hot spot' of X-rays in the aurora which rotated with the planet. It pulsed with bursts of X-rays every 45 minutes, like a planetary lighthouse. When the solar storm arrived in 2011, we saw that the hot spot pulsed more rapidly, brightening every 26 minutes. We're not sure what causes this increase in speed but, because it quickens during the storm, we think the pulsations are also connected to the solar wind, as well as the bright new aurora." Another study out today, led by Tomoki Kimura from the Japan Aerospace Exploration Agency (JAXA) and co-authored by the UCL researchers, reports that the X-ray aurora responds to quieter 'gusts' of solar wind, deepening this connection between Jupiter and the solar wind. The UCL-led study also involved researchers from NASA Marshall Space Flight Center, Boston University, Observatoire de Paris, MIT, Southwest Research Institute (SwRI), University of Southampton, University of Leicester, Japan Aerospace Exploration Agency (JAXA) and University of Michigan. It was kindly funded by the Science and Technology Facilities Council (STFC), NASA, the Natural and Environmental Research Council (NERC) and the Japan Society for the Promotion of Science (JSPS). Explore further: Explosions of Jupiter's aurora linked to extraordinary planet-moon interaction More information: William R. Dunn et al. The Impact of an ICME on the Jovian X-ray Aurora, Journal of Geophysical Research: Space Physics (2016). DOI: 10.1002/2015JA021888

Harra L.K.,UCL Mullard Space Science Laboratory | Sterling A.C.,NASA | Sterling A.C.,Japan Aerospace Exploration Agency | Gomory P.,Slovak Academy of Sciences | Veronig A.,University of Graz
Astrophysical Journal Letters | Year: 2011

We observed a coronal wave (EIT wave) on 2011 February 16, using EUV imaging data from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) and EUV spectral data from the Hinode/EUV Imaging Spectrometer (EIS). The wave accompanied an M1.6 flare that produced a surge and a coronal mass ejection (CME). EIS data of the wave show a prominent redshifted signature indicating line-of-sight velocities of 20kms-1 or greater. Following the main redshifted wave front, there is a low-velocity period (and perhaps slightly blueshifted), followed by a second redshift somewhat weaker than the first; this progression may be due to oscillations of the EUV atmosphere set in motion by the initial wave front, although alternative explanations may be possible. Along the direction of the EIS slit the wave front's velocity was 500kms -1, consistent with its apparent propagation velocity projected against the solar disk as measured in the AIA images, and the second redshifted feature had propagation velocities between 200 and 500kms-1. These findings are consistent with the observed wave being generated by the outgoing CME, as in the scenario for the classic Moreton wave. This type of detailed spectral study of coronal waves has hitherto been a challenge, but is now possible due to the availability of concurrent AIA and EIS data. © 2011. The American Astronomical Society. All rights reserved..

News Article | March 23, 2016

Researchers have found that Jupiter's 'Northern Lights' triggered by the Sun's solar storms are hundreds of times more intense than Earth's aurora borealis. The solar storms produced a new X-ray aurora that is eight times brighter than usual. It's the first time researchers analyzed the phenomenon when the Sun's giant storm arrived on the giant planet. The research was led by the University College London (UCL) and used NASA's Chandra X-Ray Observatory. The findings matched the space agency's Juno mission wherein they aim to analyze the link between two space regions: one controlled by Jupiter's magnetic field and the other by the solar wind. These are our solar system's two biggest structures. Lead author William Dunn said there is a continuous power struggle between Jupiter's magnetosphere and the solar wind. The goal is to analyze the interaction of the two powerful structures and its effect on the giant planet. Study the variations in the auroras can help bring forth more information about the space regions control by Jupiter's magnetosphere and see if it is in any way affected by the Sun. "Understanding this relationship is important for the countless magnetic objects across the galaxy, including exoplanets, brown dwarfs and neutron stars," added Dunn, who is a Ph.D. student at UCL Mullard Space Science Laboratory. The Sun is constantly emitting streams of particles into space through the solar wind. Whenever giant storms take place, the solar winds become more intense and compress the giant planet's magnetosphere. The phenomenon shifts the magnetosphere's boundary 1.2 million miles through space. The two structures' contact at the border creates the high-energy X-rays in the giant planet's aurora. The more intense Northern Lights can then cover an area bigger than the Earth's surface. The observations enabled the researchers to create 3D images of the X-ray phenomenon. The findings can locate Jupiter's magnetic field locations for additional studies. The research was published in the Journal of Geophysical Research - Space Physics on March 22. Graziella Branduardi-Raymont, a UCL researcher who was also part of the study, said that new information on how Jupiter's atmosphere is affected by the Sun can help characterize exoplanets' atmosphere. It can also provide clues if a planet is capable of supporting life.

Harra L.K.,UCL Mullard Space Science Laboratory | Abramenko V.I.,Big Bear Solar Observatory
Astrophysical Journal | Year: 2012

We analyzed Solar Dynamics Observatory line-of-sight magnetograms for a decaying NOAA active region (AR) 11451 along with co-temporal Extreme-Ultraviolet Imaging Spectrometer (EIS) data from the Hinode spacecraft. The photosphere was studied via time variations of the turbulent magnetic diffusivity coefficient, η(t), and the magnetic power spectrum index, α, through analysis of magnetogram data from the Helioseismic and Magnetic Imager (HMI). These measure the intensity of the random motions of magnetic elements and the state of turbulence of the magnetic field, respectively. The time changes of the non-thermal energy release in the corona was explored via histogram analysis of the non-thermal velocity, v nt, in order to highlight the largest values at each time, which may indicate an increase in energy release in the corona. We used the 10% upper range of the histogram of v nt (which we called V upp nt) of the coronal spectral line of Fe XII 195 Å. A 2day time interval was analyzed from HMI data, along with the EIS data for the same field of view. Our main findings are the following. (1) The magnetic turbulent diffusion coefficient, η(t), precedes the upper range of the v nt with the time lag of approximately 2 hr and the cross-correlation coefficient of 0.76. (2) The power-law index, α, of the magnetic power spectrum precedes V upp nt with a time lag of approximately 3 hr and the cross-correlation coefficient of 0.5. The data show that the magnetic flux dispersal in the photosphere is relevant to non-thermal energy release dynamics in the above corona. The results are consistent with the nanoflare mechanism of the coronal heating, due to the time lags being consistent with the process of heating and cooling the loops heated by nanoflares. © 2012. The American Astronomical Society. All rights reserved.

Chen F.,Nanjing University | Ding M.D.,Nanjing University | Chen P.F.,Nanjing University | Harra L.K.,UCL Mullard Space Science Laboratory
Astrophysical Journal | Year: 2011

We report a spectroscopic analysis of an EUV Imaging Telescope (EIT) wave event that occurred in active region 11081 on 2010 June 12 and was associated with an M2.0 class flare. The wave propagated nearly circularly. The southeastern part of the wave front passed over an upflow region near a magnetic bipole. Using EUV Imaging Spectrometer raster observations for this region, we studied the properties of plasma dynamics in the wave front, as well as the interaction between the wave and the upflow region. We found a weak blueshift for the Fe XII λ195.12 and Fe XIII λ202.04 lines in the wave front. The local velocity along the solar surface, which is deduced from the line-of-sight velocity in the wave front and the projection effect, is much lower than the typical propagation speed of the wave. A more interesting finding is that the upflow and non-thermal velocities in the upflow region are suddenly diminished after the transit of the wave front. This implies a significant change of magnetic field orientation when the wave passed. As the lines in the upflow region are redirected, the velocity along the line of sight is diminished as a result. We suggest that this scenario is more in accordance with what was proposed in the field-line stretching model of EIT waves. © 2011. The American Astronomical Society. All rights reserved.

Chen P.F.,Nanjing University | Harra L.K.,UCL Mullard Space Science Laboratory | Fang C.,Nanjing University
Astrophysical Journal | Year: 2014

The dynamics of a filament channel are observed with imaging and spectroscopic telescopes before and during the filament eruption on 2011 January 29. The extreme ultraviolet (EUV) spectral observations reveal that there are no EUV counterparts of the Hα counter-streamings in the filament channel, implying that the ubiquitous Hα counter-streamings found by previous research are mainly due to longitudinal oscillations of filament threads, which are not in phase between each other. However, there exist larger-scale patchy counter-streamings in EUV along the filament channel from one polarity to the other, implying that there is another component of unidirectional flow (in the range of ±10 km s-1) inside each filament thread in addition to the implied longitudinal oscillation. Our results suggest that the flow direction of the larger-scale patchy counter-streaming plasma in the EUV is related to the intensity of the plage or active network, with the upflows being located at brighter areas of the plage and downflows at the weaker areas. We propose a new method to determine the chirality of an erupting filament on the basis of the skewness of the conjugate filament drainage sites. This method suggests that the right-skewed drainage corresponds to sinistral chirality, whereas the left-skewed drainage corresponds to dextral chirality. © 2014. The American Astronomical Society. All rights reserved.

Prise A.J.,UCL Mullard Space Science Laboratory | Harra L.K.,UCL Mullard Space Science Laboratory | Matthews S.A.,UCL Mullard Space Science Laboratory | Long D.M.,UCL Mullard Space Science Laboratory | Aylward A.D.,University College London
Solar Physics | Year: 2014

Multi-spacecraft observations are used to study the in-situ effects of a large coronal mass ejection (CME) erupting from the farside of the Sun on 3 November 2011, with particular emphasis on the associated solar energetic particle (SEP) event. At that time both Solar Terrestrial Relations Observatory (STEREO) spacecraft were located more than 90 degrees from Earth and could observe the CME eruption directly, with the CME visible on-disk from STEREO-B and off the limb from STEREO-A. Signatures of pressure variations in the corona such as deflected streamers were seen, indicating the presence of a coronal shock associated with this CME eruption. The evolution of the CME and an associated extreme-ultraviolet (EUV) wave were studied using EUV and coronagraph images. It was found that the lateral expansion of the CME low in the corona closely tracked the propagation of the EUV wave, with measured velocities of 240±19 km s-1 and 221±15 km s-1 for the CME and wave, respectively. Solar energetic particles were observed to arrive first at STEREO-A, followed by electrons at the Wind spacecraft at L1, then STEREO-B, and finally protons arrived simultaneously at Wind and STEREO-B. By carrying out a velocity-dispersion analysis on the particles arriving at each location, it was found that energetic particles arriving at STEREO-A were released first and that the release of particles arriving at STEREO-B was delayed by about 50 minutes. Analysis of the expansion of the CME to a wider longitude range indicates that this delay is a result of the time taken for the CME edge to reach the footpoints of the magnetic-field lines connected to STEREO-B. The CME expansion is not seen to reach the magnetic footpoint of Wind at the time of solar-particle release for the particles detected here, suggesting that these particles may not be associated with this CME. © 2013 Springer Science+Business Media Dordrecht.

Harra L.K.,UCL Mullard Space Science Laboratory | Matthews S.A.,UCL Mullard Space Science Laboratory | Long D.M.,UCL Mullard Space Science Laboratory | Doschek G.A.,U.S. Navy | De Pontieu B.,Lockheed Martin
Astrophysical Journal | Year: 2014

The first spectroscopic observations of cool Mg II loops above the solar limb observed by NASA's Interface Region Imaging Spectrograph (IRIS) are presented. During the observation period, IRIS is pointed off-limb, allowing the observation of high-lying loops, which reach over 70 Mm in height. Low-lying cool loops were observed by the IRIS slit-jaw camera for the entire four-hour observing window. There is no evidence of a central reversal in the line profiles, and the Mg II h/k ratio is approximately two. The Mg II spectral lines show evidence of complex dynamics in the loops with Doppler velocities reaching ±40 km s-1. The complex motions seen indicate the presence of multiple threads in the loops and separate blobs. Toward the end of the observing period, a filament eruption occurs that forms the core of a coronal mass ejection. As the filament erupts, it impacts these high-lying loops, temporarily impeding these complex flows, most likely due to compression. This causes the plasma motions in the loops to become blueshifted and then redshifted. The plasma motions are seen before the loops themselves start to oscillate as they reach equilibrium following the impact. The ratio of the Mg h/k lines also increases following the impact of the filament. © 2014. The American Astronomical Society. All rights reserved.

Madjarska M.S.,Armagh Observatory | Madjarska M.S.,UCL Mullard Space Science Laboratory | Huang Z.,Armagh Observatory | Doyle J.G.,Armagh Observatory | Subramanian S.,Armagh Observatory
Astronomy and Astrophysics | Year: 2012

Context. We report on the plasma properties of small-scale transient events identified in the quiet Sun, coronal holes and their boundaries. Aims. We aim at deriving the physical characteristics of events that were identified as small-scale transient brightenings in XRT images. Methods. We used spectroscopic co-observations from SUMER/SoHO and EIS/Hinode combined with high-cadence imaging data from XRT/Hinode. We measured Doppler shifts using single and multiple Gaussian fits of the transition region and coronal lines as well as electron densities and temperatures. We combined co-temporal imaging and spectroscopy to separate brightening expansions from plasma flows. Results. The transient brightening events in coronal holes and their boundaries were found to be very dynamical, producing high-density outflows at high speeds. Most of these events represent X-ray jets from pre-existing or newly emerging coronal bright points at X-ray temperatures. The average electron density of the jets is log 10 N e 8.76 cm -3 while in the flaring site it is log 10 N e 9.51 cm -3. The jet temperatures reach a maximum of 2.5 MK but in the majority of the cases the temperatures do not exceed 1.6 MK. The footpoints of jets have maximum temperatures of 2.5 MK, though in a single event scanned a minute after the flaring the measured temperature was 12 MK. The jets are produced by multiple microflaring in the transition region and corona. Chromospheric emission was only detected in their footpoints and was only associated with downflows. The Doppler shift measurements in the quiet Sun transient brightenings confirmed that these events do not produce jet-like phenomena. The plasma flows in these phenomena remain trapped in closed loops. Conclusions. We can conclude that the dynamic day-by-day and even hour-by-hour small-scale evolution of coronal hole boundaries reported in Paper I is indeed related to coronal bright points. The XRT observations reported in Paper II revealed that these changes are associated with the dynamic evolution of coronal bright points producing multiple jets during their lifetime until their full disappearance. We demonstrate here through spectroscopic EIS and SUMER co-observations combined with high-cadence imaging information that the co-existence of open and closed magnetic fields results in multiple energy depositions, which propel high-density plasma along open magnetic field lines. We conclude from the physical characteristics obtained in this study that X-ray jets are important candidates for the source of the slow solar wind. This, however, does not exclude the possibility that these jets are also the microstreams observed in the fast solar wind, as recently suggested. © ESO, 2012.

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