Sunquake with a second bounce, other sunquakes, and emission associated with the X9.3 flare of 6 September 2017. I. Observations

Aims. The 6 September 2017 X9.3 solar flare produced very unique observations of magnetic field transients and a few seismic responses, or sunquakes, detected by the Helioseismic and Magnetic Imager (HMI) instrument aboard Solar Dynamic Observatory (SDO) spacecraft, including the strongest sunquake ever reported. This flare was one of a few flares occurring within a few days or hours in the same active region. Despite numerous reports of the fast variations of magnetic field, and seismic and white light emission, no attempts were made to interpret the flare features using multi-wavelength observations. In this study, we attempt to produce the summary of available observations of the most powerful flare of the 6 September 2017 obtained using instruments with different spatial resolutions (this paper) and to provide possible interpretation of the flaring events, which occurred in the locations of some seismic sources (a companion Paper II). Methods. We employed non-linear force-free field extrapolations followed by magnetohydrodynamic simulations in order to identify the presence of several magnetic flux ropes prior to the initiation of this X9.3 flare. Sunquakes were observed using the directional holography and time–distance diagram detection techniques. The high-resolution method to detect the Hα line kernels in the CRISP instrument at the diffraction level limit was also applied. Results. We explore the available γ-ray (GR), hard X-ray (HXR), Lyman-α, and extreme ultra-violet (EUV) emission for this flare comprising two flaring events observed by space- and ground-based instruments with different spatial resolutions. For each flaring event we detect a few seismic sources, or sunquakes, using Dopplergrams from the HMI/SDO instrument coinciding with the kernels of Hα line emission with strong redshifts and white light sources. The properties of sunquakes were explored simultaneously with the observations of HXR (with KONUS/WIND and the Reuven Ramaty High Energy Solar Spectroscopic Imager payload), EUV (with the Atmospheric Imaging Assembly (AIA/SDO and the EUV Imaging Spectrometer aboard Hinode payload), Hα line emission (with the CRisp Imaging Spectro-Polarimeter (CRISP) in the Swedish Solar Telescope), and white light emission (with HMI/SDO). The locations of sunquake and Hα kernels are associated with the footpoints of magnetic flux ropes formed immediately before the X9.3 flare onset. Conclusions. For the first time we present the detection of the largest sunquake ever recorded with the first and second bounces of acoustic waves generated in the solar interior, the ripples of which appear at a short distance of 5–8 Mm from the initial flare location. Four other sunquakes were also detected, one of which is likely to have occurred 10 min later in the same location as the largest sunquake. Possible parameters of flaring atmospheres in the locations with sunquakes are discussed using available temporal and spatial coverage of hard X-ray, GR, EUV, hydrogen Hα-line, and white light emission in preparation for their use in an interpretation to be given in Paper II

Response of the low ionosphere to X-ray and Lyman-a solar flare emissions

International audience[1] Using soft X-ray measurements from detectors onboard the Geostationary Operational Environmental Satellite (GOES) and simultaneous high-cadence Lyman-a observations from the Large Yield Radiometer (LYRA) onboard the Project for On-Board Autonomy 2 (PROBA2) ESA spacecraft, we study the response of the lower part of the ionosphere, the D region, to seven moderate to medium-size solar flares that occurred in February and March of 2010. The ionospheric disturbances are analyzed by monitoring the resulting sub-ionospheric wave propagation anomalies detected by the South America Very Low Frequency (VLF) Network (SAVNET). We find that the ionospheric disturbances, which are characterized by changes of the VLF wave phase, do not depend on the presence of Lyman-a radiation excesses during the flares. Indeed, Lyman-a excesses associated with flares do not produce measurable phase changes. Our results are in agreement with what is expected in terms of forcing of the lower ionosphere by quiescent Lyman-a emission along the solar activity cycle. Therefore, while phase changes using the VLF technique may be a good indicator of quiescent Lyman-a variations along the solar cycle, they cannot be used to scale explosive Lyman-a emission during flares

Simultaneous Observations of the Chromosphere with TRACE and SUMER

Using mainly the 1600 angstrom continuum channel, and also the 1216 angstrom Lyman-alpha channel (which includes some UV continuum and C IV emission), aboard the TRACE satellite, we observed the complete lifetime of a transient, bright chromospheric loop. Simultaneous observations with the SUMER instrument aboard the SOHO spacecraft revealed interesting material velocities through the Doppler effect existing above the chromospheric loop imaged with TRACE, possibly corresponding to extended non-visible loops, or the base of an X-ray jet.Comment: 14 pages, 10 figures, accepted by Solar Physic

Solar EUV irradiance during solar cycle 24 as observed by PROBA2/LYRA and SDO/EVE

International audienceSolar EUV irradiance affects the upper atmospheres of planets and is a fundamental parameters for space weather. The Large-Yield Radiometer (LYRA) is a radiometer that has monitored the solar irradiance at high cadence and in four pass bands since January 2010. Both the instrument and its spacecraft, PROBA2 (Project for OnBoard Autonomy), have several innovative features for space instrumentation, which makes the data reduction necessary to retrieve the long-term variations of solar irradiance more complex than for a fully optimized solar physics mission. In this presentation, we describe how we compute the long-term time series of the two extreme ultraviolet irradiance channels of LYRA and compare the results with those of SDO/EVE and several proxies

A theoretical network model to analyse neurogenesis and synaptogenesis in the dentate gyrus

Butz M, Lehmann K, Dammasch IE, Teuchert-Noodt G. A theoretical network model to analyse neurogenesis and synaptogenesis in the dentate gyrus. NEURAL NETWORKS. 2006;19(10):1490-1505.We describe a strongly biologically motivated artificial neural network approach to model neurogenesis and synaptic turnover as it naturally occurs for example in the hippocampal dentate gyrus (DG) of the developing and adult mammalian and human brain. The results suggest that cell proliferation (CP) has not only a functional meaning for computational tasks and learning but is also relevant for maintaining homeostatic stability of the neural activity. Moderate rates of CP buffer disturbances in input activity more effectively than networks without or very high CR. Up to a critical mark an increase of CP enhances synaptogenesis which might be beneficial for learning. However, higher rates of CP are rather ineffective as they destabilize the network: high CP rates and a disturbing input activity effect a reduced cell survival. By these results the simulation model sheds light on the recurrent interdependence of structure and function in biological neural networks especially in hippocampal circuits and the interacting morphogenetic effects of neurogenesis and synaptogenesis. (c) 2006 Elsevier Ltd. All rights reserved

IN-FLIGHT PERFORMANCE OF THE SOLAR UV RADIOMETER LYRA / PROBA-2

LYRA is a solar radiometer, part of the PROBA-2 micro-satellite payload. The PROBA-2 mission has been launched on 02 November 2009 with a Rockot launcher to a Sun-synchronous orbit at an altitude of 725 km. Its nominal operation duration is two years with possible extension of 2 years. LYRA monitors the solar irradiance at a high cadence (> 20Hz) in four soft X-Ray to VUV large passbands: the “Lyman-Alpha” channel, the “Herzberg” continuum range, the “Aluminium” and “Zirconium” filter channels. The radiometric calibration is traceable to synchrotron source standards. LYRA benefits from wide bandgap detectors based on diamond. It is the first space assessment of these revolutionary UV detectors for astrophysics.LYR

On-orbit degradation of recent space-based solar instruments and understanding of the degradation processes

International audienceThe space environment is considered hazardous to spacecraft, resulting in materials degradation. Understanding the degradation of space-based instruments is crucial in order to achieve the scientific objectives, which are derived from these instruments. This paper discusses the on-orbit performance degradation of recent spacebased solar instruments. We will focus on the instruments of three space-based missions such as the Project for On-Board Autonomy 2 (PROBA2) spacecraft, the Solar Monitoring Observatory (SOLAR) payload onboard the Columbus science Laboratory of the International Space Station (ISS) and the PICARD spacecraft. Finally, this paper intends to understand the degradation processes of these space-based solar instruments

Solar Activity Monitoring of Flares and CMEs Precursors: the Importance of Lyman-Alpha

International audienceEvents preceding the onset of a are are called 'precursors', and one of the prominent precursors is a newly emerging bipolar region at the surface, which may interact with pre-existing magnetic field in the corona and trigger a flare. Another well-known precursor is the activation, or eruption, of a filament that is composed of relatively cool plasma (around 10000 K), oated in the hot coronal plasma. Both emerging regions and filaments are well observed in Lyman-Alpha and H-Alpha and we expect that their combination might lead to a better identification of the changes at the origin of major flares and CMEs. The objective of the study we present, carried with the LYRA/PROBA-2 instrument (observations of early 2010) and H-Alpha observations (Hida Observatory), is to monitor flares in Lyman-Alpha and to compare sensitivity difference with H-Alpha to develop better precursor indicators on the flaring region. Comparison is also made with classical EUV { X-ray indicators (GOES 1-8 A but also LYRA channels 2- 3, Aluminum 17{80 nm, and 2-4, Zirconium 6{20 nm), showing that Lyman-Alpha flares are equally sensitive and detectable, with the advantage, though, of providing significant precursors. H-Alpha - although 1000 times less intense as a flare than Lyman-Alpha (exemple of C9.9 February 2010 are presented) - is indicative of the precursor elements to study. Many H- Alpha observations sources are available but we preferably use Peru or Hida Observatory data when available since providing velocities (spectroheliograms). This Lyman-Alpha flares and precursors study is pursued with recent observations campaigns with a spare Lyman detector of LYRA. But this interesting possibility to open and watch for flares from a promising region implies, accordingly, to rely on good precursors indications to limit filter's degradation. These observations are pointing the interest for future Lyman-Alpha irradiance measurements coupled, for precursors identification, to solar disk imaging

The detection of ultra-relativistic electrons in low Earth orbit

Aims. To better understand the radiation environment in low Earth orbit (LEO), the analysis of in-situ observations of a variety of particles, at different atmospheric heights, and in a wide range of energies, is needed. Methods. We present an analysis of energetic particles, indirectly detected by the large yield radiometer (LYRA) instrument on board ESA's project for on-board autonomy 2 (PROBA2) satellite as background signal. Combining energetic particle telescope (EPT) observations with LYRA data for an overlapping period of time, we identified these particles as electrons with an energy range of 2 to 8 MeV. Results. The observed events are strongly correlated to geo-magnetic activity and appear even during modest disturbances. They are also well confined geographically within the L = 4–6 McIlwain zone, which makes it possible to identify their source. Conclusions. Although highly energetic particles are commonly perturbing data acquisition of space instruments, we show in this work that ultra-relativistic electrons with energies in the range of 2–8 MeV are detected only at high latitudes, while not present in the South Atlantic Anomaly region