95 research outputs found
Sun-as-a-Star Observation of Flares in Lyman {\alpha} by the PROBA2/LYRA radiometer
There are very few reports of flare signatures in the solar irradiance at H i
Lyman {\alpha} at 121.5 nm, i.e. the strongest line of the solar spectrum. The
LYRA radiometer onboard PROBA2 has observed several flares for which
unambiguous signatures have been found in its Lyman-{\alpha} channel. Here we
present a brief overview of these observations followed by a detailed study of
one of them, the M2 flare that occurred on 8 February 2010. For this flare, the
flux in the LYRA Lyman-{\alpha} channel increased by 0.6%, which represents
about twice the energy radiated in the GOES soft X-ray channel and is
comparable with the energy radiated in the He ii line at 30.4 nm. The
Lyman-{\alpha} emission represents only a minor part of the total radiated
energy of this flare, for which a white-light continuum was detected.
Additionally, we found that the Lyman-{\alpha} flare profile follows the
gradual phase but peaks before other wavelengths. This M2 flare was very
localized and has a very brief impulsive phase, but more statistics are needed
to determine if these factors influence the presence of a Lyman-{\alpha} flare
signal strong enough to appear in the solar irradiance.Comment: in press for Solar Physic
The LYRA Instrument Onboard PROBA2: Description and In-Flight Performance
The Large Yield Radiometer (LYRA) is an XUV-EUV-MUV (soft X-ray to
mid-ultraviolet) solar radiometer onboard the European Space Agency PROBA2
mission that was launched in November 2009. LYRA acquires solar irradiance
measurements at a high cadence (nominally 20 Hz) in four broad spectral
channels, from soft X-ray to MUV, that have been chosen for their relevance to
solar physics, space weather and aeronomy. In this article, we briefly review
the design of the instrument, give an overview of the data products distributed
through the instrument website, and describe the way that data are calibrated.
We also briefly present a summary of the main fields of research currently
under investigation by the LYRA consortium
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.Comment: Topical Issue: Flares, CMEs and SEPs and their space weather impacts;
20 pages; 7 figures; Presented during 13th European Space Weather Week, 201
Simple Magnetic Flux Balance as an Indicator of Neon VIII Doppler Velocity Partitioning in an Equatorial Coronal Hole
We present a novel investigation into the relationship between simple
estimates of magnetic flux balance and the Ne VIII Doppler velocity
partitioning of a large equatorial coronal hole observed by the Solar
Ultraviolet Measurements of Emitted Radiation spectrometer (SUMER) on the Solar
and Heliospheric Observatory (SOHO) in November 1999. We demonstrate that a
considerable fraction of the large scale Doppler velocity pattern in the
coronal hole can be qualitatively described by simple measures of the local
magnetic field conditions, i.e., the relative unbalance of magnetic polarities
and the radial distance required to balance local flux concentrations with
those of opposite polarity.Comment: To appear ApJL (June
In-flight performance of the solar UV radiometer LYRA/PROBA-2
LYRA is a solar radiometer, part of the PROBA-2 micro-satellite payload (Fig. 1). The PROBA-2 [1] 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. PROBA-2 is a small satellite developed under an ESA General Support Technology Program (GSTP) contract to perform an in-flight demonstration of new space technologies and support a scientific mission for a set of selected instruments [2]. PROBA-2 host 17 technological demonstrators and 4 scientific instruments. The mission is tracked by the ESA Redu Mission Operation Center. One of the four scientific instruments is LYRA that monitors the solar irradiance at a high cadence (> 20 Hz) 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 [3]. LYRA benefits from wide bandgap detectors based on diamond. It is the first space assessment of these revolutionary UV detectors for astrophysics. Diamond sensors make the instruments radiation-hard and solar-blind (insensitive to the strong solar visible light) and, therefore, visible light blocking filters become superfluous. To correlate the data of this new detector technology, silicon detectors with well known characteristics are also embarked. Due to the strict allocated mass and power budget (5 kg, 5W), and poor priority to the payload needs on such platform, an optimization and a robustness of the instrument was necessary. The first switch-on occured on 16 November 2009. Since then the instrument performances have been monitored and analyzed during the commissioning period. This paper presents the first-light and preliminary performance analysis
Detection of Solar Rotational Variability in the LYRA 190 - 222 nm Spectral Band
We analyze the variability of the spectral solar irradiance during the period
from 7 January, 2010 until 20 January, 2010 as measured by the Herzberg channel
(190-222 nm) of the Large Yield RAdiometer (LYRA) onboard PROBA2. In this
period of time observations by the LYRA nominal unit experienced degradation
and the signal produced by the Herzberg channel frequently jumped from one
level to another. Both these factors significantly complicates the analysis. We
present the algorithm which allowed us to extract the solar variability from
the LYRA data and compare the results with SORCE/SOLSTICE measurements and with
modeling based on the Code for the Solar Irradiance (COSI)
Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling
This review paper outlines background information and covers recent advances
made via the analysis of spectra and images of prominence plasma and the
increased sophistication of non-LTE (ie when there is a departure from Local
Thermodynamic Equilibrium) radiative transfer models. We first describe the
spectral inversion techniques that have been used to infer the plasma
parameters important for the general properties of the prominence plasma in
both its cool core and the hotter prominence-corona transition region. We also
review studies devoted to the observation of bulk motions of the prominence
plasma and to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically thick at
certain wavelengths. Therefore, complex non-LTE models become necessary. We
thus present the basics of non-LTE radiative transfer theory and the associated
multi-level radiative transfer problems. The main results of one- and
two-dimensional models of the prominences and their fine-structures are
presented. We then discuss the energy balance in various prominence models.
Finally, we outline the outstanding observational and theoretical questions,
and the directions for future progress in our understanding of solar
prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a
better resolution in the published version. New version reflects minor
changes brought after proof editin
Observations of the Sun at Vacuum-Ultraviolet Wavelengths from Space. Part II: Results and Interpretations
- …