284 research outputs found
Modelling of EIS spectrum drift from instrumental temperatures
An empirical model has been developed to reproduce the drift of the spectrum
recorded by EIS on board Hinode using instrumental temperatures and relative
motion of the spacecraft. The EIS spectrum shows an artificial drift in
wavelength dimension in sync with the revolution of the spacecraft, which is
caused by temperature variations inside the spectrometer. The drift amounts to
70 km s in Doppler velocity and introduces difficulties in velocity
measurements. An artificial neural network is incorporated to establish a
relationship between the instrumental temperatures and the spectral drift. This
empirical model reproduces observed spectrum shift with an rms error of 4.4 km
s. This procedure is robust and applicable to any spectrum obtained with
EIS, regardless of of the observing field. In addition, spectral curvatures and
spatial offset in the North - South direction are determined to compensate for
instrumental effects.Comment: 16 pages, 12 Figures, accepted for publication in Solar Physics.
Added description of neural networ
Alternative data reduction for precise and accurate isotope ratio determination via LA-MC-ICP-MS
An alternative approach for the evaluation of isotope ratio data using LA-MC-ICP-MS will be presented. In contrast to previously applied methods it is based on the simultaneous
responses of all analyte isotopes of interest and the relevant interferences without performing a conventional background correction.
Significant improvements in precision and accuracy can
be achieved when applying this new method and will be
discussed based on the results of two first methodical
applications: a) radiogenic and stable Sr isotopes in carbonates b) stable chlorine isotopes of pyrohydrolytic extracts.
In carbonates an external reproducibility of the 87Sr/86Sr
ratios of about 19 ppm (RSD) was achieved, an improvement
of about a factor of 5. For recent and sub-recent marine
carbonates a mean radiogenic strontium isotope ratio 87Sr/86Sr of 0.709170 ± 0.000007 (2SE) was determined, which agrees well with the value of 0.7091741 ± 0.0000024 (2SE) reported for modern sea water [1].
Stable chlorine isotope ratios were determined ablating
pyrohydrolytic extracts with a reproducibility of about 0.05‰ (RSD). For basaltic reference material JB1a and JB2 chlorine isotope ratios were determined relative to SMOC (standard mean ocean chlorinity) δ37ClJB-1a = (-0.99 ± 0.06) ‰ and δ37ClJB-2 = (-0.60 ± 0.03) ‰ (2SE), respectively, in accordance with published data [2].
The described strategies for data reduction are considered
to be generally applicable for all isotope ratio measurements using LA-MC-ICP-MS.
[1] McArthur, Rio, Massari, Castradori, Bailey, Thirlwall &
Houghton (2006) Palaeogeo. Palaeoclim. Palaeoeco. 242,
126, doi: 10.1016/j.palaeo.2006.06.004 [2] Fietzke,. Frische, Hansteen & Eisenhauer (2008) J. Anal. At. Spectrom. 2008, doi:10.1039/B718597A
A Tale Of Two Spicules: The Impact of Spicules on the Magnetic Chromosphere
We use high-resolution observations of the Sun in Ca II H 3968 A from the
Solar Optical Telescope on Hinode to show that there are at least two types of
spicules that dominate the structure of the magnetic solar chromosphere. Both
types are tied to the relentless magnetoconvective driving in the photosphere,
but have very different dynamic properties. ``Type-I'' spicules are driven by
shock waves that form when global oscillations and convective flows leak into
the upper atmosphere along magnetic field lines on 3-7 minute timescales.
``Type-II'' spicules are much more dynamic: they form rapidly (in ~10s), are
very thin (<200km wide), have lifetimes of 10-150s (at any one height) and seem
to be rapidly heated to (at least) transition region temperatures, sending
material through the chromosphere at speeds of order 50-150 km/s. The
properties of Type II spicules suggest a formation process that is a
consequence of magnetic reconnection, typically in the vicinity of magnetic
flux concentrations in plage and network. Both types of spicules are observed
to carry Alfven waves with significant amplitudes of order 20 km/s.Comment: 8 pages, 5 figures, accepted for Hinode special issue of PAS
An alternative data acquisition and evaluation strategy for improved isotope ratio precision using LA-MC-ICP-MS applied to stable and radiogenic strontium isotopes in carbonates
Strontium isotopes in various marine carbonates were determined using an “AXIOM” MC-ICP-MS in combination with a NewWave UP193 laser ablation unit. Using a modified measurement and data reduction strategy, an external reproducibility of 87Sr/86Sr ratios in carbonates of about 19 ppm (RSD) was achieved. For recent and sub-recent marine carbonates a mean radiogenic strontium isotope ratio 87Sr/86Sr of 0.709170 ± 0.000007 (2SE) was determined, which agrees well with the value of 0.7091741 ± 0.0000024 (2SE) reported for modern sea water (J. M. McArthur, D. Rio, F. Massari, D. Castrodi, T. R. Bailey, M. Thirlwall and S. Houghton, Palaeogeogr. Palaeoclimatol. Palaeoeco., 2006, 242(126), 2006). Compared to published laser-based methods, an improved accuracy and precision was achieved by applying a new data reduction protocol using the simultaneous responses of all isotopes measured. The latter is considered as a new principal approach for isotope ratio evaluation using LA-MC-ICP-MS. A major advantage of the presented method is the direct determination of the stable strontium isotope fractionation. Providing reproducible sample ablation, introduction into the plasma and stable plasma condition, this method excludes the efforts of a quantitative strontium recovery after ion chromatographic separation to avoid additional fractionation of the sample strontium due to chemical pre-treatment/separation (ion chromatography and solution preparation), and is therefore, together with the quicker sample preparation and spatially resolved analysis, advantageous when compared to published solution–nebulization bracketing-standard MC-ICP-MS methods for stable strontium isotope determination
Bombs and flares at the surface and lower atmosphere of the Sun
This research was supported by the Research Council of Norway and by the European Research Council under the European Union's Seventh Framework Programme (FP7/2007–2013)/ERC Grant agreement no. 291058.A spectacular manifestation of solar activity is the appearance of transient brightenings in the far wings of the Hα line, known as Ellerman bombs (EBs). Recent observations obtained by the Interface Region Imaging Spectrograph have revealed another type of plasma "bombs" (UV bursts) with high temperatures of perhaps up to 8 × 104 K within the cooler lower solar atmosphere. Realistic numerical modeling showing such events is needed to explain their nature. Here, we report on 3D radiative magnetohydrodynamic simulations of magnetic flux emergence in the solar atmosphere. We find that ubiquitous reconnection between emerging bipolar magnetic fields can trigger EBs in the photosphere, UV bursts in the mid/low chromosphere and small (nano-/micro-) flares (106 K) in the upper chromosphere. These results provide new insights into the emergence and build up of the coronal magnetic field and the dynamics and heating of the solar surface and lower atmosphere.Publisher PDFPeer reviewe
Intermittent reconnection and plasmoids in UV bursts in the low solar atmosphere
Magnetic reconnection is thought to drive a wide variety of dynamic phenomena
in the solar atmosphere. Yet the detailed physical mechanisms driving
reconnection are difficult to discern in the remote sensing observations that
are used to study the solar atmosphere. In this paper we exploit the
high-resolution instruments Interface Region Imaging Spectrograph (IRIS) and
the new CHROMIS Fabry-Perot instrument at the Swedish 1-m Solar Telescope (SST)
to identify the intermittency of magnetic reconnection and its association with
the formation of plasmoids in so-called UV bursts in the low solar atmosphere.
The Si IV 1403A UV burst spectra from the transition region show evidence of
highly broadened line profiles with often non-Gaussian and triangular shapes,
in addition to signatures of bidirectional flows. Such profiles had previously
been linked, in idealized numerical simulations, to magnetic reconnection
driven by the plasmoid instability. Simultaneous CHROMIS images in the
chromospheric Ca II K 3934A line now provide compelling evidence for the
presence of plasmoids, by revealing highly dynamic and rapidly moving
brightenings that are smaller than 0.2 arcsec and that evolve on timescales of
order seconds. Our interpretation of the observations is supported by detailed
comparisons with synthetic observables from advanced numerical simulations of
magnetic reconnection and associated plasmoids in the chromosphere. Our results
highlight how subarcsecond imaging spectroscopy sensitive to a wide range of
temperatures combined with advanced numerical simulations that are realistic
enough to compare with observations can directly reveal the small-scale
physical processes that drive the wide range of phenomena in the solar
atmosphere.Comment: Accepted for publication in Astrophysical Journal Letters. Movies are
available at http://folk.uio.no/rouppe/plasmoids_chromis
An Interface Region Imaging Spectrograph first view on Solar Spicules
Solar spicules have eluded modelers and observers for decades. Since the
discovery of the more energetic type II, spicules have become a heated topic
but their contribution to the energy balance of the low solar atmosphere
remains unknown. Here we give a first glimpse of what quiet Sun spicules look
like when observed with NASA's recently launched Interface Region Imaging
Spectrograph (IRIS). Using IRIS spectra and filtergrams that sample the
chromosphere and transition region we compare the properties and evolution of
spicules as observed in a coordinated campaign with Hinode and the Atmospheric
Imaging Assembly. Our IRIS observations allow us to follow the thermal
evolution of type II spicules and finally confirm that the fading of Ca II H
spicules appears to be caused by rapid heating to higher temperatures. The IRIS
spicules do not fade but continue evolving, reaching higher and falling back
down after 500-800 s. Ca II H type II spicules are thus the initial stages of
violent and hotter events that mostly remain invisible in Ca II H filtergrams.
These events have very different properties from type I spicules, which show
lower velocities and no fading from chromospheric passbands. The IRIS spectra
of spicules show the same signature as their proposed disk counterparts,
reinforcing earlier work. Spectroheliograms from spectral rasters also confirm
that quiet Sun spicules originate in bushes from the magnetic network. Our
results suggest that type II spicules are indeed the site of vigorous heating
(to at least transition region temperatures) along extensive parts of the
upward moving spicular plasma.Comment: 6 pages, 4 figures, accepted for publication in ApJ Letters. For
associated movies, see http://folk.uio.no/tiago/iris_spic
Vectorial Control of Magnetization by Light
Coherent light-matter interactions have recently extended their applications
to the ultrafast control of magnetization in solids. An important but
unrealized technique is the manipulation of magnetization vector motion to make
it follow an arbitrarily designed multi-dimensional trajectory. Furthermore,
for its realization, the phase and amplitude of degenerate modes need to be
steered independently. A promising method is to employ Raman-type nonlinear
optical processes induced by femtosecond laser pulses, where magnetic
oscillations are induced impulsively with a controlled initial phase and an
azimuthal angle that follows well defined selection rules determined by the
materials' symmetries. Here, we emphasize the fact that temporal variation of
the polarization angle of the laser pulses enables us to distinguish between
the two degenerate modes. A full manipulation of two-dimensional magnetic
oscillations is demonstrated in antiferromagnetic NiO by employing a pair of
polarization-twisted optical pulses. These results have lead to a new concept
of vectorial control of magnetization by light
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