85 research outputs found
OXYGEN ABUNDANCE AND ENERGY DEPOSITION IN THE SLOW CORONAL WIND
Observations of the extended corona obtained with the Ultraviolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO) during the solar minimum years 1996 and 1997 have been analyzed to derive the oxygen abundance in the outer corona. A comparison of the absolute coronal abundance, measured in the coronal regions surrounding the quiescent solar minimum streamers, to the heliospheric values confirms that these regions are the dominant sources of the slow solar wind. However, the inferred coronal abundances are consistent with the heliospheric values only in case the ion velocity distribution is anisotropic and enhanced across the coronal magnetic field. Thus this analysis also leads to the conclusion that energy is deposited in the slow coronal wind at least up to 2.7 R☉ and that the efficiency of energy deposition is likely to be related to the local coronal magnetic topology
Modeling of Joint Parker Solar Probe - Metis/Solar Orbiter Observations
We present a first theoretical modeling of joint Parker Solar Probe (PSP) -
Metis/Solar Orbiter (SolO) quadrature observations Telloni et al 2022c. The
combined observations describe the evolution of a slow solar wind plasma parcel
from the extended solar corona ( R) to the very inner
heliosphere (23.2 R). The Metis/SolO instrument remotely measures the
solar wind speed finding a range from kms, and PSP measures the
solar wind plasma in situ, observing a radial speed of 219.34 kms. We
find theoretically and observationally that the solar wind speed accelerates
rapidly within 3.3 -- 4 R, and then increases more gradually with
distance. Similarly, we find that the theoretical solar wind density is
consistent with the remotely and in situ observed solar wind density. The
normalized cross-helicity and normalized residual energy observed by PSP are
0.96 and -0.07, respectively, indicating that the slow solar wind is very
Alfv\'enic. The theoretical NI/slab results are very similar to PSP
measurements, which is a consequence of the highly magnetic field-aligned
radial flow ensuring that PSP can measure slab fluctuations and not 2D.
Finally, we calculate the theoretical 2D and slab turbulence pressure, finding
that the theoretical slab pressure is very similar to that observed by PSP.Comment: 12 pages, 5 figure
LISA Pathfinder test-mass charging during galactic cosmic-ray flux short-term variations
none5sìMetal free-floating test masses aboard the future interferometers devoted to gravitational wave detection in space are charged by galactic and solar cosmic rays with energies > 100 MeV/n. This process represents one of the main sources of noise in the lowest frequency band (< 10(-3) Hz) of these experiments. We study here the charging of the LISA Pathfinder (LISA-PF) gold-platinum test masses due to galactic cosmic-ray (GCR) protons and helium nuclei with the Fluka Monte Carlo toolkit. Projections of the energy spectra of GCRs during the LISA-PF operations in 2015 are considered. This work was carried out on the basis of the solar activity level and solar polarity epoch expected for LISA-PF. The effects of GCR short-term variations are evaluated here for the first time. Classical Forbush decreases, GCR variations induced by the Sun rotation, and fluctuations in the LISA-PF frequency bandwidth are discussed.Article Number: 035001openGrimani, Catia; Fabi, M.; Lobo, A.; Mateos, I.; Telloni, D.Grimani, Catia; Fabi, M.; Lobo, A.; Mateos, I.; Telloni, D
Radial Evolution of Spectral Characteristics of Magnetic Field Fluctuations at Proton Scales
This paper addresses the investigation of the character and the radial evolution of magnetic fluctuations within the dissipation range, right after the high-frequency spectral break, employing observations by Messenger and Wind of the same fast wind stream during a radial alignment. The same event has already been considered in literature to show, for the first time, that the high-frequency break separating the fluid from the kinetic regime moves to lower frequency as the wind expands. The present work aims to analyze the nature of the high-frequency magnetic fluctuations beyond the spectral break and show that their character is compatible with left-hand, outward-propagating, ion cyclotron waves and right-hand kinetic Alfv\acute{e}n waves. It is also shown that the low-frequency limit of these fluctuations follows the radial evolution of the spectral break, which also reflects in the behavior of their intermittency character. Finally, the total power and the compressive character of these two wave populations are analyzed and compared as a function of the heliocentric distance, leading us to conclude that the overall picture is in favor of a radial decrease
Predicting the COSIE-C Signal from the Outer Corona up to 3 Solar Radii
We present estimates of the signal to be expected in quiescent solar
conditions, as would be obtained with the COronal Spectrographic Imager in the
EUV in its coronagraphic mode (COSIE-C). COSIE-C has been proposed to routinely
observe the relatively unexplored outer corona, where we know that many
fundamental processes affecting both the lower corona and the solar wind are
taking place. The COSIE-C spectral band, 186--205 A, is well-known as it has
been observed with Hinode EIS. We present Hinode EIS observations that we
obtained in 2007 out to 1.5 Rsun, to show that this spectral band in quiescent
streamers is dominated by Fe XII and Fe XI and that the ionization temperature
is nearly constant. To estimate the COSIE-C signal in the 1.5--3.1 Rsun region
we use a model based on CHIANTI atomic data and SoHO UVCS observations in the
Si XII and Mg X coronal lines of two quiescent 1996 streamers. We reproduce the
observed EUV radiances with a simple density model, photospheric abundances,
and a constant temperature of 1.4 MK. We show that other theoretical or
semi-empirical models fail to reproduce the observations. We find that the
coronal COSIE-C signal at 3 Rsun should be about 5 counts/s per 3.1" pixel in
quiescent streamers. This is unprecedented and opens up a significant discovery
space. We also briefly discuss stray light and the visibility of other solar
features. In particular, we present UVCS observations of an active region
streamer, indicating increased signal compared to the quiet Sun cases.Comment: Accepted for publication in Ap
Recurrent galactic cosmic-ray flux modulation in L1 and geomagnetic activity during the declining phase of the solar cycle 24
Galactic cosmic-ray (GCR) flux short-term variations (1 month) in the
inner heliosphere are mainly associated with the passage of high-speed solar
wind streams (HSS) and interplanetary (IP) counterparts of coronal mass
ejections (ICMEs). Data gathered with a particle detector flown on board the
ESA LISA Pathfinder (LPF) spacecraft, during the declining part of the solar
cycle 24 (February 2016 - July 2017) around the Lagrange point L1, have allowed
to study the characteristics of recurrent cosmic-ray flux modulations above 70
MeV n. %These modulations are observed when the solar wind speed is
400 km s and/or the IP magnetic field intensity 10 nT. It is shown
that the amplitude and evolution of individual modulations depend in a unique
way on both IP plasma parameters and particle flux intensity before HSS and
ICMEs transit. By comparing the LPF data with those gathered contemporaneously
with the magnetic spectrometer experiment AMS-02 on board the International
Space Station and with those of Earth polar neutron monitors, the GCR flux
modulation was studied at different energies during recurrent short-term
variations. It is also aimed to set the near real-time particle observation
requirements to disentangle the role of long and short-term variations of the
GCR flux to evaluate the performance of high-sensitivity instruments in space
such as the future interferometers for gravitational wave detection. Finally,
the association between recurrent GCR flux variation observations in L1 and
weak to moderate geomagnetic activity in 2016-2017 is discussed. Short-term
recurrent GCR flux variations are good proxies of recurrent geomagnetic
activity when the B component of the IP magnetic field is directed
northern
Study of Galactic Cosmic-Ray Flux Modulation by Interplanetary Plasma Structures for the Evaluation of Space Instrument Performance and Space Weather Science Investigations
The role of high-energy particles in limiting the performance of on-board instruments was studied for the European Space Agency (ESA) Laser Interferometer Space Antenna (LISA) Pathfinder (LPF) and ESA/National Astronautics and Space Administration Solar Orbiter missions. Particle detectors (PD) placed on board the LPF spacecraft allowed for testing the reliability of pre-launch predictions of galactic cosmic-ray (GCR) energy spectra and for studying the modulation of proton and helium overall flux above 70 MeV n − 1 on a day-by-day basis. GCR flux variations up to approximately 15% in less than a month were observed with LPF orbiting around the Lagrange point L1 between 2016 and 2017. These variations appeared barely detected or undetected in neutron monitors. In this work the LPF data and contemporaneous observations carried out with the magnetic spectrometer AMS-02 experiment are considered to show the effects of GCR flux short-term variations with respect to monthly averaged measurements. Moreover, it is shown that subsequent large-scale interplanetary structures cause a continuous modulation of GCR fluxes. As a result, small Forbush decreases cannot be considered good proxies for the transit of interplanetary coronal mass ejections and for geomagnetic storm forecasting
PERSISTENT AND SELF-SIMILAR LARGE-SCALE DENSITY FLUCTUATIONS IN THE SOLAR CORONA
Density fluctuations of the low and midlatitude solar corona plasma are analyzed during the recent solar minimum period. Long time series of the intensity of the neutral hydrogen Lyα, 1216 A, line have been observed with the UltraViolet Coronagraph Spectrometer/Solar and Heliospheric Observatory at 1.7 R ☉, in low-latitude streamers and in regions where the slow solar wind is accelerated. Their frequency composition is investigated by using three different techniques, namely the Fourier, the Hurst, and the phase coherence analyses. The Fourier analysis reveals the existence of low-frequency f –α power spectra in the range from ~3 × 10–6 Hz to ~10–4 Hz, corresponding to periods from a few hours to a few days. The coronal density fluctuations are dominated by discontinuities separating structures with a minimum characteristic timescale of about 3 hr and a corresponding spatial scale of about 3 × 104 km. The nonlinear analysis technique based on the structure functions shows that for large timescales the coronal density fluctuations are statistically self-affine and give rise to an average Hurst exponent H = 0.654 ± 0.008. This indicates that the process underlying the variability of the corona and the slow wind at coronal level is a persistent mechanism, generating correlations among the plasma density fluctuations. Finally, the analysis based on the phase coherence index shows a high degree of phase synchronization of the coronal density variations for large timescales, which shows that the solar corona is dominated by phase coherent structures. The results of the analysis suggest a coupling of the variability of the solar corona and the photospheric dynamics induced by the convection at supergranular scale
Efficient kinetic Lattice Boltzmann simulation of three-dimensional Hall-MHD Turbulence
Simulating plasmas in the Hall-MagnetoHydroDynamics (Hall-MHD) regime
represents a valuable {approach for the investigation of} complex non-linear
dynamics developing in astrophysical {frameworks} and {fusion machines}. Taking
into account the Hall electric field is {computationally very challenging as}
it involves {the integration of} an additional term, proportional to \bNabla
\times ((\bNabla\times\mathbf{B})\times \mathbf{B}) in the Faraday's induction
{law}. {The latter feeds back on} the magnetic field at small
scales (between the ion and electron inertial scales), {requiring} very high
resolution{s} in both space and time {in order to properly describe its
dynamics.} The computational {advantage provided by the} kinetic Lattice
Boltzmann (LB) approach is {exploited here to develop a new} code, the
\textbf{\textsc{F}}ast \textbf{\textsc{L}}attice-Boltzmann
\textbf{\textsc{A}}lgorithm for \textbf{\textsc{M}}hd
\textbf{\textsc{E}}xperiments (\textsc{flame}). The \textsc{flame} code
integrates the plasma dynamics in lattice units coupling two kinetic schemes,
one for the fluid protons (including the Lorentz force), the other to solve the
induction equation describing the evolution of the magnetic field. Here, the
newly developed algorithm is tested against an analytical wave-solution of the
dissipative Hall-MHD equations, pointing out its stability and second-order
convergence, over a wide range of the control parameters. Spectral properties
of the simulated plasma are finally compared with those obtained from numerical
solutions from the well-established pseudo-spectral code \textsc{ghost}.
Furthermore, the LB simulations we present, varying the Hall parameter,
highlightthe transition from the MHD to the Hall-MHD regime, in excellent
agreement with the magnetic field spectra measured in the solar wind
STATISTICS OF DENSITY FLUCTUATIONS DURING THE TRANSITION FROM THE OUTER SOLAR CORONA TO THE INTERPLANETARY SPACE
This paper investigates the evolution of the plasma density fluctuations of the fast and slow solar wind from the solar corona into the interplanetary space. The study is performed by comparing the low-frequency spectra and the phase correlation of the proton density oscillations, measured in the inner heliosphere with the Helios 2 in situ instrumentation, with those due to the large-scale density perturbations observed with UVCS/SOHO in the outer corona. We find that the characteristics of density fluctuations of the fast solar wind are maintained in the transition from the outer corona to the inner heliosphere, thus suggesting a coronal imprint for the heliospheric large-scale 1/f 2 noise spectrum. In contrast, a quick dynamical evolution is observed in the slow wind, which, starting from large-scale fluctuations with strong phase correlations in the outer corona, gives rise to a Kolmogorov-like spectrum and an accumulation of density structures at small scales at 0.3 AU. This can be explained in the framework of nearly incompressible turbulence
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