367 research outputs found
Plasma streams in the Hermean dayside magnetosphere: Solar wind injection through the reconnection region
International audienceThe aim of this research is to simulate the interaction of the solar wind with the magnetic field of Mercury and to study the particle fluxes between the magnetosheath and the planet surface. We simulate the magnetosphere structure using the open source MHD code PLUTO in spherical geometry with a multipolar expansion of the Hermean magnetic field (Anderson, B. J. et al, 2012). We perform two simulations with realistic solar wind parameters to study the properties of a plasma stream originated in the reconnection region between the interplanetary and the Hermean magnetic field. The plasma precipitates along the open magnetic field lines to the planet surface showing a fast expansion, rarefaction and cooling. The plasma stream is correlated with a flattening of the magnetic field observed by MESSENGER due to the adjacency of the reconnection region where the solar wind is injected to the inner magnetosphere
Heating of the solar wind with electron and proton effects
We examine the effects of including effects of both protons and electrons on the heating of the fast solar wind through two different approaches. In the first approach, we incorporate the electron temperature in an MHD turbulence transport model for the solar wind. In the second approach, we adopt more empirically based methods by analyzing the measured proton and electron temperatures to calculate the heat deposition rates. Overall, we conclude that incorporating separate proton and electron temperatures and heat conduction effects provides an improved and more complete model of the heating of the solar wind
Modeling the Enceladus plume--plasma interaction
We investigate the chemical interaction between Saturn's corotating plasma
and Enceladus' volcanic plumes. We evolve plasma as it passes through a
prescribed H2O plume using a physical chemistry model adapted for water-group
reactions. The flow field is assumed to be that of a plasma around an
electrically-conducting obstacle centered on Enceladus and aligned with
Saturn's magnetic field, consistent with Cassini magnetometer data. We explore
the effects on the physical chemistry due to: (1) a small population of hot
electrons; (2) a plasma flow decelerated in response to the pickup of fresh
ions; (3) the source rate of neutral H2O. The model confirms that charge
exchange dominates the local chemistry and that H3O+ dominates the water-group
composition downstream of the Enceladus plumes. We also find that the amount of
fresh pickup ions depends heavily on both the neutral source strength and on
the presence of a persistent population of hot electrons.Comment: 10 pages, 1 table, 2 figure
Density fluctuations measured by ISEE 1-2 in the Earth's magnetosheath and the resultant scattering of radio waves
The Near-Sun Streamer Belt Solar Wind: Turbulence and Solar Wind Acceleration
The fourth orbit of Parker Solar Probe (PSP) reached heliocentric distances
down to 27.9 Rs, allowing solar wind turbulence and acceleration mechanisms to
be studied in situ closer to the Sun than previously possible. The turbulence
properties were found to be significantly different in the inbound and outbound
portions of PSP's fourth solar encounter, likely due to the proximity to the
heliospheric current sheet (HCS) in the outbound period. Near the HCS, in the
streamer belt wind, the turbulence was found to have lower amplitudes, higher
magnetic compressibility, a steeper magnetic field spectrum (with spectral
index close to -5/3 rather than -3/2), a lower Alfv\'enicity, and a "1/f" break
at much lower frequencies. These are also features of slow wind at 1 au,
suggesting the near-Sun streamer belt wind to be the prototypical slow solar
wind. The transition in properties occurs at a predicted angular distance of
~4{\deg} from the HCS, suggesting ~8{\deg} as the full-width of the streamer
belt wind at these distances. While the majority of the Alfv\'enic turbulence
energy fluxes measured by PSP are consistent with those required for
reflection-driven turbulence models of solar wind acceleration, the fluxes in
the streamer belt are significantly lower than the model predictions,
suggesting that additional mechanisms are necessary to explain the acceleration
of the streamer belt solar wind
A Sensitivity Study of the Enceladus Torus
We have developed a homogeneous model of physical chemistry to investigate
the neutral-dominated, water-based Enceladus torus. Electrons are treated as
the summation of two isotropic Maxwellian distributionsa thermal component
and a hot component. The effects of electron impact, electron recombination,
charge exchange, and photochemistry are included. The mass source is neutral
HO, and a rigidly-corotating magnetosphere introduces energy via pickup of
freshly-ionized neutrals. A small fraction of energy is also input by Coulomb
collisions with a small population ( 1%) of supra-thermal electrons. Mass
and energy are lost due to radial diffusion, escaping fast neutrals produced by
charge exchange and recombination, and a small amount of radiative cooling. We
explore a constrained parameter space spanned by water source rate, ion radial
diffusion, hot-electron temperature, and hot-electron density. The key findings
are: (1) radial transport must take longer than 12 days; (2) water is input at
a rate of 100--180 kg s; (3) hot electrons have energies between 100 and
250 eV; (4) neutrals dominate ions by a ratio of 40:1 and continue to dominate
even when thermal electrons have temperatures as high as 5 eV; (5)
hot electrons do not exceed 1% of the total electron population within the
torus; (6) if hot electrons alone drive the observed longitudinal variation in
thermal electron density, then they also drive a significant variation in ion
composition.Comment: 9 pages text, 3 tables, 9 figure
Total Electron Temperature Derived from Quasi-Thermal Noise Spectroscopy In the Pristine Solar Wind: Parker Solar Probe Observations
The Quasi-thermal noise (QTN) technique is a reliable tool to yield accurate
measurements of the electron parameters in the solar wind. We apply this method
on Parker Solar Probe (PSP) observations to derive the total electron
temperature () from the linear fit of the high-frequency part of the QTN
spectra acquired by the RFS/FIELDS instrument, and present a combination of
12-day period of observations around each perihelion from Encounter One (E01)
to Ten (E10) (with E08 not included) with the heliocentric distance varying
from about 13 to 60 solar radii (). We find that the total electron
temperature decreases with the distance as , which is much
slower than adiabatic. The extrapolated based on PSP observations is
consistent with the exospheric solar wind model prediction at 10
, Helios observations at 0.3 AU and Wind observations at 1 AU.
Also, , extrapolated back to 10 , is almost the same as the
strahl electron temperature (measured by SPAN-E) which is considered to
be closely related to or even almost equal to the coronal electron temperature.
Furthermore, the radial profiles in the slower solar wind (or flux tube
with larger mass flux) are steeper than those in the faster solar wind (or flux
tube with smaller mass flux). More pronounced anticorrelated - is
observed when the solar wind is slower and closer to the Sun.Comment: 10 pages, 7 figures, and Astronomy & Astrophysics Accepte
Cotton breeding in Australia : meeting the challenges of the 21st century
The Commonwealth Scientific and Industrial Research Organisation (CSIRO) cotton breeding program is the sole breeding effort for cotton in Australia, developing high performing cultivars for the local industry which is worth∼AU$3 billion per annum. The program is supported by Cotton Breeding Australia, a Joint Venture between CSIRO and the program’s commercial partner, Cotton Seed Distributors Ltd. (CSD). While the Australian industry is the focus, CSIRO cultivars have global impact in North America, South America, and Europe. The program is unique compared with many other public and commercial breeding programs because it focuses on diverse and integrated research with commercial outcomes. It represents the full research pipeline, supporting extensive long-term fundamental molecular research; native and genetically modified (GM) trait development; germplasm enhancement focused on yield and fiber quality improvements; integration of third-party GM traits; all culminating in the release of new commercial cultivars. This review presents evidence of past breeding successes and outlines current breeding efforts, in the areas of yield and fiber quality improvement, as well as the development of germplasm that is resistant to pests, diseases and abiotic stressors. The success of the program is based on the development of superior germplasm largely through field phenotyping, together with strong commercial partnerships with CSD and Bayer CropScience. These relationships assist in having a shared focus and ensuring commercial impact is maintained, while also providing access to markets, traits, and technology. The historical successes, current foci and future requirements of the CSIRO cotton breeding program have been used to develop a framework designed to augment our breeding system for the future. This will focus on utilizing emerging technologies from the genome to phenome, as well as a panomics approach with data management and integration to develop, test and incorporate new technologies into a breeding program. In addition to streamlining the breeding pipeline for increased genetic gain, this technology will increase the speed of trait and marker identification for use in genome editing, genomic selection and molecular assisted breeding, ultimately producing novel germplasm that will meet the coming challenges of the 21st Century
Density fluctuations measured by ISEE 1-2 in the Earth's magnetosheath and the resultant scattering of radio waves
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