696 research outputs found
The Structure of the warped Io Plasma Torus constrained by the Io Footprint
Standard models of force balance along Jovian field lines predict the
location of the Io plasma torus to be the centrifugal equator of Jupiter's
magnetosphere, i.e. the position along the magnetic field lines farthest away
from Jupiter's rotational axis. In many models, the centrifugal equator is
assumed to lay on a plane, calculated from a (shifted) dipole magnetic field,
rather than on a warped surface which incorporates Jupiter's higher magnetic
field moments. In this work, we use Hubble Space Telescope observations of the
Io Main Footprint to constrain density, scale height and lateral position of
the Io Plasma Torus. Therefore, we employ the leading angle of the footprints
to calculate expected travel times of Alfven waves and carry out an inversion
of the observations. For the magnetic field we use the JRM33 magnetic field
model. The inversion results show peak densities between 1830 and 2032
particles per cubic centimenter and scale heights between 0.92 and 0.97 Jupiter
radii consistent with current literature values. Using a warped multipole
centrifugal equator instead of a planar dipole increases the quality of the fit
by about twenty-five percent. We additionally develop two tests to confirm that
the multipole centrifugal equator from the JRM33 model fits explains the
applied data set better than the dipole centrifugal equator. The quadropole
moments alter Io's relative position to the torus, which changes the plasma
density around Io by up to twenty percent
Magnetism in the Brown Dwarf Regime
A suite of discoveries in the last two decades demonstrate that we are now at
a point where incorporating magnetic behavior is key for advancing our ability
to characterize substellar and planetary systems. The next decade heralds the
exciting maturation of the now-burgeoning field of brown dwarf magnetism, and
investing now in brown dwarf magnetism will provide a key platform for
exploring exoplanetary magnetism and habitability beyond the solar system. We
anticipate significant discoveries including: the nature of substellar and
planetary magnetic dynamos, the characterization of exo-aurora physics and
brown dwarf magnetospheric environments, and the role of satellites in
manifestations of substellar magnetic activity. These efforts will require
significant new observational capabilities at radio and near infrared
wavelengths, dedicated long-term monitoring programs, and committed support for
the theoretical modeling efforts underpinning the physical processes of the
magnetic phenomenaComment: Decadal 2020 science white pape
Aurora on Ganymede
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98774/1/jgra50122.pd
Ganymede MHD Model: Magnetospheric Context for Juno's PJ34 Flyby
On June 7th, 2021 the Juno spacecraft visited Ganymede and provided the first
in situ observations since Galileo's last flyby in 2000. The measurements
obtained along a one-dimensional trajectory can be brought into global context
with the help of three-dimensional magnetospheric models. Here we apply the
magnetohydrodynamic model of Duling et al. (2014) to conditions during the Juno
flyby. In addition to the global distribution of plasma variables we provide
mapping of Juno's position along magnetic field lines, Juno's distance from
closed field lines and detailed information about the magnetic field's
topology. We find that Juno did not enter the closed field line region and that
the boundary between open and closed field lines on the surface matches the
poleward edges of the observed auroral ovals. To estimate the sensitivity of
the model results, we carry out a parameter study with different upstream
plasma conditions and other model parameters
An entropy stable nodal discontinuous Galerkin method for the resistive MHD equations. Part I: Theory and Numerical Verification
The first paper of this series presents a discretely entropy stable discontinuous Galerkin (DG) method for the resistive magnetohydrodynamics (MHD) equations on three-dimensional curvilinear unstructured hexahedral meshes. Compared to other fluid dynamics systems such as the shallow water equations or the compressible Navier-Stokes equations, the resistive MHD equations need special considerations because of the divergence-free constraint on the magnetic field. For instance, it is well known that for the symmetrization of the ideal MHD system as well as the continuous entropy analysis a non-conservative term proportional to the divergence of the magnetic field, typically referred to as the Powell term, must be included. As a consequence, the mimicry of the continuous entropy analysis in the discrete sense demands a suitable DG approximation of the non-conservative terms in addition to the ideal MHD terms.
This paper focuses on the resistive MHD equations: Our first contribution is a proof that the resistive terms are symmetric and positive-definite when formulated in entropy space as gradients of the entropy variables, which enables us to show that the entropy inequality holds for the resistive MHD equations. This continuous analysis is the key for our DG discretization and guides the path for the construction of an approximation that discretely mimics the entropy inequality, typically termed entropy stability. Our second contribution is a detailed derivation and analysis of the discretization on three-dimensional curvilinear meshes. The discrete analysis relies on the summation-by-parts property, which is satisfied by the DG spectral element method (DGSEM) with Legendre-Gauss-Lobatto (LGL) nodes. Although the divergence- free constraint is included in the non-conservative terms, the resulting method has no particular treatment of the magnetic field divergence errors, which might pollute the solution quality. Our final contribution is the extension of the standard resistive MHD equations and our DG approximation with a divergence cleaning mechanism that is based on a generalized Lagrange multiplier (GLM).
As a conclusion to the first part of this series, we provide detailed numerical validations of our DGSEM method that underline our theoretical derivations. In addition, we show a numerical example where the entropy stable DGSEM demonstrates increased robustness compared to the standard DGSEM
Probing Ganymede's atmosphere with HST Ly images in transit of Jupiter
We report results from far-ultraviolet observations by the Hubble Space
Telescope of Jupiter's largest moon Ganymede transiting across the planet's
dayside hemisphere. {Within} a targeted campaign on 9 September 2021 two
exposures were taken during one transit passage to probe for attenuation of
Jupiter's hydrogen Lyman- dayglow above the moon limb. The background
dayglow is slightly attenuated over an extended region around Ganymede, with
stronger attenuation in the second exposure when Ganymede was near the planet's
center. In the first exposure when the moon was closer to Jupiter's limb, the
effects from the Ganymede corona are hardly detectable, likely because the
Jovian Lyman- dayglow is spectrally broader and less intense at this
viewing geometry. The obtained vertical H column densities of around
~cm are consistent with previous results.
Constraining angular variability around Ganymede's disk, we derive an upper
limit on a local HO column density of ~cm, such
as could arise from outgassing plumes in regions near the observed moon limb
- …