700 research outputs found
The long-term effects of space weather on satellite operations
Integrated lifetime radiation damage may cause spacecraft to become
more susceptible to operational anomalies by changing material
characteristics of electronic components. This study demonstrates and
quantifies the impact of these effects by examining the National Oceanic and
Atmospheric Administration (NOAA) National Geophysical Data Center (NGDC)
satellite anomaly database. Energetic particle data from the Geostationary
Operational Environmental Satellites (GOES) is used to construct the total
lifetime particle exposure a satellite has received at the epoch of an
anomaly. These values are compared to the satellite's chronological age and
the average exposure per year (calculated over two solar cycles.) The results
show that many anomalies occur on satellites that have received a total
lifetime high-energy particle exposure that is disproportionate to their age.
In particular, 10.8% of all events occurred on satellites that received over
two times more 20 to 40 MeV proton lifetime particle exposure than predicted
using an average annual mean. This number inflates to 35.2% for 40 to 80 MeV
protons and 33.7% for ≥2 MeV electrons. Overall, 73.5% of all
anomalies occurred on a spacecraft that had experienced greater than two
times the expected particle exposure for one of the eight particle
populations used in this study. Simplistically, this means that the long term
radiation background exposure matters, and that if the background radiation
is elevated during the satellite's lifetime, the satellite is likely to
experience more anomalies than satellites that have not been exposed to the
elevated environment
A maximum spreading speed for magnetopause reconnection
Past observations and numerical modeling find magnetic reconnection to initiate at a localized region and then spread along a current sheet. The rate of spreading has been proposed to be controlled by a number of mechanisms based on the properties within the boundary. At the Earth's magnetopause the spreading speed is also limited by the speed at which a shocked solar wind front can move along the magnetopause boundary. The speed at which a purely north to south rotational discontinuity propagates through the magnetosheath and contacts the magnetopause is measured here using the BlockâAdaptiveâTree Solar Wind RoeâType Upwind Scheme global magnetohydrodynamics model. The propagation speed along the magnetopause is fastest near the nose of the magnetopause and decreases with distance from the subsolar point. The average propagation speed along the dayside magnetopause is 847 km/s. This is significantly larger than observed rates of reconnection spreading at the magnetopause of 30â40 km/s indicating that, for the observed conditions, the speed of front propagation along the magnetopause does not limit or control the spreading rate of reconnection.Published versio
Outflow in global magnetohydrodynamics as a function of a passive inner boundary source
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106972/1/jgra50946.pd
The ionospheric source of magnetospheric plasma is not a black box input for global models
Including ionospheric outflow in global magnetohydrodynamic models of nearâEarth outer space has become an important step toward understanding the role of this plasma source in the magnetosphere. Of the existing approaches, however, few tie the outflowing particle fluxes to magnetospheric conditions in a selfâconsistent manner. Doing so opens the magnetosphereâionosphere system to nonlinear massâenergy feedback loops, profoundly changing the behavior of the magnetosphereâionosphere system. Based on these new results, it is time for the community eschew treating ionospheric outflow as a simple black box source of magnetospheric plasma.Key PointsIonospheric outflow plays a critical role in the magnetosphereThe magnetosphere affects outflowModelers must account for this twoâway relationshipPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/133592/1/jgra52677_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133592/2/jgra52677.pd
Validation of SWMF magnetic field and plasma
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94788/1/swe345.pd
Bulk sediment parameters (CaCO3, TOC, >63”m) of Sites 1095, 1096, 1101 and coarse fraction analysis of Site 1095 (ODP Leg 178, Western Antarctic Peninsula)
The 2+1 Kepler Problem and Its Quantization
We study a system of two pointlike particles coupled to three dimensional
Einstein gravity. The reduced phase space can be considered as a deformed
version of the phase space of two special-relativistic point particles in the
centre of mass frame. When the system is quantized, we find some possibly
general effects of quantum gravity, such as a minimal distances and a foaminess
of the spacetime at the order of the Planck length. We also obtain a
quantization of geometry, which restricts the possible asymptotic geometries of
the universe.Comment: 59 pages, LaTeX2e, 9 eps figure
Numerical considerations in simulating the global magnetosphere
Magnetohydrodynamic (MHD) models of the global magnetosphere are very
good research tools for investigating the topology and dynamics of the
near-Earth space environment. While these models have obvious
limitations in regions that are not well described by the MHD
equations, they can typically be used (or are used) to investigate the
majority of magnetosphere. Often, a secondary consideration is
overlooked by researchers when utilizing global models â the effects
of solving the MHD equations on a grid, instead of analytically. Any
discretization unavoidably introduces numerical artifacts that affect
the solution to various degrees. This paper investigates some of the
consequences of the numerical schemes and grids that are used to solve
the MHD equations in the global magnetosphere. Specifically, the
University of Michigan's MHD code is used to investigate the role of
grid resolution, numerical schemes, limiters, inner magnetospheric
density boundary conditions, and the artificial lowering of the speed
of light on the strength of the ionospheric cross polar cap potential
and the build up of the ring current in the inner magnetosphere. It
is concluded that even with a very good solver and the highest
affordable grid resolution, the inner magnetosphere is not grid
converged. Artificially reducing the speed of light reduces the
numerical diffusion that helps to achieve better agreement with data.
It is further concluded that many numerical effects work nonlinearly
to complicate the interpretation of the physics within the
magnetosphere, and so simulation results should be scrutinized very
carefully before a physical interpretation of the results is made.
Our conclusions are not limited to the Michigan MHD code, but apply to
all MHD models due to the limitations of computational resources
(2+1)-dimensional Einstein-Kepler problem in the centre-of-mass frame
We formulate and analyze the Hamiltonian dynamics of a pair of massive
spinless point particles in (2+1)-dimensional Einstein gravity by anchoring the
system to a conical infinity, isometric to the infinity generated by a single
massive but possibly spinning particle. The reduced phase space \Gamma_{red}
has dimension four and topology R^3 x S^1. \Gamma_{red} is analogous to the
phase space of a Newtonian two-body system in the centre-of-mass frame, and we
find on \Gamma_{red} a canonical chart that makes this analogue explicit and
reduces to the Newtonian chart in the appropriate limit. Prospects for
quantization are commented on.Comment: 38 pages, REVTeX v3.1 with amsfonts and epsf, 12 eps figures. (v2:
Presentational improvement, references added, typos corrected.
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