2,056 research outputs found
The plasma environment at geosynchronous orbit
A two-fold objective is considered: (1) to present a picture of the magnetosphere about geosynchronous orbit to the nonspecialist, and (2) to introduce a preliminary model. Particle anisotropies from ATS 6 are included. Omnidirectional electron fluxes are also considered
The 3 DLE instrument on ATS-5
The performance and operation of the DLE plasma electron counter on board the ATS 5 are described. Two methods of data presentation, microfilm line plots and spectrograms, are discussed along with plasma dynamics, plasma flow velocity, electrostatic charging, and wave-particle interactions
The First Stray Light Corrected EUV Images of Solar Coronal Holes
Coronal holes are the source regions of the fast solar wind, which fills most
of the solar system volume near the cycle minimum. Removing stray light from
extreme ultraviolet (EUV) images of the Sun's corona is of high astrophysical
importance, as it is required to make meaningful determinations of temperatures
and densities of coronal holes. EUV images tend to be dominated by the
component of the stray light due to the long-range scatter caused by
microroughness of telescope mirror surfaces, and this component has proven very
difficult to measure in pre-flight characterization. In-flight characterization
heretofore has proven elusive due to the fact that the detected image is
simultaneously nonlinear in two unknown functions: the stray light pattern and
the true image which would be seen by an ideal telescope. Using a constrained
blind deconvolution technique that takes advantage of known zeros in the true
image provided by a fortuitous lunar transit, we have removed the stray light
from solar images seen by the EUVI instrument on STEREO-B in all four filter
bands (171, 195, 284, and 304 \AA). Uncertainty measures of the stray light
corrected images, which include the systematic error due to misestimation of
the scatter, are provided. It is shown that in EUVI, stray light contributes up
to 70% of the emission in coronal holes seen on the solar disk, which has
dramatic consequences for diagnostics of temperature and density and therefore
estimates of key plasma parameters such as the plasma \ and ion-electron
collision rates.Comment: Accepted to Astrophysical Journal Letter
Solar Magnetic Tracking. I. Software Comparison and Recommended Practices
Feature tracking and recognition are increasingly common tools for data
analysis, but are typically implemented on an ad-hoc basis by individual
research groups, limiting the usefulness of derived results when selection
effects and algorithmic differences are not controlled. Specific results that
are affected include the solar magnetic turnover time, the distributions of
sizes, strengths, and lifetimes of magnetic features, and the physics of both
small scale flux emergence and the small-scale dynamo. In this paper, we
present the results of a detailed comparison between four tracking codes
applied to a single set of data from SOHO/MDI, describe the interplay between
desired tracking behavior and parameterization of tracking algorithms, and make
recommendations for feature selection and tracking practice in future work.Comment: In press for Astrophys. J. 200
On the Size of Structures in the Solar Corona
Fine-scale structure in the corona appears not to be well resolved by current
imaging instruments. Assuming this to be true offers a simple geometric
explanation for several current puzzles in coronal physics, including: the
apparent uniform cross-section of bright threadlike structures in the corona;
the low EUV contrast (long apparent scale height) between the top and bottom of
active region loops; and the inconsistency between loop densities derived by
spectral and photometric means. Treating coronal loops as a mixture of diffuse
background and very dense, unresolved filamentary structures address these
problems with a combination of high plasma density within the structures, which
greatly increases the emissivity of the structures, and geometric effects that
attenuate the apparent brightness of the feature at low altitudes. It also
suggests a possible explanation for both the surprisingly high contrast of EUV
coronal loops against the coronal background, and the uniform ``typical''
height of the bright portion of the corona (about 0.3 solar radii) in full-disk
EUV images. Some ramifications of this picture are discussed, including an
estimate (10-100 km) of the fundamental scale of strong heating events in the
corona.Comment: To appear in APJ, June 2007; as accepted Feb 200
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