530 research outputs found
Observations of large-scale motions of the Sun
Recent observations of large-scale mass motions on the Sun are discussed. The principal large-scale velocity flows are convection, rotation, meridional flow, and torsional and radial oscillations
Coordinated observations in support of the solar maximum mission
The in-orbit repair of the Solar Maximum Mission satellite has provided an opportunity to continue observations of the Sun's outer corona, transition region, and bolometric flux through the decay phase and minimum of the solar cycle. The coordinated observation of the solar photosphere, chromosphere, and low corona from the ground is a necessary companion to understanding the full range of phenomena seen over the solar cycle by the spacecraft instruments. A program of such observations has been undertaken at the Mees Solar Observatory, and has established a broad database for the analysis of the solar atmosphere and interior
H alpha observations of the 12 August 1975 type 3-RS bursts
H alpha filtergram observations of a number of the Type III-RS (reverse slope) bursts that occurred on August 12, 1975 are presented. Solar radio emission was peculiar on that date in that a large number, and proportion, of the usually rare reverse slope bursts were observed. The radio bursts are shown to coincide in time with a homologous set of H alpha flares located at the limbward edge of spot group Mt. Wilson 19598. A model is proposed in which the reverse slope bursts are the downward branches of U bursts, whose upward branches are hidden behind the coronal density enhancement over the spot group
The Nature of Solar Polar Rays
We use time series observations from the SOHO and Yohkoh spacecraft to study
solar polar rays. Contrary to our expectations, we find that the rays are
associated with active regions on the sun and are not features of the polar
coronal holes. They are extended, hot plasma structures formed in the active
regions and projected onto the plane of the sky above the polar coronal holes.
We present new observations and simple projection models that match long-lived
polar ray structures seen in limb synoptic maps. Individual projection patterns
last for at least 5 solar rotations.Comment: 10 pages, 5 PostScript figures. Fig.1 is in color. The paper is also
available at http://www.ifa.hawaii.edu/users/jing/papers.htm
An imaging vector magnetograph for the next solar maximum
Researchers describe the conceptual design of a new imaging vector magnetograph currently being constructed at the University of Hawaii. The instrument combines a modest solar telescope with a rotating quarter-wave plate, an acousto-optical tunable prefilter as a blocker for a servo-controlled Fabry-Perot etalon, CCD cameras, and on-line digital image processing. Its high spatial resolution (1/2 arcsec pixel size) over a large field of view (5 by 5 arcmin) will be sufficient to significantly measure, for the first time, the magnetic energy dissipated in major solar flares. Its millisecond tunability and wide spectral range (5000 to 7000 A) enable nearly simultaneous vector magnetic field measurements in the gas-pressure-dominated photosphere and magnetically-dominated chromosphere, as well as effective co-alignment with Solar-A's X ray images. Researchers expect to have the instrument in operation at Mees Solar Observatory (Haleakala) in early 1991. They have chosen to use tunable filters as wavelength-selection elements in order to emphasize the spatial relationships between magnetic field elements, and to permit construction of a compact, efficient instrument. This means that spectral information must be obtained from sequences of images, which can cause line profile distortions due to effects of atmospheric seeing
Solar Irradiance Variations on Active Region Time Scales
The variations of the total solar irradiance is an important tool for studying the Sun, thanks to the development of very precise sensors such as the ACRIM instrument on board the Solar Maximum Mission. The largest variations of the total irradiance occur on time scales of a few days are caused by solar active regions, especially sunspots. Efforts were made to describe the active region effects on total and spectral irradiance
Mechanical properties of the hollow-wall graphene gyroid lattice
© 2020 The macroscopic elastic modulus and yield strength of solid-wall nickel gyroids and hollow-wall graphene gyroids of cell size 60 nm are deduced from indentation tests on a thin coating of the gyroids, with suitable interpretation by finite element simulations. The solid-wall nickel gyroids are fabricated by the self-assembly of a triblock copolymer, followed by the chemical vapour deposition of a graphene film onto this catalytic template. The nano-indentation response of the gyroid-based coatings was measured using a Berkovich indenter. In order to interpret the indentation response, two sets of finite element simulations were performed: periodic cell calculations in order to deduce the effective macroscopic properties in terms of the relative density and cell wall properties of the lattice, and then indentation simulations of a continuum with the effective properties of the gyroid. Despite the knockdown in modulus and strength of the graphene gyroid lattice due to waviness of the layered cell walls, the structure remains remarkably strong due to nanoscale size effects
Does the Babcock--Leighton Mechanism Operate on the Sun?
The contribution of the Babcock-Leighton mechanism to the generation of the
Sun's poloidal magnetic field is estimated from sunspot data for three solar
cycles. Comparison of the derived quantities with the A-index of the
large-scale magnetic field suggests a positive answer to the question posed in
the title of this paper.Comment: 5 pages, 2 figures, to apper in Astronomy Letter
Solar Flares and Coronal Mass Ejections: A Statistically Determined Flare Flux-CME Mass Correlation
In an effort to examine the relationship between flare flux and corresponding
CME mass, we temporally and spatially correlate all X-ray flares and CMEs in
the LASCO and GOES archives from 1996 to 2006. We cross-reference 6,733 CMEs
having well-measured masses against 12,050 X-ray flares having position
information as determined from their optical counterparts. For a given flare,
we search in time for CMEs which occur 10-80 minutes afterward, and we further
require the flare and CME to occur within +/-45 degrees in position angle on
the solar disk. There are 826 CME/flare pairs which fit these criteria.
Comparing the flare fluxes with CME masses of these paired events, we find CME
mass increases with flare flux, following an approximately log-linear, broken
relationship: in the limit of lower flare fluxes, log(CME mass)~0.68*log(flare
flux), and in the limit of higher flare fluxes, log(CME mass)~0.33*log(flare
flux). We show that this broken power-law, and in particular the flatter slope
at higher flare fluxes, may be due to an observational bias against CMEs
associated with the most energetic flares: halo CMEs. Correcting for this bias
yields a single power-law relationship of the form log(CME mass)~0.70*log(flare
flux). This function describes the relationship between CME mass and flare flux
over at least 3 dex in flare flux, from ~10^-7 to 10^-4 W m^-2.Comment: 28 pages, 16 figures, accepted to Solar Physic
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