297 research outputs found
Estimating Electric Fields from Vector Magnetogram Sequences
Determining the electric field (E-field) distribution on the Sun's
photosphere is essential for quantitative studies of how energy flows from the
Sun's photosphere, through the corona, and into the heliosphere. This E-field
also provides valuable input for data-driven models of the solar atmosphere and
the Sun-Earth system. We show how Faraday's Law can be used with observed
vector magnetogram time series to estimate the photospheric E-field, an
ill-posed inversion problem. Our method uses a "poloidal-toroidal
decomposition" (PTD) of the time derivative of the vector magnetic field. The
PTD solutions are not unique; the gradient of a scalar potential can be added
to the PTD E-field without affecting consistency with Faraday's Law. We present
an iterative technique to determine a potential function consistent with ideal
MHD evolution; but this E-field is also not a unique solution to Faraday's Law.
Finally, we explore a variational approach that minimizes an energy functional
to determine a unique E-field, similar to Longcope's "Minimum Energy Fit". The
PTD technique, the iterative technique, and the variational technique are used
to estimate E-fields from a pair of synthetic vector magnetograms taken from an
MHD simulation; and these E-fields are compared with the simulation's known
electric fields. These three techniques are then applied to a pair of vector
magnetograms of solar active region NOAA AR8210, to demonstrate the methods
with real data.Comment: 41 pages, 10 figure
The Effects of Rotation on the Evolution of Rising Omega-loops in a Stratified Model Convection Zone
We present three-dimensional MHD simulations of buoyant magnetic flux tubes
that rise through a stratified model convection zone in the presence of solar
rotation. The equations of MHD are solved in the anelastic approximation, and
the results are used to determine the effects of solar rotation on the dynamic
evolution an Omega-loop. We find that the Coriolis force significantly
suppresses the degree of fragmentation at the apex of the loop during its
ascent toward the photosphere. If the initial axial field strength of the tube
is reduced, then, in the absence of forces due to convective motions, the
degree of apex fragmentation is also reduced. We show that the Coriolis force
slows the rise of the tube, and induces a retrograde flow in both the
magnetized and unmagnetized plasma of an emerging active region.
Observationally, we predict that this flow will appear to originate at the
leading polarity, and will terminate at the trailing polarity.Comment: 25 pages, 8 figures, ApJ in pres
An Investigation of Salmonine Reproduction and Factors Limiting Their Production in Sandy Creek, Monroe County, New York
Sandy Creek is stocked annually with salmonines by the New York Department of Environmental Conservation. A good recreational fishery has been established during fall spawning migrations but spawning success and juvenile survival have not been researched. My study sought to 1) determine the extent of use of Sandy Creek by adult and juvenile salmonines in 2006 and 2007, 2) assess the creek\u27s potential for sustaining spawning and early life history requirements, and 3) estimate salmonine production in Sandy Creek and potential recruitment to Lake Ontario. Adult Chinook and coho salmon, brown trout and rainbow trout/steelhead were captured and spawned in Sandy Creek. Suitable spawning habitat is generally restricted to the upper reaches of Sandy Creek\u27s east and west branches because bedrock and mud substrates preclude redd construction elsewhere. Habitat and physiochemical conditions are conducive for healthy egg and larval development through winter and spring. Juvenile Chinook and coho salmon, brown trout and rainbow trout/steelhead caught in Sandy Creek were mostly in the east and west branches. Chinook salmon grew rapidly, reaching a total length of ~ 100 mm between emergence in March and out migration to Lake Ontario in June. Coho salmon and rainbow trout/steelhead occupied the headwater region of the east branch of Sandy Creek; few juvenile brown trout were captured. Water temperatures exceeded the upper thermal thresholds (\u3e28 °C) of most salmonine species throughout most of Sandy Creek during July and August. Areal extrapolation of CPUE suggests that Sandy Creek can produce ~ 6,900 juvenile salmonines/creek ha but only the headwater regions provide suitable habitat and physiochemical conditions for salmonine survival year round. Reforestation of the riparian zone and subsequent decreases in soil erosion and summer water temperature would increase salmonine production in Sandy Creek; however, the predominantly bedrock substrate prevents spawning in 90°/o of its main stem. Sandy Creek also supports a healthy, diverse warmwater fish community
Hard X-ray and UV Observations of the 2005 January 15 Two-ribbon Flare
In this paper, we present comprehensive analysis of a two-ribbon flare
observed in UV 1600{\AA} by Transition Region and Coronal Explorer and in HXRs
by Reuven Ramaty High Energy Solar Spectroscopic Imager. HXR (25-100 keV)
imaging observations show two kernels of size (FWHM) 15?? moving along the two
UV ribbons. We find the following results. (1) UV brightening is substantially
enhanced wherever and whenever the compact HXR kernel is passing, and during
the HXR transit across a certain region, the UV count light curve in that
region is temporally correlated with the HXR total flux light curve. After the
passage of the HXR kernel, the UV light curve exhibits smooth monotonical
decay. (2)We measure the apparent motion speed of the HXR sources and UV ribbon
fronts, and decompose the motion into parallel and perpendicular motions with
respect to the magnetic polarity inversion line (PIL). It is found that HXR
kernels and UV fronts exhibit similar apparent motion patterns and speeds. The
parallel motion dominates during the rise of the HXR emission, and the
perpendicular motion starts and dominates at the HXR peak, the apparent motion
speed being 10-40 km s-1. (3) We also find that UV emission is characterized by
a rapid rise correlated with HXRs, followed by a long decay on timescales of
15-30 minutes. The above analysis provides evidence that UV brightening is
primarily caused by beam heating, which also produces thick-target HXR
emission. The thermal origin of UV emission cannot be excluded, but would
produce weaker heating by one order of magnitude. The extended UV ribbons in
this event are most likely a result of sequential reconnection along the PIL,
which produces individual flux tubes (post-flare loops), subsequent non-thermal
energy release and heating in these flux tubes, and then the very long cooling
time of the transition region at the feet of these flux tubes.Comment: 8 figure
Simulation of Flux Emergence from the Convection Zone to the Corona
Here, we present numerical simulations of magnetic flux buoyantly rising from
a granular convection zone into the low corona. We study the complex
interaction of the magnetic field with the turbulent plasma. The model includes
the radiative loss terms, non-ideal equations of state, and empirical corona
heating. We find that the convection plays a crucial role in shaping the
morphology and evolution of the emerging structure. The emergence of magnetic
fields can disrupt the convection pattern as the field strength increases, and
form an ephemeral region-like structure, while weak magnetic flux emerges and
quickly becomes concentrated in the intergranular lanes, i.e. downflow regions.
As the flux rises, a coherent shear pattern in the low corona is observed in
the simulation. In the photosphere, both magnetic shearing and velocity
shearing occur at a very sharp polarity inversion line (PIL). In a case of
U-loop magnetic field structure, the field above the surface is highly sheared
while below it is relaxed
Sewage disposal improvements at Pontiac, Michigan
The existing East Boulevard Sewage Disposal Plant consists of a set of bar screens, a grit chamber, a battery of three Imhoff tanks, eight trickling filter units, of the rotary-distributor type, and three secondary settling tanks. The plant was designed for a population of 52,500 in 1919 by Clarence W. Hubbell, Consulting Engineer. At the present time the plant shows evidence of loading beyond its capacity, the distress of the Imhoff tanks being particularly acute --Present Sewage Disposal Facilities, page 5
Buildup of Magnetic Shear and Free Energy During Flux Emergence and Cancellation
We examine a simulation of flux emergence and cancellation, which shows a
complex sequence of processes that accumulate free magnetic energy in the solar
corona essential for the eruptive events such as coronal mass ejections (CMEs),
filament eruptions and flares. The flow velocity at the surface and in the
corona shows a consistent shearing pattern along the polarity inversion line
(PIL), which together with the rotation of the magnetic polarities, builds up
the magnetic shear. Tether-cutting reconnection above the PIL then produces
longer sheared magnetic field lines that extend higher into the corona, where a
sigmoidal structure forms. Most significantly, reconnection and upward
energy-flux transfer are found to occur even as magnetic flux is submerging and
appears to cancel at the photosphere. A comparison of the simulated coronal
field with the corresponding coronal potential field graphically shows the
development of nonpotential fields during the emergence of the magnetic flux
and formation of sunspots
Dynamic Coupling of Convective Flows and Magnetic Field during Flux Emergence
We simulate the buoyant rise of a magnetic flux rope from the solar
convection zone into the corona to better understand the energetic coupling of
the solar interior to the corona. The magnetohydrodynamic model addresses the
physics of radiative cooling, coronal heating and ionization, which allow us to
produce a more realistic model of the solar atmosphere. The simulation
illustrates the process by which magnetic flux emerges at the photosphere and
coalesces to form two large concentrations of opposite polarities. We find that
the large-scale convective motion in the convection zone is critical to form
and maintain sunspots, while the horizontal converging flows in the near
surface layer prevent the concentrated polarities from separating. The foot
points of the sunspots in the convection zone exhibit a coherent rotation
motion, resulting in the increasing helicity of the coronal field. Here, the
local configuration of the convection causes the convergence of opposite
polarities of magnetic flux with a shearing flow along the polarity inversion
line. During the rising of the flux rope, the magnetic energy is first injected
through the photosphere by the emergence, followed by energy transport by
horizontal flows, after which the energy is subducted back to the convection
zone by the submerging flows
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