124 research outputs found
The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: SHARPs -- Space-weather HMI Active Region Patches
A new data product from the Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO) called Space-weather HMI Active Region
Patches (SHARPs) is now available. SDO/HMI is the first space-based instrument
to map the full-disk photospheric vector magnetic field with high cadence and
continuity. The SHARP data series provide maps in patches that encompass
automatically tracked magnetic concentrations for their entire lifetime; map
quantities include the photospheric vector magnetic field and its uncertainty,
along with Doppler velocity, continuum intensity, and line-of-sight magnetic
field. Furthermore, keywords in the SHARP data series provide several
parameters that concisely characterize the magnetic-field distribution and its
deviation from a potential-field configuration. These indices may be useful for
active-region event forecasting and for identifying regions of interest. The
indices are calculated per patch and are available on a twelve-minute cadence.
Quick-look data are available within approximately three hours of observation;
definitive science products are produced approximately five weeks later. SHARP
data are available at http://jsoc.stanford.edu and maps are available in either
of two different coordinate systems. This article describes the SHARP data
products and presents examples of SHARP data and parameters.Comment: 27 pages, 7 figures. Accepted to Solar Physic
On the solar wind control of cusp aurora during northward IMF
[1] The location of cusp aurora during northward interplanetary magnetic field (IMF) conditions and the solar wind control of that location are explored. The cusp aurora is imaged by the Imager for Magnetopause-to-Aurora Global Exploration\u27s (IMAGE) Far Ultraviolet Instrument (FUV). Predicted locations of the cusp aurora were computed by assuming anti-parallel reconnection between the observed IMF orientation and the 1996 Tsyganenko model magnetopause magnetic field. While the majority of anti-parallel reconnection sites tailward of the cusp, when mapped to the ionosphere, coincide with the observed cusp aurora, the anti-parallel merging hypothesis cannot explain certain aspects of the observations, including its location dependence with IMF + By
Flux Rope Formation Preceding Coronal Mass Ejection Onset
We analyse the evolution of a sigmoidal (S shaped) active region toward
eruption, which includes a coronal mass ejection (CME) but leaves part of the
filament in place. The X-ray sigmoid is found to trace out three different
magnetic topologies in succession: a highly sheared arcade of coronal loops in
its long-lived phase, a bald-patch separatrix surface (BPSS) in the hours
before the CME, and the first flare loops in its major transient intensity
enhancement. The coronal evolution is driven by photospheric changes which
involve the convergence and cancellation of flux elements under the sigmoid and
filament. The data yield unambiguous evidence for the existence of a BPSS, and
hence a flux rope, in the corona prior to the onset of the CME.Comment: ApJ Letters, in pres
Evidence For Mixed Helicity in Erupting Filaments
Erupting filaments are sometimes observed to undergo a rotation about the
vertical direction as they rise. This rotation of the filament axis is
generally interpreted as a conversion of twist into writhe in a kink-unstable
magnetic flux rope. Consistent with this interpretation, the rotation is
usually found to be clockwise (as viewed from above) if the post-eruption
arcade has right-handed helicity, but counterclockwise if it has left-handed
helicity. Here, we describe two non--active-region filament events recorded
with the Extreme-Ultraviolet Imaging Telescope (EIT) on the {\it Solar and
Heliospheric Observatory} ({\it SOHO}), in which the sense of rotation appears
to be opposite to that expected from the helicity of the post-event arcade.
Based on these observations, we suggest that the rotation of the filament axis
is in general determined by the net helicity of the erupting system, and that
the axially aligned core of the filament can have the opposite helicity sign to
the surrounding field. In most cases, the surrounding field provides the main
contribution to the net helicity. In the events reported here, however, the
helicity associated with the filament ``barbs'' is opposite in sign to and
dominates that of the overlying arcade.Comment: ApJ, accepte
Hyperdiffusion as a Mechanism for Solar Coronal Heating
A theory for the heating of coronal magnetic flux ropes is developed. The
dissipated magnetic energy has two distinct contributions: (1) energy injected
into the corona as a result of granule-scale, random footpoint motions, and (2)
energy from the large-scale, nonpotential magnetic field of the flux rope. The
second type of dissipation can be described in term of hyperdiffusion, a type
of magnetic diffusion in which the helicity of the mean magnetic field is
conserved. The associated heating rate depends on the gradient of the torsion
parameter of the mean magnetic field. A simple model of an active region
containing a coronal flux rope is constructed. We find that the temperature and
density on the axis of the flux rope are lower than in the local surroundings,
consistent with observations of coronal cavities. The model requires that the
magnetic field in the flux rope is stochastic in nature, with a perpendicular
length scale of the magnetic fluctuations of order 1000 km.Comment: 9 pages (emulateapj style), 4 figures, ApJ, in press (v. 679; June 1,
2008
A Method for Data-Driven Simulations of Evolving Solar Active Regions
We present a method for performing data-driven simulations of solar active
region formation and evolution. The approach is based on magnetofriction, which
evolves the induction equation assuming the plasma velocity is proportional to
the Lorentz force. The simulations of active region coronal field are driven by
temporal sequences of photospheric magnetograms from the Helioseismic Magnetic
Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO). Under
certain conditions, the data-driven simulations produce flux ropes that are
ejected from the modeled active region due to loss of equilibrium. Following
the ejection of flux ropes, we find an enhancement of the photospheric
horizontal field near the polarity inversion line. We also present a method for
the synthesis of mock coronal images based on a proxy emissivity calculated
from the current density distribution in the model. This method yields mock
coronal images that are somewhat reminiscent of images of active regions taken
by instruments such as SDO's Atmospheric Imaging Assembly (AIA) at extreme
ultraviolet wavelengths.Comment: Accepted to ApJ; comments/questions related to this article are
welcome via e-mail, even after publicatio
Heliophysics Discovery Tools for the 21st Century: Data Science and Machine Learning Structures and Recommendations for 2020-2050
Three main points: 1. Data Science (DS) will be increasingly important to
heliophysics; 2. Methods of heliophysics science discovery will continually
evolve, requiring the use of learning technologies [e.g., machine learning
(ML)] that are applied rigorously and that are capable of supporting discovery;
and 3. To grow with the pace of data, technology, and workforce changes,
heliophysics requires a new approach to the representation of knowledge.Comment: 4 pages; Heliophysics 2050 White Pape
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