28 research outputs found
Can we Determine Electric Fields and Poynting Fluxes from Vector Magnetograms and Doppler Measurements?
The availability of vector magnetogram sequences with sufficient accuracy and
cadence to estimate the time derivative of the magnetic field allows us to use
Faraday's law to find an approximate solution for the electric field in the
photosphere, using a Poloidal-Toroidal Decomposition (PTD) of the magnetic
field and its partial time derivative. Without additional information, however,
the electric field found from this technique is under-determined -- Faraday's
law provides no information about the electric field that can be derived the
gradient of a scalar potential. Here, we show how additional information in the
form of line-of-sight Doppler flow measurements, and motions transverse to the
line-of-sight determined with ad-hoc methods such as local correlation
tracking, can be combined with the PTD solutions to provide much more accurate
solutions for the solar electric field, and therefore the Poynting flux of
electromagnetic energy in the solar photosphere. Reliable, accurate maps of the
Poynting flux are essential for quantitative studies of the buildup of magnetic
energy before flares and coronal mass ejections.Comment: Solar Physics, in press. 14 pages, 3 figure
Triggering an eruptive flare by emerging flux in a solar active-region complex
A flare and fast coronal mass ejection originated between solar active
regions NOAA 11514 and 11515 on July 1, 2012 in response to flux emergence in
front of the leading sunspot of the trailing region 11515. Analyzing the
evolution of the photospheric magnetic flux and the coronal structure, we find
that the flux emergence triggered the eruption by interaction with overlying
flux in a non-standard way. The new flux neither had the opposite orientation
nor a location near the polarity inversion line, which are favorable for strong
reconnection with the arcade flux under which it emerged. Moreover, its flux
content remained significantly smaller than that of the arcade (approximately
40 %). However, a loop system rooted in the trailing active region ran in part
under the arcade between the active regions, passing over the site of flux
emergence. The reconnection with the emerging flux, leading to a series of jet
emissions into the loop system, caused a strong but confined rise of the loop
system. This lifted the arcade between the two active regions, weakening its
downward tension force and thus destabilizing the considerably sheared flux
under the arcade. The complex event was also associated with supporting
precursor activity in an enhanced network near the active regions, acting on
the large-scale overlying flux, and with two simultaneous confined flares
within the active regions.Comment: Accepted for publication in Topical Issue of Solar Physics: Solar and
Stellar Flares. 25 pages, 12 figure
A model for the importance of large arborescent palms in the dynamics of seasonally-dry amazonian forests
Observables Processing for the Helioseismic and Magnetic Imager Instrument on the Solar Dynamics Observatory
The Helioseismic and Magnetic Imager (HMI) Investigation for the Solar Dynamics Observatory (SDO)
Theory, simulation, and observation of discrete eigenmodes associated with lower hybrid solitary structures
International audienceA three-dimensional fluid description of nonlinear lower hybrid waves is investigated in the context of plasma density depletions. The objective is a basic understanding of lower hybrid solitary structures associated with transverse ion acceleration in the topside auroral ionosphere. The equations are linearized about a parabolic density depletion and solved. The solution consists of potential structures (eigenfunctions) which rotate in angle about the center of the density depletion. The eigenfrequencies are discrete for Iwl • w•. These eigenfunctions rotate in a left-handed sense about the geomagnetic field and the solutions fall off exponentially outside the density depletion. The eigenfrequencies are continuous for Iwl • w•a and kz • 0 but become discrete for kz-0 in agreement with previous two-dimensional results [Seyler, 1994]. Simulations of the full nonlinear system are performed, and rotating eigenmodes are extracted from the spectrum. The results agree with the analytic results obtained from the linearized equations. The spectral properties of a lower hybrid solitary structure from the TOPAZ III sounding rocket are reexamined and found to be consistent with theoretical predictions for lower hybrid waves trapped within a density depletion as presented herein. A local wavelet frequency-wavenumber spectrum is constructed from data taken by moving an interferometer through a simulation at a typical rocket velocity. The results compare favorably with the local frequency-wavenumber spectrum of a lower hybrid solitary structure observed by the TOPAZ II! sounding rocket