16 research outputs found
Evolution of reconnection along an arcade of magnetic loops
RHESSI observations of a solar flare showing continuous motions of double
hard X-ray sources interpreted as footpoints of magnetic loops are presented.
The temporal evolution shows many distinct emission peaks of duration of some
tens of seconds ('elementary flare bursts'). Elementary flare bursts have been
interpreted as instabilities or oscillations of the reconnection process
leading to an unsteady release of magnetic energy. These interpretations based
on two-dimensional concepts cannot explain these observations, showing that the
flare elements are displaced in a third dimension along the arcade. Therefore,
the observed flare elements are not a modulation of the reconnection process,
but originate as this process progresses along an arcade of magnetic loops.
Contrary to previous reports, we find no correlation between footpoint motion
and hard X-ray flux. This flare apparently contradicts the predictions of the
standard translation invariant 2.5D reconnection models.Comment: 4 pages, 3 figures, to be published in Astrophysical Journal Letter
Electron acceleration in solar flares: observations versus numerical simulations
We use RHESSI hard X-ray observations to constrain acceleration of solar flare electrons, generally considered to be a primary recipient of the released energ
Survey on Solar X-ray Flares and Associated Coherent Radio Emissions
The radio emission during 201 selected X-ray solar flares was surveyed from 100 MHz to 4 GHz with the Phoenix-2 spectrometer of ETH ZĂĽrich. The selection includes all RHESSI flares larger than C5.0 jointly observed from launch until June 30, 2003. Detailed association rates of radio emission during X-ray flares are reported. In the decimeter wavelength range, type III bursts and the genuinely decimetric emissions (pulsations, continua, and narrowband spikes) were found equally frequently. Both occur predominantly in the peak phase of hard X-ray (HXR) emission, but are less in tune with HXRs than the high-frequency continuum exceeding 4 GHz, attributed to gyrosynchrotron radiation. In 10% of the HXR flares, an intense radiation of the above genuine decimetric types followed in the decay phase or later. Classic meter-wave type III bursts are associated in 33% of all HXR flares, but only in 4% are they the exclusive radio emission. Noise storms were the only radio emission in 5% of the HXR flares, some of them with extended duration. Despite the spatial association (same active region), the noise storm variations are found to be only loosely correlated in time with the X-ray flux. In a surprising 17% of the HXR flares, no coherent radio emission was found in the extremely broad band surveyed. The association but loose correlation between HXR and coherent radio emission is interpreted by multiple reconnection sites connected by common field line
Observations and Interpretation of a Low Coronal Shock Wave Observed in the EUV by the SDO/AIA
Taking advantage of both the high temporal and spatial resolution of the
Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory
(SDO), we studied a limb coronal shock wave and its associated extreme
ultraviolet (EUV) wave that occurred on 2010 June 13. Our main findings are (1)
the shock wave appeared clearly only in the channels centered at 193 \AA and
211 \AA as a dome-like enhancement propagating ahead of its associated
semi-spherical CME bubble; (2) the density compression of the shock is 1.56
according to radio data and the temperature of the shockis around 2.8 MK; (3)
the shock wave first appeared at 05:38 UT, 2 minutes after the associated flare
has started and 1 minute after its associated CME bubble appeared;(4) the top
of the dome-like shock wave set out from about 1.23 R\odot and the thickness of
the shocked layer is ~ 2\times10^4 km; (5) the speed of the shock wave is
consistent with a slight decrease from about 600 km/s to 550 km/s; (6) the
lateral expansion of the shock wave suggests a constant speed around 400 km/s,
which varies at different heights and directions. Our findings support the view
that the coronal shock wave is driven by the CME bubble, and the on-limb EUV
wave is consistent with a fast wave or at least includes the fast wave
component.Comment: 24 pages,8 Figures and 6 movies. It is scheduled for publication on
the Astrophysical Journal on the August 1, 2011, Issue 736 -
Survey on solar X-ray flares and associated coherent radio emissions
The radio emission during 201 X-ray selected solar flares was surveyed from
100 MHz to 4 GHz with the Phoenix-2 spectrometer of ETH Zurich. The selection
includes all RHESSI flares larger than C5.0 jointly observed from launch until
June 30, 2003. Detailed association rates of radio emission during X-ray flares
are reported. In the decimeter wavelength range, type III bursts and the
genuinely decimetric emissions (pulsations, continua, and narrowband spikes)
were found equally frequently. Both occur predominantly in the peak phase of
hard X-ray (HXR) emission, but are less in tune with HXRs than the
high-frequency continuum exceeding 4 GHz, attributed to gyrosynchrotron
radiation. In 10% of the HXR flares, an intense radiation of the above genuine
decimetric types followed in the decay phase or later. Classic meter-wave type
III bursts are associated in 33% of all HXR flares, but only in 4% they are the
exclusive radio emission. Noise storms were the only radio emission in 5% of
the HXR flares, some of them with extended duration. Despite the spatial
association (same active region), the noise storm variations are found to be
only loosely correlated in time with the X-ray flux. In a surprising 17% of the
HXR flares, no coherent radio emission was found in the extremely broad band
surveyed. The association but loose correlation between HXR and coherent radio
emission is interpreted by multiple reconnection sites connected by common
field lines.Comment: Solar Physics, in pres