12 research outputs found
Zones with quasi-discontinuous magnetic connections in the photosphere and solar flares
The topological structure of active regions is related with flare brightening. (Mandrini et a!, 1991, 1993; Démoulin et ai, 1992, 1993, 1994). In these works, we modeled the observed longitudinal magnetic field by means of a discrete number of sub-photospheric magnetic poles, and derived the magnetic topology taking into account the connections between these poles (source method, MF). We present here a new method (quasi-discontinuity method, MQD). It finds the regions above the photosphere where the connectivity of field lines changes drastically.Asociación Argentina de Astronomí
Homologous Flares and Magnetic Field Topology in Active Region NOAA 10501 on 20 November 2003
We present and interpret observations of two morphologically homologous
flares that occurred in active region (AR) NOAA 10501 on 20 November 2003. Both
flares displayed four homologous H-alpha ribbons and were both accompanied by
coronal mass ejections (CMEs). The central flare ribbons were located at the
site of an emerging bipole in the center of the active region. The negative
polarity of this bipole fragmented in two main pieces, one rotating around the
positive polarity by ~ 110 deg within 32 hours. We model the coronal magnetic
field and compute its topology, using as boundary condition the magnetogram
closest in time to each flare. In particular, we calculate the location of
quasiseparatrix layers (QSLs) in order to understand the connectivity between
the flare ribbons. Though several polarities were present in AR 10501, the
global magnetic field topology corresponds to a quadrupolar magnetic field
distribution without magnetic null points. For both flares, the photospheric
traces of QSLs are similar and match well the locations of the four H-alpha
ribbons. This globally unchanged topology and the continuous shearing by the
rotating bipole are two key factors responsible for the flare homology.
However, our analyses also indicate that different magnetic connectivity
domains of the quadrupolar configuration become unstable during each flare, so
that magnetic reconnection proceeds differently in both events.Comment: 24 pages, 10 figures, Solar Physics (accepted
Origin of the submillimeter radio emission during the time-extended phase of a solar flare
Solar flares observed in the 200-400 GHz radio domain may exhibit a slowly
varying and time-extended component which follows a short (few minutes)
impulsive phase and which lasts for a few tens of minutes to more than one
hour. The few examples discussed in the literature indicate that such
long-lasting submillimeter emission is most likely thermal bremsstrahlung. We
present a detailed analysis of the time-extended phase of the 2003 October 27
(M6.7) flare, combining 1-345 GHz total-flux radio measurements with X-ray,
EUV, and H{\alpha} observations. We find that the time-extended radio emission
is, as expected, radiated by thermal bremsstrahlung. Up to 230 GHz, it is
entirely produced in the corona by hot and cool materials at 7-16 MK and 1-3
MK, respectively. At 345 GHz, there is an additional contribution from
chromospheric material at a few 10^4 K. These results, which may also apply to
other millimeter-submillimeter radio events, are not consistent with the
expectations from standard semi-empirical models of the chromosphere and
transition region during flares, which predict observable radio emission from
the chromosphere at all frequencies where the corona is transparent.Comment: 27 pages, 7 figure
The Origin, Early Evolution and Predictability of Solar Eruptions
Coronal mass ejections (CMEs) were discovered in the early 1970s when space-borne coronagraphs revealed that eruptions of plasma are ejected from the Sun. Today, it is known that the Sun produces eruptive flares, filament eruptions, coronal mass ejections and failed eruptions; all thought to be due to a release of energy stored in the coronal magnetic field during its drastic reconfiguration. This review discusses the observations and physical mechanisms behind this eruptive activity, with a view to making an assessment of the current capability of forecasting these events for space weather risk and impact mitigation. Whilst a wealth of observations exist, and detailed models have been developed, there still exists a need to draw these approaches together. In particular more realistic models are encouraged in order to asses the full range of complexity of the solar atmosphere and the criteria for which an eruption is formed. From the observational side, a more detailed understanding of the role of photospheric flows and reconnection is needed in order to identify the evolutionary path that ultimately means a magnetic structure will erupt