ar059.schmieder02
Posted: 25-Oct-93
Updated: 24-Jul-94, 03-Apr-95, 17-Jan-96
Events specified: AR 7493, 7494, 7497 (Emerging flux region and related activity)
Category: AR evolution (emerging flux) and chromospheric ejections
PI and Collaborators: Schmieder B., Kurokawa H., Kawai G.,
Mein P. and N., van Driel-Gesztelyi L.,
N. Nitta, and who is interested in this topics.
Motivation: It is well known that emerging flux in active regions leads to
the formation of arch filament system due to compression of the
plasma above the emerging flux. The formation of arch filament
has been studied by e.g. Georgakilas etal (1993,
Solar Physics 146,241).
The common altitude of H-alpha arches is between 5000 km to 12000
km. The interaction of an emerging flux with the pre-existing
magnetic fields is known to be associated with different kinds of
chromospheric eruptions:
(i) The appearance of an emerging flux close to the footpoints of a
filament frequently leads to the activation or eruption of the
filament (e.g. Schmieder etal 1986, Astron. Astrophys.).
(ii) If the new magnetic flux appears in a region of opposite
polarity, the resulting magnetic configuration can become quite
complex which is favourable for surge activity.
In fact surge or ejection of material is commonly observed with
its base tied along the inversion line of this isolated magnetic
island, called parasitic or satellite polarity.
These events may have different signatures in soft X-ray:
arch system, jet, eruption: all of these are good diagnostics of
the field line topology. The relationship between cold and hot
plasma events can be modelized if quantitative values are obtained.
Data and Method to be Used:
The combination of Hida, Meudon, and Canary Islands observations
allows to follow the evolution of an emerging flux region in
H-alpha over more than 24 hours. Hida Observatory filtergrams have
a large field of view and would be very useful for the coalignement
of the data. The Multichannel Double Pass Spectrograph (MSDP)
operating at Meudon and in Teneriffe on the VTT provides the
dynamics of the events. The comparison of the H-alpha observations
with the Yohkoh SXT images would provide a diagnostics of the
relationship between the chromospheric an the coronal
events.
DATA Available during the coordinated campaign:
AR 7493 (S10,E29) May 1 1993 surge observed in H\alpha
magnetograms of Potsdam for May 1 (0716-0734)
and May 2
AR 7493 (S10 W 38) data of May 4 1993 decreasing of the arch
filament system during a period of 10 hours.
AR 7497 (S08 W50) May 5 and May 6 1993 : complex active region
with a new p spot, a surge and an activated
filament. magnetogram in Meudon
AR 7496 (N17 E65) May 6 Meudon and Teneriffe: activated large
filament
Update 17-Jan-96
We are mainly working on data on the 1 and 2 May 1993.
We have presented some results along our study in 3 meetings and publish one paper in solar physics:
"Emerging Flux, reconnection, and XNP: Observations meet theory" van Driel L. etal 1995 IAU colloquium 153, Makuhari
X bright points" : van Driel L.: 1995 JOSO meeting in Czech Republic
X ray bright point flare due to magnetic reconnection" van Driel et al: 1995, Solar Physics in press
We are working on a new paper. Here the draft of the abstract:
3D Magnetic Reconnection at an X-ray Bright Point
C. H. Mandrini$^{1}$, P. D\'{e}moulin$^{2}$, L. van Driel-Gesztelyi$^{2}$, B. Schmieder$^{2}$,\\ G. Cauzzi$^{3}$ and A. Hofmann$^{4}$ \vspace{1.5cm}\\
{\scriptsize 1} Instituto de Astronom\'{\i}a y F\'{\i}sica del Espacio, IAFE-CONICET, CC.67, Suc.28, 1428 Buenos Aires, Argentina
Abstract
A flaring X-ray bright point (XBP) was observed for about 16 hours in the old, disintegrating, bipolar active region (AR) NOAA 7493 on May 1, 1993, where a minor new bipole emerged ($10^{20}$ Mx). The XBP was located between the new negative polarity field and a pre-existing positive polarity plage region. The position of the XBP shifted during its lifetime in such a way that it followed the new field, that moved with a velocity of 0.2 \kms, thus the XBP always remained between the new and the pre-existing field. We have found observational evidences showing that the XBP brightenings were due to magnetic reconnection between the new bipole and the pre-existing plage fields, being this process induced by the motion of the new negative polarity pore towards the plage. The aim of this work is to substantiate from magnetic modelling what has been shown by the observations. For this purpose we extrapolate the observed photospheric magnetic field in the linear force-free approximation and follow its evolution during the XBP lifetime. From the computed coronal field lines we determine the location of regions of drastic change in field-line linkage, called ``quasi-separatrix layers'' or QSLs. QSLs are open layers that behave physically like separatrices: the breakdown of ideal MHD and the release of free magnetic energy may occur at these locations when their thickness is small enough. We find field lines, whose photospheric footpoints lie at both sides of QSLs, in good agreement with the observations of emerging flux (in H$\alpha$) and bright X-ray loops. We study also the evolution of the width of the QSL located along the new negative polarity pore and find that it is very thin (typically 100 m) during the XBP lifetime, while this QSL becomes much thicker ($\geq 10^5$ m) after the XBP has faded. These results strongly support the fact that the XBP brightenings are due to the interaction of different flux systems, through 3D reconnection, at QSLs.\\
Update 03-Apr-95
As the result of the proposal a paper has been submitted to Solar Physics (see abstract below), but we are still working on the observations, the present project includes the extrapolation of the coronal field lines, comparison between the observed and computed connectivities and between the observed flare kernels and computed places of separators, where magnetic field line reconnection is expected to occur.
Title: X-Ray Bright Point Flares Due to Magnetic Reconnection
Authors: L. van Driel-Gesztelyi, B. Schmieder, G. Cauzzi, N. Mein, A. Hofmann, N. Nitta, H. Kurokawa, P. Mein, and J. Staiger
Abstract: Ground-based optical observations coordinated with Yohkoh/SXT X-ray observations of AR NOAA 7493 (May 1, 1993) provided a multiwavelength data base allowing a study of a flaring X-ray bright point (XBP) of about 16 hours lifetime, and the activity related to it in different layers of the solar atmosphere. We found observational evidence showing that XBP brightenings do not form a separated class of events, but that they are merely very small flares due to reconnection of magnetic field lines. Utilising magnetograms taken every 6 hours we followed the emergence and motion of a small (N) and (S) bipole in an environment of positive magnetic polarity. H-alpha observations showed the development of a chromospheric arch filament system connecting the opposite polarity pores of the new bipole, as well as chromospheric faculae, or plages in the vicinity of the footpoints and surge events. The XBP appeared in the corona between the negative polarity new pore (S) and a pre-existing positive polarity plage (NF), and as (S) moved with a velocity of 0.2 km/s, the XBP shifted in such a way that it remained between (S) and (NF). The XBP, superposed on a global evolution of soft X-ray brightness, displayed changes of brightness, interpreted as microflares, lasting for 1-10 minutes. During the microflares the XBP apparently had a spatial structure, which was rather (tiny) loop-like than point-like. The XBP microflares were correlated with chromospheric activity: (i) brightenings of underlying chromospheric faculae, and (ii) appearance of strong turbulent velocities in the arch filament system. We propose that the XBP microflares were due to reconnection of the magnetic field lines (sketched in 3D) between the new bipole and the pre-existing plage fields induced by the motion of the new (S) pore towards plage (NF), and that the XBP itself was the reconnected hot loop between (S) and (NF).
Update 24-Jul-94
Following is the abstract of a paper to be presented at COSPAR, July 1994 (Symposium E2.2). Both the Oct 91 and May 93 events seem to be associated with emerging flux.
CHROMOSPHERIC EJECTIONS AND THEIR SIGNATURES IN X-RAY OBSERVED BY YOHKOH
B. Schmieder and N Mein (Observatoire de Paris, Section de Meudon, URA 326, 92195 Meudon Cedex Principal, France)
S. Freeland (Lockheed Palo Alto Research Laboratory, Palo Alto, CA 94304, USA)
K. Shibata (National Astronomical Observatory, Mitaka, Tokyo 181, Japan)
L. van Driel-Gesztelyi (Kiso Observatory, University of Tokyo, Mitake-mura, Kiso, Nagano 397-01, Japan
H.Kurokawa (Kwasan and Hida Observatories, Kyoto University, Kamitakara, Gifu 506-13, Japan)
Surge or ejection of chomospheric material is commonly observed in active regions with its base tied along the inversion line of this isolated magnetic island, called parasitic polarity (as seen in magnetograms from Huairou, MSFC, Hawai, Okayama). Using observations obtained during coordinated campaigns between the Yohkoh satellite and the Multichannel Subtractive Double Pass Instruments operating at Meudon and on the Canary Islands we are able to observe surge events (Oct 7 1991, May 1 1993) and look for their signatures in soft X-rays. In the partial frame images of Yohkoh SXT low X-ray loops overlaying the active region where the surge occurs are seen continuously restructuring. No X-ray emission is detected along the path of the surges and no X-ray jets are observed. X-ray bright points appear at the basis of the surge 5 minutes before the ejections, which have been interpreted as being due to magnetic reconnection. Cold plasma bubbles squeezed between magnetic field lines could correspond to surge material.