fl167.schmieder03 Posted: 26-Dec-93 Updated: 24-Mar-94, 29-Nov-94, 3-Sep-95, 18-May-96 Events specified: Post-flare loops observed on June 25 and 26, 1992
PI and Collaborators: Authorship: Schmieder B. (1), Heinzel P. (2) Kotrc P. (2), Wiik J.E. (3), Hiei (4), Anwar B.(5), Lemen J. (6) Yohkoh SXT-team investigators who have an interest (?)
(1) Observatoire de Paris, Section Meudon, 92195 Meudon, France\\ (2) Astronomical Institute, 25165 Ondrejov, Czech Republic\\ (3) ESTEC, Holland \\ (4) Meisei University, Tokyo\\ (5) National Institute of Aeronautics and Space, Bandung, Indonesia (6) Lockheeed Palo Alto, Research Lab, Palo Alto, USA.
We plan to analyze the physical conditions of the plasma in post-flare loops, both hot (SXT-data) and cool (optical ground-based data), with special emphasis to dynamics and energy transport.
Same flares may be analyzed by fl063.bachtiar02 fl137.hanaoka08. Please contact with those projects, if you proceed.
Motivation:
By using NLTE program developed in Ondrejov, plasma parameters will be derived from MSDP and Ondrejov spectra: electron density, gas pressure and temperature. Special attention will be devoted to check a new idea concerning soft X-ray irradiation of cool loops and their partial heating and ionization due to this process.
The MHD modeling of cool flare loops will be performed and the free fall model will be tested. The material along the Halpha loops is not homogeneous. Bubbles of material are flowing down. It may be related to the fragmentation of the energy release at the top of the loops. In the future it may be interesting to collaborate with team of BCS and HXT to see any signature of such fragmentation in higher energy bands.
Data to be used:
Spectra obtained in various optical lines (Balmer lines of HI, CaII H and K lines, helium line D3). The Multichannel Flare Spectrograph (MFS) in Ondrejov was operating during the period of MSDP observations, taking the spectra (spatial resolution around 2-3" due to seeing, dispersion 1A/mm) and CCD slit-jaw video images of H-alpha loops.
Method:
Publication:
Update 18-May-96
We made the following progress:
(i) We published two articles in Solar Physics on this post-flare loop system:
(1) Schmieder, B., Heinzel, P., van Driel-Gesztelyi, L., and Lemen, J.R.: 1996, 'Post-Flare Loops of 26 June 1992 II. Gradual Evolution of Cool and Hot Loops', Solar Physics 165, 303-328.
(2) Wiik, J.E., Schmieder, B., Heinzel, P., and Roudier, T.: 1996, Paper III. Solar Physics, in press
(ii) We collected H-alpha observations of the post-flare loop system from all around the world and measured the evolution of the altitude of hot X-ray and cool H-alpha loops as a function of time for more than 15 hours. We presented the results at two meetings, namely at the Yohkoh meeting at Bath, England (March 96) and during the Workshop on 3D Magnetic Field extrapolation in Huntsville, USA (May 96). The abstract to be submitted soon is as follows:
POST-FLARE LOOPS IN X-RAYS AND IN H$\alpha$ IV. FORMATION
L. van Driel-Gesztelyi, J.E. Wiik, B. Schmieder, R.Kitai, B. Anwar, T.Tarbell
Observations of the post-flare loops for more than 15 hours after the X3.9 flare on 25 June 1992 at 20:11 UT by the Yohkoh/SXT in X-rays, as well as in H$\alpha$ at Hida Observatory (Japan), Wroclaw (Poland) Vala\v{s}sk\'{e} Mezi\v{r}\v{\i}ci (Czech Republic), and LaPalma (Canaries) and with the Multi-channel Subtractive Double Pass spectrograph (MSDP) at Pic du Midi (France) provides a unique set of data for a study of the relationship between the hot and cool post-flare loops as they evolve. Cooling time is investigated versus time. Through a study of the magnetic configuration in which the flare occurred, we are able to reconstruct the true, 3D geometry of the loops and provide a set of relative altitude data. Such results are used to check the relevance of the reconnection model.
Update 3-Sep-95
This topics led to 2 new papers
authors: B. SCHMIEDER, P. HEINZEL, L. VAN DRIEL-GESZTELYI, J.E. WIIK
Observatoire de Paris, Section Meudon, 92195 Meudon, France
and J. LEMEN
Lockheed Palo Alto Research Laboratory, Palo Alto, CA 94304-1911, USA
Using coordinated observations of a large system of post-flare loops
on 25-26 June 1992, we studied the gradual formation and dynamics
of the loops and the relationship between hot X-ray and cool H$\alpha$ loops.
{\it Yohkoh/SXT} observed these loops for more than 14 hours (after the large
X-class flare of June 25 at 20:11 UT), and between 7:00 - 9:40 UT we have
obtained also H$\alpha$ spectra with the MSDP on Pic-du-Midi. From a
coalignment analysis between X-ray and H$\alpha$ images we see that the cool
loops are situated just below the hot ones and that the whole system grows up
with the velocity of about 1 km s$^{-1}$ (Schmieder {\it et al.} 1995 a).
This is explained by a gradual reconnection process as suggested by Forbes
and Malherbe (1986).
For the whole gradual phase, we have determined the temperature and the emission measure $EM$ from the SXT data (using two Al-filters). $EM$ was also computed for the cool H$\alpha$ loops. Estimating the thickness of cool loops to be around 2000 km (MSDP images) and taking into account the fact that SXT loops are more extended, we computed the electron densities $n_{e}$ in hot and cool plasmas. We found $n_{e}^{hot} \leq n_{e}^{cool} \simeq 2 \times 10^{10}$ cm$^{-3}$, at the time of the H$\alpha$ observations. However, from the temporal
evolution of the $EM$ we see that
$n_{e}^{hot} \simeq 5 \times 10^{10} - 10^{11}$ cm$^{-3}$ at around 0:00 UT and
$n_{e}^{hot} \simeq 5 \times 10^{9} - 10^{9}$ cm$^{-3}$ at the end of
the gradual phase (around 13:00 UT). The $EM$ itself decreased by almost
two orders of magnitude during the same period. Using these densities, we computed lower limits
of the cooling time which increases from several minutes at the beginning
to more than 2 hours at the end of the gradual phase of the flare
(Schmieder {\it et al.} 1995 b).
As a next step, we analysed in detail the dynamics of cool H$\alpha$ loops, using the MSDP data. After a geometrical reconstruction of the true shape of the loops we have derived the flow velocities of the cool plasma blobs. At the upper part of the loops we observed a free-fall motion, while in the lower parts of the legs the blobs seem to be decelerated and the flow velocity appeared to be almost constant. Several possible mechanisms for such a deceleration are discussed in a recent paper by Wiik {\it et al.} (1995) devoted to the dynamics of cool post-flare loops.
\begin{thebibliography}{} \bibitem{} Forbes, T.G. and Malherbe, J.M.(1986) Reconnection Process, {\it Astrophys.J.}, {\bf 302}, L67. \bibitem{} Schmieder, B, Heinzel, P., Wiik, J.E., Lemen, J.R., Anwar, B., Kotr\v{c}, P. Hiei, E. (1995a) Relation between cool and hot post-flare loops of June1992, {\it Solar Phys.}, {\bf 156}, 337. \bibitem{} Schmieder, B., Heinzel, P., van Driel-Gesztelyi, L., Lemen, J.R. (1995b), Gradual Evolution of cool and Hot Loops, {\it Solar Phys.}, submitted. \bibitem{} Wiik, J.E., Schmieder, B., Heinzel, P., Roudier, T. (1994), Dynamics and Inhomogeneities in Cool Flare Loops, {\it Solar Phys.}, submitted. \end{thebibliography}
$^{1}$Observatoire de Paris, Section de Meudon, F-92195 Meudon Principal Cedex, France, $^{2}$Astronomical Institute, CZ-25165 Ond\v{r}ejov, Czech Republic, $^{3}$Lockheed Palo Alto Research Lab., Palo Alto, Ca., USA.
Abstract:
We observed the large post-flare loop system that developed after the X 3.9 flare of 25 June 1992 at 20:11 UT in \ha\ with the Multichannel Subtractive Double Pass Spectrograph at Pic-du-Midi and in X-rays with the {\it YOHKOH/\-SXT} instrument. Following the long term development of cool and hot plasmas, we have determined the emission measure of the cool plasma and, for the first time, the temporal evolution of the hot-loop emission measure and temperature during the entire gradual phase. Thus, it was possible to infer the temporal variation of electron densities, providing us estimates of cooling times. A gradual decrease of the hot-loop emission measure was observed, from 4 $\times 10^{30}$ cm$^{-5}$ at 23:00 UT on 25 June 1992 to $ 3 \times 10^{28}$ cm$^{-5}$ at 13:10 UT on 26 June 1992. During the same period, the temperature decreased only slowly from 7.2 to 6.0 $10^{6}$ K. Using recent results of NLTE modeling of prominence-like plasmas, we also derive the emission measure of cool \ha\ loops and discuss their temperature and ionisation degree. During two hours of \ha\ observations (11-13 hours after the flare) the averaged emission measure does not show any significant change, though the amount of visible cool material decreases, and the volume of the loops increases. The emission measure in \ha , after correction for the Doppler-brightening effect, is slightly lower than in soft X-rays. Since the hot plasma seems to be more spatially extended, we arrive at electron densities in the range $n_{e}^{hot} \leq n_{e}^{cool} \simeq 2 \times 10^{10}$ cm $^{-3}$ at the time of the \ha\ observations.
These results are consistent with the post-flare loop model proposed by Forbes, Malherbe and Priest (1989). The observed slow decrease of the emission measure could be due to an increase of the volume of the loops and a gradual decrease of the chromospheric ablation driven by the reconnection, which seems to remain effective continuously for more than 16 hours. The cooling time for hot loops to become cool ones (10$^4$K) and appear in \ha\ would be only a few minutes at the beginning of the gradual phase but could be as long as 2 hours by the end, several hours later.
We plan to continue to work on this event by analysing Hard X-ray data. May we ask you not to supress this proposal. It is _always_ active.
Update 29-Nov-94
here the abstract of the paper accepted in Solar Physics.
Relationship between cool and hot post-flare loops of 26 June 1992 derived from optical and X-ray (SXT-Yohkoh) observations
B. Schmieder 1 and P. Heinzel 2 and J. E. Wiik 3 and J. Lemen 4 and B. Anwar 5 and P. Kotr\v{c} 2 and E. Hiei 6
1. Observatoire de Paris, Section de Meudon, F-92195 Meudon Principal Cedex, France 2.Astronomical Institute of the Czech Academy of Sciences, CZ-251 65 Ond\v{r}ejov, Czech Republic 3.ESA Space Science Department, Solar System Division (SO), ESTEC Postbus 299, NL-2200 AG Noordwijk, The Netherlands 4.Lockheed Palo Alto Research Lab., Palo Alto, USA 5.Ionospheric R and D Center, Lapan, J1.Dr Junjuan 133 Bandung 40173, Indonesia 6. Meisei University, NAO, 2-1-1, Hodokubo, Hino, 191 Tokyo, Japan
accepted for publication to Solar Physics on Sept 1994
Abstract
We have analyzed the physical conditions of the plasma in post-flare loops with special emphasis on dynamics and energy transport using SXT-data (hot plasma) and optical ground-based data from Pic du Midi, Wroc\l aw, and Ond\v{r}ejov (cool plasma). By combining the \ha\ observations with the SXT images we can understand the relationship between cool and hot plasmas, the process of cooling post-flare loops and the mechanism which maintains the long duration of these loops. Using recent results of NLTE modeling of prominence-like plasmas, we derive the emission measure of cool \ha\ loops and this gives us a realistic estimate of the electron density ($2.2\times 10^{10}$ cm $^{-3}$). Then, by comparing this emission measure with that of hot loops derived from SXT data, we are able to estimate the ratio between electron densities in hot and cool loops taking into account the effect of geometrical filling factors. This leads to the electron density in hot loops $7\times 10^{9}$ cm$^{-3}$. We also derive the temperature of hot X-ray loops ($\simeq 5\times 10^{6}$ K), which, together with the electron density, provides the initial values for solving the time-dependent energy balance equation. We obtain the cooling times which are compared to a typical growth-time of the whole loop system ($\sim $2000 sec). In the legs of cool \ha\ loops, we observe an excess of the emission measure which we attribute to the effect of Doppler brightening (due to large downflow velocities).
Continuation of the proposal: Physical conditions of the postflare loops on June 26, 1992 by B. Schmieder, P. Heinzel, J. E. Wiik , J. Lemen, B. Anwar and P. Kotr\v{c} and E. Hiei.
We would like to continue to work on the post flare loops of June 26 1992 by using all the orbits of SXT from 05 UT to 10:30 UT and to derive the emission measure variation versus time and versus a threshold of the intensity in the loops, like we did for one orbit in the accepted Solar Physics paper. In H alpha we have only 3 times but we could compare the 2 general behaviours of emission measure and deduce the evolution of the density of cold and hot plasma.
We would use deconvolved images to suppress the background as suggests Jim Lemen. The co authors are in good agreement to continue to collaborate.
Update 24-Mar-94
Following is the abstract of a paper to be presented at Cospar in July 1994, Symposium E2.2
RELATIONSHIP BETWEEN COOL AND HOT POST-FLARE LOOPS OF 26 JUNE 1992 DERIVED FROM OPTICAL AND X-RAY (SXT-YOHKOH) OBSERVATIONS
B. Schmieder (Observatoire de Paris, Section Meudon, 92195 Meudon, France)
P. Heinzel and P.Kotrc (Astronomical Institute, 25165 Ondrejov, Czech Republic)
J.E. Wiik (ESTEC, Holland )
E. Hiei (Meisei University, Tokyo)
J. Lemen (Lockheed Palo Alto Research Lab., Palo Alto, USA)
We have analyzed the physical conditions of the plasma in post-flare loops, both hot (SXT-data) and cool(optical ground-based data from Pic du Midi and Ondrejov), with special emphasis to dynamics and energy transport. By combining the \ha\ observations, optical spectra and SXT images we try to understand the relationship between the cool and hot plasma, the process of cooling the post-flare loops and the mechanism which maintains the long duration of these loops.
By using NLTE program developed in Ondrejov, plasma parameters are derived from MSDP and Ondrejov spectra: the electron density, the gas pressure and the temperature. We study particularly the soft X-ray irradiation of cool loops leading to a partial heating and ionization. MHD conditions in cool flare loops are studied and a free-fall model is checked.