From kusano@hiroshima-u.ac.jp Tue May 27 17:50:44 2003 Date: Tue, 13 May 2003 19:58:23 +0900 From: Kanya Kusano To: 'Pascal Demoulin' , 'mitch Berger' , 'Pablo Mininni' , 'Richard Canfield' , 'Alexander Nindos' , 'BC Low' , 'Jim Klimchuk' , 'Marcelo Lopez-Fuentes' , 'Sarah Gibson' , sakurai@solar.mtk.nao.ac.jp, 'Terry Forbes' , "'Brian T. Welsch'" , dana@mithra.physics.montana.edu, magara@mithra.physics.montana.edu, apevtsov@nso.edu, chae@cnu.ac.kr, haimin@sundog.caltech.edu, yjmoon@bbso.njit.edu Subject: RE: 2 new papers on magnetic helicity Dear Dr.Demoulin, Thanks for your notification on your new paper "Magnetic energy and helicity fluxes at the photospheric level". I enjoyed that, and basically agree with your opinion. However, I would like to tell you one comment on a part of this paper. You pointed out that, when the tracking method is used to derive the horizontal velocity, we should not add the vertical velocity onto the helicity and energy fluxes (eqs. 25 and 26 in your paper). This is true, and this effect was already taken into account in my method based on the induction equation (ApJ 2002, 577, 501). In your simple case (Fig.2 in your paper), the magnetic flux of each polarity across the photosphere is not changed. Therefore, if the local correlation tracking technique can perfectly work, the evolution of the magnetic poles (\partial B_n / \partial t) can be reproduced only by the electric field B_n x u_t. If so, the inverse problem of the induction equation gives us a solution that the vertical velocity is vanished everywhere (u_n=0). It means that the method based on the induction equation counts only the fluxes of the horizontal velocity automatically, even though the flux terms of the vertical velocity is calculated. It DOES NOT duplicate the flux parts included in the tracking velocity. In more general case where the magnetic flux changes, it is obvious that the vertical velocity should be included into the helicity and energy fluxes, since any horizontal motion cannot reproduce the change in total magnetic flux. On the other hand, if we use the tracking velocity and the vertical velocity observed by Doppler measurement, the fluxes may be duplicated. It is due to the fact that the velocity derived from the magnetic measurement u_t and the velocity from Doppler measurement v_n are NOT consistent each other. However, the induction equation can provide us the consistent velocity u_n with the tracking velocity u_t. Therefore, I do not think that your statement below eq.(26) "The use of v_n (as deduced from Doppler measurement or as proposed by Kusano et al., 2002) would only duplicate part of the fluxes already included in the tracking velocity \vec{u}." is appropriate. Please note that the method using the induction equation is different from the case of Doppler measurement. Anyway, I'm happy that I can discuss with you about this issue. Please send any comments and questions. Any information from you is welcomed! PS: My two papers on helicity issue entitled by "ANNIHILATION OF MAGNETIC HELICITY: A NEW MODEL OF SOLAR FLARE ONSET MECHANISM" and "MEASUREMENT OF MAGNETIC HELICITY FLUX INTO THE SOLAR CORONA" are now posted to Max Millennium E-Print Archive (http://solar.physics.montana.edu/cgi-bin/eprint/default_page.pl). Any comments from anybody to them are welcomed, too. Best my regards, Kanya -------------------------------------------------------- Kanya KUSANO, Graduate School of Advanced Sciences of Matter, Hiroshima University Higashi-Hiroshima, Hiroshima 739-8530, Japan Phone:[81] (824) 24-7016 fax: [81] (824) 24-7014 e-mail: kusano@hiroshima-u.ac.jp home page: http://plasma.sci.hiroshima-u.ac.jp/~kusano/ -------------------------------------------------------- -----Original Message----- From: Pascal Demoulin [mailto:Pascal.Demoulin@obspm.fr] Sent: Saturday, April 26, 2003 12:41 AM To: mitch Berger; Pablo Mininni; Richard Canfield; Alexander Nindos; BC Low; Jim Klimchuk; Marcelo Lopez-Fuentes; Sarah Gibson; sakurai@solar.mtk.nao.ac.jp; Terry Forbes; Brian T. Welsch; dana@mithra.physics.montana.edu; magara@mithra.physics.montana.edu; apevtsov@nso.edu; chae@cnu.ac.kr; haimin@sundog.caltech.edu; yjmoon@bbso.njit.edu; kusano@hiroshima-u.ac.jp Subject: 2 new papers on magnetic helicity Dear colleagues, Magnetic helicity has became a hot subject in these past years. Here are two new contributions to the subject. Your comments are well come !! Hoping this will continue to be a fast developing subject in the coming years ! They are posted on the Max Millenium E-print archive http://solar.physics.montana.edu/cgi-bin/eprint/index.pl But you can also got them directly on my web page http://www.solaire.obspm.fr/demoulin/newest.html Magnetic energy and helicity fluxes at the photospheric level Demoulin, P., Berger, M.A. , Solar Physics in press The source of coronal magnetic energy and helicity lies below the surface of the sun, probably in the convective zone dynamo. Measurements of magnetic and velocity fields can capture the fluxes of both magnetic energy and helicity crossing the photosphere. We point out the ambiguities which can occur when observations are used to compute these fluxes. In particular, we show that these fluxes should be computed only from the horizontal motions deduced by tracking the photospheric cut of magnetic flux tubes. These horizontal motions include the effect of both the emergence and the shearing motions what ever the magnetic configuration complexity is. We finally analyze the observational difficulties involved in deriving such fluxes, in particular the limitations of the correlation tracking methods. Obervations of magnetic helicity (review) van Driel-Gesztelyi L., Demoulin P., Mandrini C.H, Adv. Space Research, in press. The first observational signature of magnetic helicity in the solar atmosphere (sunspot whirls) was discovered 77 years ago. Since then, the existence of a cycle-invariant hemispheric helicity pattern has been firmly established through current helicity and morphological studies. During the last years, attempts were made to estimate/measure magnetic helicity from solar and interplanetary observations. Magnetic helicity (unlike current helicity) is one of the few global quantities that is conserved even in resistive magnetohydrodynamics (MHD) on a timescale less than the global diffusion timescale, thus magnetic helicity studies make it possible to trace helicity as it emerges from the sub-photospheric layers to the corona and then is ejected via coronal mass ejections (CMEs) into the interplanetary space reaching the Earth in a magnetic cloud. We give an overview of observational studies on the relative importance of different sources of magnetic helicity, i.e. whether photospheric plasma motions (photospheric differential rotation and localized shearing motions) or the twist of the emerging flux tubes created under the photosphere (presumably by the radial shear in the differential rotation in the tachocline) is the dominant helicity source. We examine the sources of errors present in these early results and try to judge how realistic they are. My best wishes, Pascal *====================================================================* Pascal Demoulin Phone: 33 1 45 07 78 16 Observatoire de Paris Fax: 33 1 45 07 79 59 section Meudon, LESIA, Bat. 14 http://www.solaire.obspm.fr/demoulin/ F-92195 Meudon Principal Cedex Pascal.Demoulin@obspm.fr France *====================================================================*