This paper consists of two parts. The first, resembling many
other SOHO contributions in this volume, reports on a recent campaign
in which SUMER was employed simultaneously with groundbased tele-
scopes. The campaign is described but results are not yet in hand.
The second part differs by proposing SUMER measurements and
analysis to be contributed by you. It calls attention to the FIP effect, a
puzzling outer-atmosphere element segregation that may have to do with
quiet-sun chromospheric dynamics. SUMER data, including yours, may
provide pertinent diagnostics

Rutten, R.J.

This paper consists of two parts. The first, resembling many

other SOHO contributions in this volume, reports on a recent campaign

in which SUMER was employed simultaneously with groundbased tele-

scopes. The campaign is described but results are not yet in hand.

The second part differs by proposing SUMER measurements and

analysis to be contributed by you. It calls attention to the FIP effect, a

puzzling outer-atmosphere element segregation that may have to do with

quiet-sun chromospheric dynamics. SUMER data, including yours, may

provide pertinent diagnostics

NARCIS 

Chromospheric Dynamics and the FIP Flip

Utrecht University Repository

B. Schmieder, J. C. Toro del Iniesta and M. Vazquez (Eds.): Advances in the Physics ofSunspots, Procs. First Adv. in Solar Physics Euroconf., Astron. Soc. Pac. Conf. Series 118,p. 298-302, 1997.Chromospheric Dynamics and the FIP FlipR.J. RuttenSterrekundig Instituut, Utrecht, The NetherlandsAbstract. This paper consists of two parts. The rst, resembling manyother SOHO contributions in this volume, reports on a recent campaignin which SUMER was employed simultaneously with groundbased tele-scopes. The campaign is described but results are not yet in hand.The second part diers by proposing SUMER measurements andanalysis to be contributed by you. It calls attention to the FIP eect, apuzzling outer-atmosphere element segregation that may have to do withquiet-sun chromospheric dynamics. SUMER data, including yours, mayprovide pertinent diagnostics.1. Dynamics of the quiet chromosphere and SUMER campaignOver the past years, studies of quiet-sun chromospheric dynamics have largelyconcentrated on the behavior of the Ca II H&K lines (see Rutten 1995 for areview). These strong lines portray a vivid distinction between chromosphericnetwork (NW) and internetwork (IN) regions (Lites et al. 1993). The NW isdelineated by fairly stable patches of bright emission that show modulationwith 5{15 min periodicities. It is not clear whether the modulation comes fromwaves or simply from erratic foot-point motions. There is no evidence for fasterwave motions. The IN areas show much more dynamic action, with three-minuteoscillations (periods 100{300 sec) occurring everywhere and sometimes brightlypeaking at K2Vand H2V. Carlsson & Stein (1994) have identied the formationof these H2Vand K2V\grains". They betray shock interference between upwardpropagating, steepening acoustic waves and backfalling matter from previousshock passages.The frontiers in quiet-sun dynamics lie higher up and deeper down, andin the connection between these regimes. For the NW patches, the persistentdowndrafts observed in the UV (Section 5.3 of Mariska 1992), the H mottleows (Tsiropoula et al. 1994), the shocks occurring in the Freiburg ux sheetsimulations (Steiner et al. 1996) and the long-neglected spicules (Beckers 1968)should be tied together. For the IN areas the roles of localized pistons thatdrive the three-minute oscillations (or even the ve-minute ones, see Rimmele1telescopeexit windowtrackerdichroicLC retarders248" x 195"255" x 171"171" x 125"Ca II K G band 430.5 nmH alpha166" x 130"Fe I 5250correlationFigure 1. Top: SVST setup. The Ca II K camera (0.3 nm band-width) and the G-band camera (1 nm) ran synchronously, with theG-band camera selecting the best two frame pairs every 20 seconds fordisk storage. The H and Fe I 525.0 nm cameras were used alterna-tively. The latter is part of a liquid crystal full-Stokes ltergraph thatis being developed at the SVST but was not yet operational duringthe SUMER run. Bottom: G{band frame taken on Sep 9 UT14:21:05.Demagnication by a factor two was used to cover the whole SUMERslit. Even so, Muller bright points and bright granule edges are visibleover the full 255  171 arcsec eld. The central part of the image isenlarged at the center of this print to illustrate its quality.2et al. 1995) and of the enigmatic internetwork elds (Keller et al. 1994, Liteset al. 1996) must be ascertained. Higher up, the IN regions contain C I jetsand 160 nm bright points that are connected to the acoustic shock dynamics(Hoekzema et al. 1997). It is not clear at what height and how magnetismaects the shocks.These issues are obvious motivation for SUMER data gathering. BruceLites (HAO) initiated and led a September campaign, rst setting up the Ad-vanced Stokes Polarimeter (ASP) at NSO/SP and than traveling to Goddardfor SUMER spectrometry while Tom Berger (Lockheed) moved from La Palmato Sacramento Peak and Dan Kiselman (Stockholm), Luc Rouppe van der Voort(Utrecht) and I took over at the SVST. We tried to use SUMER, ASP and theSVST simultaneously and cospatially during 14:00{17:30 UT on September 1{10, running into the usual problems of pointing alignment and bad weather orbad seeing at ground level.SUMER was used mostly at disk center with the slit set to follow rotation,selecting the  = 131 and 103 nm wavelength regions. The ASP slit was setto scan around the (alleged) SUMER slit position. At the SVST, we obtainedltergrams with the setup shown in Fig. 1. The best day at la Palma was Sep 9,when the seeing was often good (Fig. 1). These data should permit correlationof granular behavior in the photosphere with the chromospheric dynamics seenin Ca II K and by SUMER.2. The FIP ip and SUMERThe FIP eect is a well-established deviation of the coronal and solar windabundances from the composition of the solar photosphere (see reviews by Meyer1985, 1991, 1993). A similar deviation occurs in galactic cosmic rays and in solarenergetic particles. In the slow-speed solar wind and the underlying closed-eldregions of the corona, elements with First Ionization Potential (FIP) below 10 eV(Mg, Fe, Si) are overabundant with respect to high-FIP elements (N, O, Ar, Ne,He and possibly C) by about a factor four. Figure 2 displays this ip.The segregation must obviously occur in circumstances where dierence inFIP makes a dierence, so well before the high-FIP atoms loose their outer elec-trons and are accelerated into the solar wind. Therefore, the outer-atmospherelow-FIP excess must be due to some neutral-ion separation process in the chro-mosphere where hydrogen and C, N and O are still predominantly neutral.In this regime, the charged low-FIP particles (which are predominantly once-ionized even throughout the photosphere) are presumably line-tied to magneticelds while the high-FIP neutrals may ow or diuse transversely across eldlines. The segregation must be sensitive to the topology of the magnetic eldsince it is much smaller or absent in the fast wind streams that emanate fromthe open-eld regions.There are various FIP-eect scenarios in the literature that all assume line-tying of charged particles (with the exception of the implausible meteorite sce-nario of Lemaire 1990). For example, Vauclair & Meyer (1985) let neutral atomsdiuse downwards out of horizontal magnetic eld, Ip & Axford (1991) andVauclair (1996) propose that an upward sweeping horizontal uxtube collectscharged particles, while Von Steiger & Geiss (1989) and Marsch et al. (1995)3Figure 2. The FIP eect. The quantity f measures elemental abun-dance normalized by the photospheric value, on a relative scale withlog f = 0 assigned to oxygen. Bars (SW) are from in-situ slow solarwind sampling, rectangles (SEP) for solar energetic particles. The dotsfollow from a diusion model. From Von Steiger & Geiss (1989).use UV radiation from above to ionize the neutral low chromosphere at somecharacteristic depth, letting the remaining neutrals diuse horizontally out of anarrow vertical uxtube (rst paper) or the ions dierentially upward along avertical eld (second paper).It seems to me that the IN shock dynamics represent a viable alternativesince the shocks observed in Ca II H&K and in HRTS C I jets represent thelargest-amplitude motions in the low quiet-sun chromosphere and are ubiqui-tously present all over the quiet sun. In closed eld regions, the upward prop-agating shocks penetrate into a rather low-lying canopy. At the height whereneutrals and ions may start to uncouple (as set by the collision frequency), suchlow-lying canopy elds may be strong enough to dampen the shocks and in par-ticular, to inhibit the post-shock ballistic backfall which is the major dynamicalphenomenon in the Carlsson{Stein simulation. Thus, the canopy eld may actas a sieve through which high-FIP neutrals drop back down easier than low-FIPions. The trapped ions may then preferentially take part in the mottle owsalong the eld towards the network locations, and eventually end up in theouter atmosphere when bril loops expand and erupt.How might SUMER diagnose such FIP segregation? I suspect that low-chromosphere Dopplershift signatures of the network and internetwork dynamicsprovide a clearer FIP diagnostic than line intensities. Interpretation of the lattertends to be questionable even for apparently optically thin conditions (Schrijveret al. 1994), whereas line formation in the hydrogen-neutral regime where theFIP fractionation takes place is optically thick and very complex for most ifnot all lines of interest. Thus, dynamical prole resolution and interpretation isrequired, rather than simple time-averaging of integrated line intensities. Aver-aging will be required to bring out low-FIP versus high-FIP dynamics dierences,4but such averaging must be done over resolved states of dynamic behavior. InSUMER setup terms, this means that a dynamically-oriented search for FIPfractionation imposes quite similar constraints as the various SUMER chromo-spheric dynamics programs. High time resolution and full spatial resolution arerequired to resolve the dynamical state of the chromosphere. Obviously, bothlow-FIP and high-FIP lines must be measured, preferably with dierence in for-mation characteristics (height; thick/thin if feasible). On the other hand, a FIPsearch requires very large datasets, covering much space and much time to gainsucient statistics in sampling the various dynamical processes. Finally, sucha search should also enable dierentiation between closed-eld and open-eldregions of the corona.The message is that data from many programs will have to be combined insuch a search. My request to you is to make sure that your line selection in anySUMER dynamics programs aims to include FIP dierence.Acknowledgments. I thank Goran Scharmer, Rolf Kever, Goran Hosinskyand Dick Shine for much support at the SVST. Rudi von Steiger, Bert van denOord and Benno Hessel took part in formulating the FIP suggestion.ReferencesBeckers, J. M. 1968, Solar Phys., 3, 367Carlsson, M., Stein, R. F. 1994, in M. Carlsson (ed.), Chromospheric Dynamics,Proc. Miniworkshop, Inst. Theor. Astrophys., Oslo, p. 47Hoekzema, N. M., Rutten, R. J., Cook, J. W. 1997, Astrophys. J., in pressIp, W. H., Axford, W. I. 1991, Advances in Space Research, 11, 247Keller, C. U., Deubner, F. L., Egger, U., Fleck, B., Povel, H. P. 1994, A&A,286, 626Lemaire, J. 1990, ApJ, 360, 288Lites, B. W., Leka, K. D., Skumanich, A., Martinez Pillet, V., Shimizu, T. 1996,ApJ, 460, 1019Lites, B. W., Rutten, R. J., Kalkofen, W. 1993, Astrophys. J., 414, 345Mariska, J. T. 1992, The Solar Transition Region, Cambridge Univ. Press,Cambridge UKMarsch, E., Von Steiger, R., Bochsler, P. 1995, A&A, 301, 261Meyer, J. P. 1985, ApJS, 57, 173Meyer, J.-P. 1991, Advances in Space Research, 11, 269Meyer, J.-P. 1993, Advances in Space Research, 13, 377Rimmele, T. R., Goode, P. R., Harold, E., Stebbins, R. T. 1995, ApJ, 444, L119Rutten, R. J. 1995, in J. T. Hoeksema, V. Domingo, B. Fleck, B. Battrick(eds.), Helioseismology, Proc. Fourth SOHOWorkshop, ESA SP{376 Vol.1, ESA Publ. Div., ESTEC, Noordwijk, p. 151Schrijver, C. J., Van Der Oord, G. H. J., Mewe, R. 1994, A&A, 289, L23Steiner, O., Knolker, M., Schussler, M. 1996, in V. Hansteen (ed.), Proceedingsof the MINI-Workshop on Solar Magnetic Fields, Institute of TheoreticalAstrophysics, University of Oslo, Oslo, in pressTsiropoula, G., Alissandrakis, C. E., Schmieder, B. 1994, A&A, 290, 285Vauclair, S. 1996, A&A, 308, 228Vauclair, S., Meyer, J. P. 1985, in NASA Goddard Space Flight Center 19thIntern. Cosmic Ray Conf., Vol. 4, p. 233Von Steiger, R., Geiss, J. 1989, A&A, 225, 2225

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