JOP163 Internetwork and Network Oscillations: The influence of magnetic fields on atmospheric dynamics Received: January 23, 2003 Short title: Internetwork/Network Oscillations Contributors: D. Banerjee - Centre for Plasma Astrophysics, K.U.Leuven E.O'Shea - Instituto de Astrofisica de Canarias Luc Dame - Service d'Ae'ronomie du CNRS S.S. Hasan - Indian Institute of Astrophysics W. Kalkofen - Harvard-Smithsonian Center for Astrophysics Participating instruments: CDS, MDI and TRACE Scientific Objective: --------------------- The primary objective of this observing program is to study the dynamics of the quiet chromosphere and to delineate the role of magnetic fields on internetwork and network oscillations. MDI and TRACE photospheric and UV imaging of TRACE are requested to acquire simultaneous high temporal and spatial coverage along with the spectroscopic data from CDS. Scientific Justification: ------------------------ Previous JOP programs (13,20,22, 46, 72 & 78) have detected oscillations at different heights in the quiet solar atmosphere and have attempted to understand the physical nature of these oscillations. It has been shown that the behaviour of various spectral lines at different layers in the atmosphere are significantly different in the network and inter-network and this difference has been attributed to the presence of magnetic field. However, the origin of these oscillations and the role of magnetic fields on the Ca K2v bright grains within the inter-network is still not clear. Thus, one must continue to turn to new observations for further insight into these regions of the solar atmosphere. MDI magnetograms with the 2D CDS rasters will provide exact co-alignment of different regions and will give indications of the possible influence of magnetic fields. Detailed analysis will require numerical simulations of gas dynamics in flux tubes. Observations have firmly established the presence of oscillations in the solar atmosphere. The internetwork medium is dominated with oscillations having power in the 5-7 mHz range, which can essentially be regarded as acoustic waves. Significant progress has been made recently in modeling wave propagation in the non-magnetic medium and applying these calculations to interpreting the properties of K2v grains. However, the question regarding their generation and why they occur at specific locations in the cell interior is still unclear. Calcium K and H grains correlate with internetwork magnetic field concentrations, as suggested by Sivaraman and Livingston (1982) (see also Kneer and von Uexkuell 1993, Nindos and Zirin 1998, Lin and Rimmele 1999, Sivaraman et al. 2000), which led Kalkofen (1996) (see also Steiner et al. 1998) to propose that the oscillations are generated due to collisions between granules and flux tubes. For fields of a few hundred Gauss, this leads preferentially to the excitation of a longitudinal MHD mode having a cutoff frequency that is almost identical to the usual acoustic cutoff frequency. However, using the ASP with high sensitivity, Lites et al. (1999) did not detect a correlation between fields and grains (see also Worden et al. 1999). An alternative scenario is that the localized pistons are driven by turbulent convection. Transient ``acoustic events'' observed by Rimmele et al. (1995) (see also Restaino et al. 1993, Roudier et al. 1997, Hoekzema et al. 1998, Goode et al. 1998) are perhaps excited in the sub-photosphere and above in the overshoot layer by collapsing granules, which generate gravity modified acoustic waves with periods close to the 3-min. cutoff period (e.g. Skartlien et al. 2000). Clearly, more observational work is required to settle this question. The dynamics of the magnetic network, on the other hand, is dominated by low frequency waves with periods in the 4-15 min. range, which can be interpreted as transverse MHD waves, generated in thin flux tubes by granular buffeting. Through nonlinear effects, these modes generate longitudinal MHD waves, that form shocks and dissipate in the low to middle chromosphere (e.g. Hasan et al. 2003; see also Zhugzhda et al. 1995 ). This description appears to be reasonable up to heights where the magnetic elements are distinct (roughly up to heights of about 1 Mm). Higher up in the chromosphere the situation becomes more complex due to the merging of different flux tubes. Observations of oscillations in the magnetic chromosphere could provide vital information that lead to a better understanding of their nature as well as providing useful clues to theoretical interpretation. Operation: ---------- MDI: High resolution I_cont, V_dopp, B_long measurements in the limited FOV around the disk center. Contact: L. Dame (luc.dame@aerov.jussieu.fr) ------------------------------------------- Operational Sequence:CDS Temporal sequence: Initial Pointing Quiet Sun disk centre or close to it, to match MDI HR field. Spectrometer NIS Slit 4 x 240 arcsec Exposure Time 45s Number of Repeats/Rasters 225 Total Duration ~11,250s (cadence of ~50s) Line Selection He I 584 log 4.5 O III 599 log 5.0 Ne IV 543 log 5.2 O V 629 log 5.4 Ne VI 562 log 5.6 Ca X / Ne VI log 5.8 / 5.6 (centre window at wavelength in between that of Ca X and Ne VI, i.e. ~558.180) Mg IX 368 log 6.0 Mg X 624 log 6.1 Spectral window width 35 pixels Binning No binning along the slit Raster sequence: Initial Pointing Quiet Sun disk centre or close to it, to match MDI HR field, and pointing of quiet Sun time series observations. Spectrometer NIS Slit 4 x 240 arcsec Exposure Time 35s (cadence of ~40s) Number of Raster Steps 60 (to build up a 240x240 raster) Total Duration ~2400 s Line Selection He I 584 (log 4.5) O III 599 (log 5.0) Ne IV (log 5.2) O V (log 5.4) Ne VI 562 (log 5.6) Mg X 624 (log 6.1) Spectral window width 30 pixels Contact: D. Banerjee (dipu@wis.kuleuven.ac.be) ----------------------------------------------------------------------------- TRACE: Wavelengths: CIV series (1550,1600,1700) in 15s cadence Frame: 512x512 pixels centered subfield read, no binning. Compression: Lossless. Exposure: 10s (compatible with 15s cadence) Name of program: similar to TDT.trnotsofast (program used for JOP097 of SOHO in 2000) but with a field 512x512. Modification: NO wl images interleaved. Sequence: to be run for 3h every morning (+1h for emptying the memory) (to match the time of the CDS runs, with the pointing being taken from the CDS observations, disk centre quiet Sun regions) Contact: L. Dame (luc.dame@aerov.jussieu.fr). ----------------------------------------------------------------------------- Proposed observation dates: The dates are completely flexible, depending on the target opportunity, quiet sun disk center is necessary. 7-10 days of observations requested, need not be consecutive. ------------------------------------------------------------------ References: Goode, P.R., et al. 1998, ApJ, 495, L27 Hasan. S.S. et al. 2003, ApJ, (in press) Hoekzema.N.M., Rutten, R.J., 1998, A&A, 329, 725 Kalkofen, W., 1996, ApJL, 468, L69 Kneer, F., von Uexkull, M., A&A, 1993, 274, 584 Lin, H., Rimmele, T., 1999, ApJ, 514, 448 Lites, B.W., Rutten, R. J., Berger, T. E., 1999, ApJ, 517, 1013 Nindos, A., Zirin, H., 1998, Solar Physics, 179, 253 Rimmele, T., et al. 1995, ApJ, 444, L119 Restaino, S.R., et al. 1993, ApJ, 408, L57 Roudier. T., et al. 1997, A&A, 20, 605 Sivaraman, K.R., et al., 2000, A&A, 363, 279 Sivaraman, K. R., Livingston, W. 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