Joint Observing Program #40 Transition Region Network Thickness updated: April 30, 1999 Participants : Jean-Claude Vial (SUMER), K. Bocchialini (SUMER), Richard Harrison (CDS) Ted Tarbell (MDI), J.-P. Delaboudiniere (EIT) S. Patsourakos, A. Fludra (CDS), P. Lemaire (SUMER) Scientific Justification : The chromospheric and transition region network is believed to be the basic channel of energy and momentum that heats the corona and accelerates the solar wind. While at spatial scales of one supergranular cell the network appears to be more or less homogeneous and steady, at smaller spatial scales it possesses a finer structure as well a dynamic character (e.g. Dere et al., 1987, Dowdy et al., 1986). For establishing the steady-state energy and momentum balance it is of vital importance to have a precise knowledge of the network boundaries area (as well its temperature variation) over which the relative fluxes should be integrated. Recent results of CDS data analysis (Patsourakos et al., to appear in ApJ's September issue) are in a good agreement with the funnel-shaped concept of the transition region (e.g. Gabriel, 1976) for temperatures above 10^5.4 K. However, there still exist a number of problems to be addressed: (1) what is the filling factor of the network and how it varies with temperature (or in other words what is the importance of the fine structure for the funnels ?) (2) what is the structure of the lower transition region (funnels versus small loops) ? (3) how the magnetic field structure in the photosphere relates with the the overlying network ? (4) do minute-scale temporal changes in the network really matter when studying the network at large spatial scales ? (5) does it exist a difference for all the previous points between quiet Sun and Coronal holes ? Methodology : The lower temperature region could be better viewed with high spatial resolution instruments (SUMER, TRACE) while filling factors at transition region and coronal temperatures could be obtained thanks to CDS diagnostic capabilities. MDI high resolution magnetograms will give access to the underlying magnetic field pattern. Finally, EIT, TRACE and MDI could follow the network evolution at spatial scales of several supergranular cells with a cadence of several minutes something not possible with the spectrometers that are obliged to raster inorder to image a large area on the Sun. The main target of this JOP is a quiet Sun region as well a Coronal hole (preferably on the disk -if any for the time of the observations- inorder to have a radial line of sight). Instrumental Contribution : A/ SUMER : (i) spectral window : 750-790 A spectral lines : ion wavelength(A) T(K) OV 760 5.4 NIV 765 5.2 Ne VIII 770 5.8 SV 787 5.2 OIV 791 5.2 slit : 2 (1"x300") exp time : 72 s format : 8 step : 1" scanned field of view : 120"x300" in raster mode duration : 2.8 hr (ii) spectral window : 1230-1270 A main spectral lines : ion wavelength(A) T(K) N V 1238 10^5.3 Mg X 625*2 10^6.0 O V 630*2 10^5.4 slit : 2 (1"x300") exp time : 6 minutes to allow the faint Mg X line to emerge in the coronal hole spectra. (full detector readout) format : 2 scanned field of view : 50"300" in sit and stare mode duration : 5 hr (note: before and after each part a 5 minutes reference spectrum with the slit cutting the solar limb (to provide a wavelength calibration) will be taken) B/ CDS : study name LARGEBP2 (updated version - new line list) slit : 2"x240" scan are : 240"x240" step size : 2" step number : 120 exposure time : 45 s total duration : 4hr 40 min repetition rate: 1 C/ MDI : Full-disk 1-minute magnetograms and doppler images that MDI is currently obtaining. D/ EIT : Synoptic images (obtained at full resolution every 6 hours in all the 4 EIT bands) and half-resolution "CME watch" images every ~ 12 minutes (Fe XII). E/ TRACE (proposed sequence): Full-fov images (256"x256") in the Fe IX/X, Ly a and CIV channels with 1 minute cadence for 3-4 hours. References : Dere, K. P., Bartoe, J.-D. F., Brueckner, G. E., Cook, J. W., and Socker, D. G., 1987, Solar Phys, 114, 223 Dowdy, J. F., JR., Rabin, D., and Moore, R., L., 1986, Solar Phys, 105, 35 Gabriel, A. H. 1976, Phil. Trans. Roy. Lond. A, 28l, 575 Patsourakos S., Vial, J.-C., Gabriel, A.-H., and Bellamine, N. ApJ, 1999, accepted :::::::::::::::::::::::::::::::::::::::::::::: Patsourakos Spyridwn Institut d'Astrophysique Spatiale (I.A.S.) Universite Paris XI 91 405 ORSAY Cedex France tel: 01 69 85 87 41 fax: 01 69 85 87 01 ::::::::::::::::::::::::::::::::::::::::::::::