Science JOPs: JOP 22 (may 1999, updated version) Title: Network study: dynamics, evolution and lifetime Lead Person: P. Lemaire Authors: K.P. Dere, F. Auchere (LASCO/EIT), A. Fludra (CDS), P. Lemaire (SUMER), MDI and TRACE participation SOHO instruments involved: CDS, EIT, MDI, SUMER, TRACE Collaborating GBO: (to be established) spectrographs, magnetographs, high resolution filters (including MSDP),THEMIS Collaborating S/C: TRACE Campaign: yes Last update: May 10, 1999 First idea proposed: SPWG January 1995 Object: quiet Sun and coronal holes. NETWORK STUDY: DYNAMICS, EVOLUTION and LIFETIME (JOP 22) 1. - Scientific Objective The primary scientific goals of the observing program are: - the study of the short term (hours) and long term (days) dynamics of the network in quiet and coronal holes areas, - the characteristics of the atmospheric parameters associated with supergranular cells and their network boundaries ( 3-D morphology, temperature, density and velocity along the lifetime of structures) in quiet Sun and in coronal holes. - the contribution of the network to the energy budget of the solar atmosphere from the chromosphere to the corona and its variation along the rising activity cycle. 2. - Scientific rationale The network is the backbone of the upper part of the quiet ( and coronal hole) atmosphere from the chromosphere to the base of the corona. It encloses supergranular cells and is the result of the supergranular flow pattern which sweeps magnetic elements to the boundaries where the magnetic flux becomes concentrated. The supergranular cells are produced by the emergence of convective flux generated in the He II convection zone: the lifetime (24 - 80 hours, Liu et al. A. & A. 283, 215, 1994), the horizontal and vertical flows (at photospheric level) may be explained by a coupling of rotational oscillatio n and convection (Wolff, Ap.J. 443,423,1995). The total area covered by networks and cells on the solar surface is greater than 85% in very active Sun and than 95% in activity minimum at chromospheric level. During the lifetime of a cell, the network, made of magnetic elements, is completely recycled. During a solar cycle the size of the supergranular cells varies and the contrast of the network is related to the activity level. All these observations bring growing evidence that the supergranular cell/network structuration is a process that may be an important key to understand the heating of the corona through the channeling of the magnetic flux in the network. All current theories of coronal heating start from the premise that the photospheric motions perform work on the footpoints of coronal loops.This energy is then transmitted into the corona where it is dissipated. Some theories require that the motions induce a twist on the coronal loops while others only require a stochastic rearrangement of the field lines. To date, it has not been possible to study the photospheric motions, the magnetic field footpoints and the coronal loops. These are key observations for understanding the coronal heating mechanism and are the goal of this JOP The knowledge of the network parameters and the role played by the magnetic field are needed - to estimate the respective contribution of heating, conduction, radiative and mechanical energy dissipation in the modeling of the transition zone and the corona, - to improve our understanding of the differenciation between quiet Sun and coronal hole as a function of height above the solar surface. The instrumentation on SOHO provides a unique opportunity to make a critical set of observations that have not been possible in the past. We propose to study the dynamics of network in 2 scales: - a small scale using the highest resolution available to follow the evolution of individual magnetic elements during few hours from the photosphere to the corona, - a large scale covering about 30 supergranular cells to determine the global evolution of the network during several days along the full height of the atmosphere. - a full Sun periodic coverage to follow the variation of the relative contribution of network/cell to the total energy budget. To bring significant informations this study must be as continuous as possible during the full program (several days) and be made on three different targets: quiet Sun, coronal hole and edge of coronal hole. The set of observations must be repeated at least every 6 months to scan the rising cycle of solar activity. During the 6 months intervals between detailed studies, the continuity of statistical observation of the network/cell contribution must be performed by full Sun images in the chromosphere/transition region. 3. - Observables Photosphere - low chromosphere (MDI and GBO contributions): - supergranular cells/network morphology (intensity distribution) - velocity field (horizontal and vertical) - magnetic field Chromosphere to corona (EIT, SUMER, CDS): - morphology (intensity distribution) in selecting lines spanning the 6000 K - 1.5 10^6 K temperature range - velocity field (derived from line shift and line broadening) 4. - Pointing and target selection It is preferable to observe the network when it is near Sun center, i.e beginning the observation few days (2 - 3 days) before meridian crossing. A typical length of observation must be 4 - 5 days with minimal interruptions. The target selection is also constrained by the need to have the MDI high resolution field at least during the 8 hours real time contact. That constraint is weak to observe quiet Sun network, but may lead to a strong priority (within SOHO) to observe coronal hole (center and border) network. The small field selected to be study with high resolution must be near the middle of the large field used to provide the long term evolution of the network. To provide a better view on detailed and global evolutions it is suggested to interlace observations of small and large fields. 5. - Observations ============================================================================== Old version =============================================================================== SUMER The SUMER observation will be continuous during 18 hours a day to leave place to the Full Sun synoptic image (that gives full Sun distribution of network) and to the 30 min high rate telemetry for EIT. The lines of interest are selected to cover chromosphere to corona temperature range, to be within 2 detector formats (42A bandpass in 1rst order) and to be bright enough to have short integration time. So we suggest HI Ly beta (1025A) and OVI (1032A,1037A) for one format and Mg X (x2) (1219.6A, C III (1247A), N V (1243A), O V(x2) (1259A) and S II(1250A) for the second format. To obtain the wavelength reference in every line a low chromospheric line must be included in the measurements and the final wavelength optimisation for low ionized elemnts will be done after checking on the first solar spectra recorded by SUMER. Several types of programs can be accomplished and in the following we provide 2 examples. A) First program made to have a better statistic in number of cells/networks First sequence: Wide area Initial pointing: Quiet (coronal hole,..) area near disk center slit: 1" x 300" scan area 120" x 300" step size .76" x 2 running mean (solar compensation) dwell time 2 sec (first set of wavelengths) 8 sec (second set of wavelengths) duration of scan 150 sec (1) 680 sec (2) number of scans 2 for set (1)(one direction and reverse) 1 for set (2) number of scan mirror settings 2 repointing no total duration 990 sec line selection (1) L beta (1025A), O VI (1032-1037A), CII (2) Mg X(x2)(1219.6A), C III(1247A), N V(1243A) O V(x2) (1259A), S II (1250.5A), C I (1253.5A) Binning 1 Compression 5 moments (1) 2 moments/line (2) Second sequence: Small area Initial pointing network part at the center of the wide field Slit 1" x 300" Scan area 15" x 300" (solar rotation compensation) step size 0.76" Dwell time 2 sec (1) 20 sec (2) Duration of scan 40 sec (1) 400 sec (2) Number of scans 5 (1)+(2) Number of mirror settings 2 x 5 Repointing None Total duration 2600 sec Line selection (1) L beta (1025A), O VI (1032-1037A), CII (2) Mg X(x2)(1219.6A),C III(1247A), N V (1238- 1243A),O V(x2)(1259A),S II(1250.5A),C I(1253.5A) Binning 1 Compression 5 moments (1) 2 moments/line (2) First and second sequences (1 hour) are repeated 18 times per day (+5 h 15 min for Full Sun imaging + 30 min for EIT high rate telemetry). This daily program is repeated during 5 days. B) Second program to obtain accurate profiles in few supergranular cells/ networks First sequence: Wide area Initial pointing: Quiet (coronal hole,..) area near disk center slit: 1" x 120" scan area 120" x 120" step size .76" x 2 running mean (solar compensation) dwell time 4 sec (first set of wavelengths) 8 sec (second set of wavelengths) duration of scan 300 sec (1) 680 sec (2) number of scans 1 for set (1) 1 for set (2) number of scan mirror settings 2 repointing no total duration 990 sec line selection (1) L beta (1025A), O VI (1032-1037A), CII (2) Mg X(x2)(1219.6A), C III(1247A), N V(1243A) O V(x2) (1259A), S II (1250.5A), C I (1253.5A) Binning 1 Compression 5 moments (1) 2 moments/line (2) Second sequence: Small area Initial pointing network part at the center of the wide field Slit 1" x 120" Scan area 15" x 120" (solar rotation compensation) step size 0.76" Dwell time 2 sec (1) 20 sec (2) Duration of scan 160 sec (1) 400 sec (2) Number of scans 4 (1)+(2) Number of mirror settings 2 x 4 Repointing None Total duration 2400 sec Line selection (1) L beta (1025A), O VI (1032-1037A), CII (2) Mg X(x2)(1219.6A), C III(1247A), N V(1238- 1243A),O V(x2)(1259A),S II(1250.5A),C I(1253.5A) Binning 1 Compression Quasi-log min_max Format 25 x 120 (Full line profile) Third sequence: Small area at high time resolution (to replace time-to-time the second sequence) Initial pointing network edge at the center of the field Slit 1" x 120" Scan area 15" x 120" (solar rotation compensation) Step size 0.76" Dwell time 1 sec (1) 2 sec (2) Duration of scan 20 sec (1) 40 sec (2) Number of scans 100 (1) + 50 (2) Number of mirror settings 2 Total duration ~ 4000 sec Line selection (1) O VI (1032A) (2) Si III (1206A), Si II (1197) Binning 1 Compression Quasi-log min_max Format 50 x 24 First and second sequences (1 hour) are repeated 18 times per day (+5 h 15 min for Full Sun imaging + 30 min for EIT high rate telemetry). This daily program is repeated during 5 days. Following is a Preliminary CDS contribution. From: A. Fludra ----------------------------------------------------- CDS Line list for the Network JOP: Normal Incidence (NIS): short exposure (20 s) Ion Wavelength QS cnts/s Tpeak (A) (per 2''x 2'') (K) He I 584.33 32.9 2.0e4 He II (2) 303.78 24.7 5.0e4 O IV 554.52 27.3 2.0e5 O V 629.73 16.3 2.0e5 Mg IX 368.06 23.8 1.0e6 Normal Incidence: long exposure (200 - 300 s): As above, plus the following lines: O III 599.59 1.9 9.0e4 Ne V 569.20 0.35 3.0e5 Ne V 572.20 0.52 3.0e5 Ne VI 558.89 0.52 4.0e5 Ne VI 562.83 0.36 4.0e5 Mg VI 349.13 1.0 4.0e5 Ca X 557.76 1.0 6.3e5 Ca X 574.00 0.46 6.3e5 Si VIII 316.22 1.4 7.9e5 Si VIII 319.83 2.0 7.9e5 Si IX 341.95 2.4 1.0e6 Si IX 345.13 4.4 1.0e6 Si X 347.40 7.0 1.0e6 Grazing Incidence: Required long exposure (200 - 300 s) Ion Wavelength QS cnts/s Tpeak (A) (per 2''x 2'') (K) He II 303.78 149.3 5.0e4 O II 718.53 0.7 6.3e4 N III 685.83 1.1 8.0e4 O III 702.98 2.7 9.0e4 N IV 765.14 2.4 1.0e5 O V 760.40 0.9 2.0e5 Mg VI 399.20 0.7 4.0e5 Mg VI 400.68 0.9 4.0e5 Ne VI 399.83 0.7 4.0e5 Ne VI 401.14 2.8 4.0e5 Ne VII 465.22 4.4 5.0e5 Ne VIII 770.40 2.8 6.0e5 Ne VIII 780.30 1.4 6.0e5 Mg VII 434.93 1.0 6.3e5 S VIII 202.61 0.4 7.9e5 S VIII 202.61 0.4 7.9e5 Na VIII 411.16 1.0 9.0e5 Mg VIII 436.73 1.5 9.0e5 Example of CDS Study Details (Bright Lines option) wide area small area Spectrometer: Normal Incidence Normal Incidence Slit: 2 x 240 arcsec 2 x 240 arcsec Raster Area: 120'' x 240'' 16'' x 240'' Step (DX) 2 arcsec 2 arcsec Raster Locations: 60 8 Exposure Time: 20 seconds 20 sec Duration of raster: 20 minutes 160 sec Number of rasters: 3 15 Total duration: 60 minutes 40 minutes Line selection: He I 584.33 A, He II (2) 607.56, O IV 554.52, O V 629.73, Mg IX 368.06 A Bins Across Line: 15 Telemetry/Compression: truncate to 12 bits Pointing: centre of the SUMER area Flags: Solar Feature Tracking: yes ----------------------------------------------------- EIT (2.6 arc-sec pixels): Exposure Times: 170 A (Fe IX/X) 10s 195 A (Fe XII) 20s 284 A (Fe XV) 300s 304 A (He II) 100s FOV: 416 arc-sec square ~7 arc-min square to match MDI 5x5 32 pixel blocks Repetition rate: 4 images every 8 min. In later runs, eliminating the Fe XV channel can make this faster Total duration: 24 hr. ---------------------------------------------------------------- MDI (High Resolution Mode / 0.625 arc-sec pixels): FOV: 7 arc-min square Data: continuum image doppler image magnetograms Repetition rate: 1 set per minute Total duration: 8 hours during real time downlink Full disk magnetograms to fill in rest of 24 hour program ========================================================================== New version for may 1999 Observation near Sun center SUMER If B detector use of the 750-790A wavelength range (O IV,O V,N IV,S V, Ne VIII) Wavelength and slit (1 x 300") are setted for the whole program - first establishing the wavelength scale by pointing off-limb, using the solar scattered light - a small raster (120"x300") in O IV,O V,NIV and Ne VIII to cover part of the field which will be provide by the solar rotation - rotation of the Sun provides the scanning. A set of lines every 90 seconds - a small raster, same size as previous, offsetted to cover part of the field provided by the solar rotation If A detector use of the 1540-1580A wavelength range (O IV,CIV,S V,Ne VIII) - rotation of the Sun provides the scanning. A set of lines every 90 seconds Total duration 22hr 30 mininimum CDS High cadence variability in He I, O IV, O V, Ne VI - slit 4"x240" - sit and stare 15-s cadence - narrow raster (30"x240") with 2 min cadence - same raster with 2"x240" slit with 4 min cadence EIT A He 304A subfield (8'x8')each one or two hours. MDI Few magnetograms TRACE Selection of Lyman alpha images will be helpful GBO observations Ca II lines (H, K or Infrared triplet) Magnetic field