JOP080 TITLE : High-time resolution imaging study of coronal and transition region dynamics (EIT shutterless-mode campaign). AUTHORS : F. Clette (EIT, Leader), fred@oma.be K. Muglach (SUMER), muglach@so.estec.esa.nl A. Fludra (CDS), fludra@cds8.nascom.nasa.gov D. Mc Kenzie (YOHKOH/SXT), mckenzie@sxt4.physics.montana.edu C. Kankelborg (TRACE), kankel@physics.montana.edu C. De Forest (MDI), zowie@urania.nascom.nasa.gov VERSION : 1 (1998/03/18) OUTLINE : This program focuses on the study of bright structures (active region loops, bright points) with the highest possible time resolution (approx. 15 sec) and the wide spatial coverage provided by imaging data (EIT, TRACE, SXT, MDI). This high time resolution imaging study thus complements other JOPs which are also exploring small-scale periodic and intermittent phenomena (45, 59, 75) but preserve the spatial resolution by reducing the time cadence or the size of the field of view. The combination of the EIT and TRACE imagers would allow also to produce simultaneous images in two complementary wavelengths, which is impossible to achieve with either of these experiments due to mechanical limitations. SCIENTIFIC JUSTIFICATION Theoretical considerations as well as recent observations from SOHO and other spacecrafts tend to indicate that physical mechanisms leading to the ultimate energy deposition in the corona are acting over spatial and temporal scales that are well below the resolution provided by current instruments (Zirker, 1993). Although observations from NIXT, SUMER and now from TRACE, give access to spatial scales of the order of 1 arcsec, i.e. 1000 km, the relevant spatial scales are probably below 1 km. On the other hand, temporal resolutions of the order of a few seconds can be achieved and fall in the typical range of timescales where mechanisms like reconnection, turbulence and wave propagation are taking place. For instance, according to models that relate magnetic loop oscillations to their typical size, the expected frequencies range from 100 mHz down to only 10 millihertz (Poeds & Boynton 1996, Hansteen 1997). A search of such oscillations based on YOHKOH image sequences hints at the existence of such oscillations in large-size AR loops (Mc Kenzie & Mullan 1997). Simulations of impulsive energy release in magnetic loops show that the resulting temperature can display display abrupt local changes over less than a minute, in response to even shorter energy injections (Walsh et al. 1997). Moreover, extensive statistics of quiet Sun transients in the corona and the transition regions detected by EIT recently showed the existence of a continuous distribution over energy and duration with a power-law increase towards lower values down to the 1 min time-resolution available at the time (Berghmans & Clette 1998). OBSERVING PROGRAM Based on the experience acquired during an earlier observing campaign (Nb. 1550), we propose to explore the shortest timescales accessible with current instruments, by combining several imaging instruments, which provide the advantage of a wide field of view. To achieve this, we take advantage of the shutterless exposure mode of EIT, that was tested and applied successfully during a first campaign in May 1997, and which allows to reach cadences of the order of 15 seconds. For this study, we want in particular to take full advantage of the 3 x 4 arcmin size of the subimages, which allows a good statistics of many local events as well as a full coverage of an extended structure (e.g. one loop with both footpoints). For this JOP, the array of available images will provide simultaneous monitoring of different atmospheric layers over a wide temperature range : - MDI : photosphere, magnetic field - TRACE : transition region - EIT : corona (1 - 2. x 10^6 K) - YOHKOH : corona ( > 3. x 10^6 K) Moreover, in order to obtain additional diagnostics (single-line emission, doppler shifts, line broadenings over local features or sections of extended structures, CDS and SUMER spectra will be acquired at the highest possible rate, which excludes any rastering. MDI magnetograms will be extremely useful to follow the evolution of small magnetic elements at the footpoints of coronal magnetic structures. TARGETS Almost any target is scientifically appropriate for this joint study. We can cite active regions (loops, transient brightenings), bright points and the quiet Sun network (blinkers, network flares, manifestations of the "magnetic carpet"), coronal holes (bright points, jets, plasma waves)), both on the disc and at the limb. However, several constraints reduce the number of available targets to the point where a target of opportunity (TOO) strategy must be adopted : - brightness of the target : Faint objects may require excessively long exposure times in order to achieve a sufficient signal/noise ratio. This would in turn imply reducing the nominal cadence of 15 sec. Coronal holes seem thus to be too faint. On the other hand, bright points and active regions are prime targets. For improved contrast and reduced confusion, on-disc targets are preferable. - instrument sensitivity : The choice of selected bandpasses and wavelengths is partially dictated by the brightness of the lines and by the instrument response. For example, the He II and Fe XV bands cannot be used on EIT due to the lower mirror reflectivities in those bandpasses. By contrast, excessively high fluxes are a matter of concern regarding the degradation of some instruments (SUMER, EIT), in particular if a flare occurs during the sequence. - target position : Instrument like SUMER have now a limited steering capability and the availability of a target within the MDI high-resolution subfield might be an asset. - conditions to run : Concerns about the health of those instruments imply that this JOP can only be run once or may be twice. This emphasizes the need for simultaneous support by all coronal imaging instruments and by at least one of the spectrographs, as there will probably be no second chance. - scheduling considerations : Several spacecrafts are involved, each with an independent scientific schedule. In particular, as this high-rate sequence is considered as critical by several SOHO instrument teams (SUMER, EIT), the availability of real-time commanding is mandatory. This study should thus take place either during the long NRT commanding period or during the period of 24 h/day permanent contact. MDI can only provide high-cadence magnetograms outside the continuous "helioseismology" campaign. There might be a conflict concerning telemetry allocation between CDS and SUMER. SUMER might avoid using its high telemetry submode by using its on-board memory, in order to leave enough telemetry for CDS and EIT Given those constraints, a favorable window has been found in April-May 1998. We thus propose to schedule this TOO JOP within a one-month interval, from week 17 (April 19-25) and week 20 (May 10-16). References : Berghmans, D., Clette, F. 1998, A & A, submitted Hansteen, V.H. 1997, ESA SP-404, 45 Mc Kenzie, D.E., Mullan, D.J. 1997, Solar Phys., 176, 127 Poeds, S., Boynton, G.C. 1996, A & A, 306, 610 Walsh, R.W., Bell, G.E., Hood, A.W. 1997, 171, 81 Zirker, J.B. 1993, Solar Phys, 148.43 OPERATING DETAILS EIT : (leading instrument) ____________________________ Wavelength = either of Fe XII (195 A) and Fe IX-X (171 A) LOC coordinates = TBD (center on target, include CDS & SUMER slits) Filter = Block East or West (CCD Port A or B) Exp Time = 3.0 s CCD Clears = 0 Compression = No Subfield = 4 blocks (E-W) X 3 blocks (N-S), 5.5 x 4.2 arcmin Number of images = 212 Expected cadence = 17.5 s Expected duration = 60 min Contact person : F. Clette, J. Gurman NB : - assuming a cadence of 16 sec, the telemetry buffer will be full after 244 images, if empty at the start of the sequence. A slower cadence implies a longer time before buffer saturation. - a 4x3 subfield seems necessary to include most of an AR. - Calibration lamp images : at least one full-field full-resolution exposure, before and after the sequence (those images must not be scheduled immediately before and after the run, but within a few hours). exposure : 10 sec. YOHKOH/SXT : ____________ Sequence : high-cadence subfield Filter : Al.1 (Thin Al, 1265 A, sensitivity to "cool" plasma at 3.10^6 K) Subfield : 5.5 (E-W) X 4.2 arcmin (N-S) Pointing : TBD (overlapping EIT field of view) Cadence : order of 15 sec or less (depending on instrument capabilities and required exposure time). Duration : 60 min Contact person : D. Mc Kenzie TRACE : _______ In order to achieve a cadence of about 15 s, the exposure time must stay below 10 seconds. Sensitivity estimates indicate that this can be achieved in all EUV bandpasses and for the 1216 and 1600 Angstroms. The best sensitivities are obtained in the 171 A and 1600 A bandpasses. Those bandpasses would be considered first. However, as the 284 A sensitivity is much higher for TRACE than for EIT, this choice must also be considered. Below, we give a general definition which will be refined after TRACE is commissioned. Sequence : high-cadence subfield Wavelength : either of Fe IX-X (171 A) and Fe XII (195 A), complementary to EIT's bandpass, or Ly Alpha (1216) Resolution : 1 arcsec, no binning Subfield : 5.5 (E-W) X 4.2 arcmin (N-S) Pointing : TBD at least 24 hours in advance (overlapping EIT field of view) Cadence : TBD (cadences down to 10 sec are possible) Duration : 60 min Contact person : C. Kankelborg MDI : _____ Study : high-cadence subfield magnetogram sequence Resolution : 4 arcsec (full disk mode, to allow target selection anywhere on the disc) or high-resolution mode if the target happens to lie somewhere in the high-resolution subfield Subfield : 5.5 arcsec (E-W) X 4.2 arcmin (N-S) Pointing : TBD (overlapping EIT field of view) Cadence : 1 min Duration : 60 min Contact person : C. Deforest CDS : _____ High time cadence NIS spectra of a coronal line formed at a temperature close to the range observed by EIT (1x10^6 K). No rastering, but rotation compensation every 16 minutes. The slit will be placed over a selected structure (e.g. loop footpoint) within EIT's field of view Study : TIME17W (study ID 167, var. 1) Duration = 70 min Rotation compensation : adapted for the expected rotation rate (4 pointings during the sequence, every 15 min). Pointing : TBD (accuracy 10 arcsec) NB : Ideally, the CDS and SUMER pointing should be the same (bright features/loops). + Study : HeII2P (study 11, var. 13) (for position determination) Duration : 16 min Pointing : the same as the last pointing of the TIME17W Contact person : A. Fludra -------------------------------------------------------------------------------- CDS STUDY DEFINITION Study Title: TIME SERIES, 17 MIN, 4X240 SLIT Obs prog: TIME17W Category: Science Zone ID : 5 (ACTIVE) Study ID #167 Variation ID #1 Title ID #299 Number of rasters: 1 Raster ID Var. ID Pointing Xpos Ypos Duration Repeat 1(N) 136 1 Deferred 0 0 983 1 Duration of study as defined above: 983 seconds. (00:16:23) -------------------------------------------------------------------------------- CDS raster definition for NIS ------------------------------- FUNDAMENTAL raster ID: #136 {Slit(4x240).Posns(70,-)@(0,-) steps} Slit: #5 - (4 x 240) arcsecs Size of mirror steps: 0 arcsecs Number of mirror locations: 70 Raster VARIATION ID: #1 {(4x200) arcsec, 10s Comp. 2 IDs-(180,243)} Exposure time: 10.0 secs Compression scheme: Truncate to 12 bits VDS readout orientation: Row VDS mapping mode: Normal Telemetry required: Medium Raster duration: 983.0 seconds Raster usable?: Y -------------------------------------------------------------------------------- Line list #180 for detector NIS - 3 lines. Description: EIT Fast Wavelength Line name order Band Pixel 364.47 (Fe XII 1 1 811 367.93 (Mg IX 1 1 860 624.94 (Mg X 1 2 956 -------------------------------------------------------------------------------- SUMER : ________ AR-high-cadence-oscillation study without rotation compensation Pointing : TBD (the slit can be moved horizonally about +-100") Duration : 32 min (Observations) + 75 min (clear buffer) Contact person : K. Muglach -------------------------------------------------------------------------------- SUMER STUDY DEFINITION Parameter List for SUMER Study: AR-high-cadence-osc Item # 0 ----------------------------------------------------- You have selected (Irrelevant points are not listed.): 1. Interruption or flag mode: No interruption. 2. Slit 2 with 1*300 arcsec^2. 3. Initial pointing: (x-ii) = 0.000000 arcsec (y_ii) = 0.000000 arcsec SOHO roll angle: 0.000000 deg 3. Initial pointing: (Y) = 0.000000 arcsec (Z) = 0.000000 arcsec 4. Solar rotation: Standard compensation. S. Binning (spectral) = 1 (spatial) = 1 6. Compression: 5. Quasilog-min-max (0.92 s). Flat-field correction: ON 7. Reference pixel 1: 700 on detector B Ion(s) in band 1: N V .... 1238.82 Angstroem SI I .... 1256.49 Angstroem MG X .... 624.943 Angstroem Spectral window(s) (pixel): 25 8. Image format: Format #12 (25*360, B1); 3 time(s) 9. Spectrohelio mode: Spectrohelio 3 Scans back and forth. Integration time: 4.00000 s Step size: 0.000000 arcsec or 0 units. Image number: 1.00000 17. Your selection requires a mean telemetry rate of: 54.0000 kbit/s Available bitrate: 10.0000 kbit/s This item will run for approximately: 19.9514 minutes and will cover a solar area defined by 300 px time(s) 0.000000 arcsec Note that the memory monitoring and the run times are not very accurate. The run times just give the total exposure times with a margin of 1%, but the grating focus adjust time is included. More detailed information can be provided by the SUMER Simulator. All items up to now will run for approximately: 19.9514 minutes The memory is full after 15.1398 minutes. You have to modify your study accordingly. This study ends in a wavelength range (converted to 1st order) longer than Lyman alpha. 2,6 sec overloadtime/image 290 images (6,6 sec/im) -------------------------------------------------------------------------------- /* SUMER Simulator 3.0 created by D. Germerott MPAe Lindau/Harz */ /* Simulated with VMS IDL 4.0 on Tue May 13 15:35:08 1997 */ /* Log for: SCIENCE:[MUGLACHIAR-HIGH-CADENCE-OSC No Parameters % I % UDP/POP ended regularly - no Errors % I % Duration of Simulation: 698.665 Seconds Detector used B TM_Rate used 10500 Bit/s Intrinsic UDP duration [Sec] : 1932 (= 32 min = 0 h 32 min) Time to finally clear memory [min] : 75.46 Total duration of UDP [min] : 107.66 Total accumulated Counts for UDP : 6.781E+07 Max Total Counts/sec for UDP : 36875. Max Counts/Px/sec for UDP : 2.77 Peek Size of used Memory [KB] : 5733 (= 99 % ) Produced Image Data (inc Header)[MBI : 7.63 Total number of Images produced : 870 Effective Science Telemetry : 96 % Size of UDP is 617 Bytes, UDP needs 1 Slot(s) in SUMER DPU Number of used Parameters 0 UDP needs 0 Slot(s) for Parameter in SUMER DPU Wavelength range: 21.132 A (2nd order) 42.265 A (lst order) ttt Minimum wavelength: 612.84 A (2nd order) 1225.69 A (lst order) Item: 0 Maximum wavelength: 633.97 A (2nd order) 1267.95 A (lst order) Detector B = 43.039 mA ; Central wavelength: 1246.93 A Band 1 N V : 1238.82 A (px=700) SI 1 : 1256.49 A (px=289) MG X : 624.943 A (px=442) Slit length: 306.02792 px Slit centre: centred (#2) Window width: 25 px Wavelengths at edge of right attenuator: 633.33 A (2nd order) 1266.66 A (1st order) Wavelengths at right edge of KBr: 628.66 A (2nd order) 1257.32 A (1st order) Wavelengths at left edge of KBr: 618.16 A (2nd order) 1236.32 A (1st order) Wavelengths at edge of left attenuator: 613.60 A (2nd order) 1227.20 A (1st order) Wavelength of line 1: 1238.82 A on Ref_Pixel 700 --------------------------------------------------------------------------------