JOP 122 Micro-scale heating blocks of the solar atmosphere J.G. Doyle, L. Teriaca, M. S. Madjarska, R.Erdelyi Received: 11 April 2000; Revised 7 February 2001 Background ========== With the launch of SOHO, the idea of a quiescent solar atmosphere, especially when observed in transition region (TR) lines, has been replaced with an extremely dynamic picture in which variability is observed on all time and spatial scales. Some of the instruments on board SOHO (e.g. SUMER & CDS) have detected series of transient phenomena, such as UV explosive events and blinkers, which are still not well understood. It is assumed that they are a result of reconnection processes and a part of a more generalised class of reconnection events such as microflares and nanoflares. Then arises the question whether all these events are a signature of a possible coronal heating mechanism. Despite the large number of observational works on UV explosive events and blinkers, large uncertainties about their basic physical parameters such as electron density and temperature still exist (Teriaca et al 2001). Here we propose to study the spatial and temporal evolution of explosive events and associated structures by combining EUV observations with SUMER, CDS and TRACE. The combined data sets will be used to determine their electron density and to study their structure with changing temperature from the transition region to the corona (if indeed such a structure exists). SUMER ===== We plan to obtain new observations in the density sensitive O IV lines around 1400 Angstroms. The observations should be carried out in the frame-set of JOP 122. Our idea consists in obtaining a series of spectra with a cadence of 30 seconds using the 1 x 120 slit. After each exposure, four windows of 50 pixels each should be retained. These four windows should be taken one exactly beside one another, in such a way as to cover the spectral range from 1400 to 1408.6 angstrom (assuming a dispersion of 0.043 AA/pix). This will include the O IV 1401, Si IV 1402, O IV 1404 + O III 702.34 + S IV 1404.77, O III + S IV 1406.076 and O III 703.85 + O IV 1407. All those lines allow one to evaluate the importance of the blends in the O IV 1404 line. The four windows will be then recomposed and reduced as an unique image. We would like to observe the quiet Sun as long as possible looking for explosive events and blinkers. The temporal series should be opened and closed (and, maybe, even interspersed) with full detector spectra obtained with the same slit and grating angle but with higher exposure time (let say 120 s). The lines need to be positioned on KBr, taking care that the strong Si IV 1393 is on the bare part of the detector. An additional idea is to obtain a full spectrum around 761 Angstrom, i.e. in the O V 761 density sensitive multiplet. These observation should be obtained before or after the ones in O IV on the same pointing position. The idea is to check the consistency of the average density value found with both line ratios. The sequences should be run as follows: 1) full 1024 pixel spectrum centered at 761A .. exp= 120 sec 2) full 1024 pixel spectrum centered at 1404 .. exp= 300 sec 3) 4 windows centered at 1401.075, 1403.096, 1405.117, 1407.138A, exp=30 sec, repeat 120 times 4) full 1024 pixel spectrum centered at 1404 .. exp= 120 5) 4 windows centered at 1401.075, 1403.096, 1405.117, 1407.138A, exp=30 sec, repeat 120 times 6) full 1024 pixel spectrum centered at 1404 .. exp= 120 7) 4 windows centered at 1401.075, 1403.096, 1405.117, 1407.138A, exp=30 sec, repeat 120 times 8)full 1024 pixel spectrum centered at 1404 .. exp= 120 sec 9)4 windows centered at 1401.075, 1403.096, 1405.117, 1407.138A, exp=30 sec, repeat 120 times 10)full 1024 pixel spectrum centered at 1404 .. exp= 120 sec 11)full 1024 pixel spectrum centered at 760A .. exp= 300 sec CDS === Re-run the following sequence BUT changing the wavelength of OV in both CHROM_N7 & CHROM_N6 so that the line is positioned in the center of the window, i.e. use 629.7A. CHROM_N7 ID=35 VAR =55 5 lines Ca X 574.03, He I 584.33, O III 599.57, Mg IX 368.09, O V 628.45 slit N 4 exposure time 35 sec raster size 120'' x 240'' duration = 42 mins ============ CHROM_N6 ID=154 VAR=3 He I 584.33, O II 599.57, O V 628.45 slit N 4 exposure time 20 sec size 2'' x 240'' duration = 85 mins ============ The observations to be done in the following order: CHROM_N7 CHROM_N6 CHROM_N7 CHROM_N6 CHROM_N7 duration - 4 hours 57 minutes TRACE: ====== observe only the 171A and 195A lines FOV in pixels - 768 x 768 pixels (0.52" pixel size) exposure time - between 40 - 60 sec in each line. total 5 hrs. pointing from SUMER =====================